Publications by authors named "Paul V Dunlap"

28 Publications

  • Page 1 of 1

Shedding Light on Specificity: Population Genomic Structure of a Symbiosis Between a Coral Reef Fish and Luminous Bacterium.

Front Microbiol 2019 19;10:2670. Epub 2019 Nov 19.

Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, United States.

All organisms depend on symbiotic associations with bacteria for their success, yet how these interspecific interactions influence the population structure, ecology, and evolution of microbial symbionts is not well understood. Additionally, patterns of genetic variation in interacting species can reveal ecological traits that are important to gene flow and co-evolution. In this study, we define patterns of spatial and temporal genetic variation of a coral reef fish, , and its luminous bacterial symbiont, in the Okinawa Islands, Japan. Using restriction site-associated sequencing (RAD-Seq) methods, we show that populations of the facultative light organ symbiont of exhibit genetic structure at fine spatial scales of tens of kilometers despite the absence of physical barriers to dispersal and in contrast to populations of the host fish. These results suggest that the host's behavioral ecology and environmental interactions between host and symbiont help to structure symbiont populations in the region, consequently fostering the specificity of the association between host generations. Our approach also revealed several symbiont genes that were divergent between host populations, including and a homolog of , both of which play a role in host association in . Overall, this study highlights the important role that a host animal can play in structuring the distribution of its bacterial symbiont, particularly in highly connected marine environments, thereby promoting specificity of the symbiosis between host generations.
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http://dx.doi.org/10.3389/fmicb.2019.02670DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6879551PMC
November 2019

Draft Genome Sequences of Histamine- and Non-Histamine-Producing Photobacterium Strains.

Genome Announc 2016 Sep 22;4(5). Epub 2016 Sep 22.

FDA, Division of Seafood Science and Technology, Gulf Coast Seafood Laboratory, Dauphin Island, Alabama, USA.

Histamine-producing bacteria (HPBs) have recently been identified from the marine environment. The identification and characterization of HPBs is important to developing effective mitigation strategies for scombrotoxin fish poisoning. We report here the draft genomes of seven histamine-producing and two non-histamine-producing marine Photobacterium strains.
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http://dx.doi.org/10.1128/genomeA.01008-16DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5034137PMC
September 2016

Genome Evolution in the Obligate but Environmentally Active Luminous Symbionts of Flashlight Fish.

Genome Biol Evol 2016 08 3;8(7):2203-13. Epub 2016 Aug 3.

Department of Ecology and Evolutionary Biology, University of Michigan.

The luminous bacterial symbionts of anomalopid flashlight fish are thought to be obligately dependent on their hosts for growth and share several aspects of genome evolution with unrelated obligate symbionts, including genome reduction. However, in contrast to most obligate bacteria, anomalopid symbionts have an active environmental phase that may be important for symbiont transmission. Here we investigated patterns of evolution between anomalopid symbionts compared with patterns in free-living relatives and unrelated obligate symbionts to determine if trends common to obligate symbionts are also found in anomalopid symbionts. Two symbionts, "Candidatus Photodesmus katoptron" and "Candidatus Photodesmus blepharus," have genomes that are highly similar in gene content and order, suggesting genome stasis similar to ancient obligate symbionts present in insect lineages. This genome stasis exists in spite of the symbiont's inferred ability to recombine, which is frequently lacking in obligate symbionts with stable genomes. Additionally, we used genome comparisons and tests of selection to infer which genes may be particularly important for the symbiont's ecology compared with relatives. In keeping with obligate dependence, substitution patterns suggest that most symbiont genes are experiencing relaxed purifying selection compared with relatives. However, genes involved in motility and carbon storage, which are likely to be used outside the host, appear to be under increased purifying selection. Two chemoreceptor chemotaxis genes are retained by both species and show high conservation with amino acid sensing genes, suggesting that the bacteria may actively seek out hosts using chemotaxis toward amino acids, which the symbionts are not able to synthesize.
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http://dx.doi.org/10.1093/gbe/evw161DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4987116PMC
August 2016

Draft Genome Sequences of Histamine-Producing Photobacterium kishitanii and Photobacterium angustum, Isolated from Albacore (Thunnus alalunga) and Yellowfin (Thunnus albacares) Tuna.

Genome Announc 2015 Apr 30;3(2). Epub 2015 Apr 30.

FDA, Division of Seafood Science and Technology, Gulf Coast Seafood Laboratory, Dauphin Island, Alabama, USA.

Histamine-producing bacteria are responsible for scombrotoxin (histamine) fish poisoning, a leading cause of fish poisoning in the United States. We report here the draft genome sequences of four histamine-producing (HP) Photobacterium kishitanii strains and nine HP Photobacterium angustum strains isolated from tuna.
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http://dx.doi.org/10.1128/genomeA.00400-15DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4417705PMC
April 2015

Phylogenetic divergence between the obligate luminous symbionts of flashlight fishes demonstrates specificity of bacteria to host genera.

Environ Microbiol Rep 2014 Aug 16;6(4):331-8. Epub 2014 Jan 16.

Department of Ecology and Evolutionary Biology, University of Michigan, 830 North University Ave., Ann Arbor, MI, 48109-1048, USA.

The luminous bacterial symbionts of anomalopid flashlight fishes, which appear to be obligately dependent on their hosts for growth, share several evolutionary patterns with unrelated obligate bacteria. However, only one flashlight fish symbiont species has been characterized in detail, and it is therefore not known if the bacteria from other anomalopid species are highly divergent (a pattern common to obligate symbionts). Unlike most obligate symbionts, the bacteria symbiotic with anomalopids are extracellular and spend time outside their hosts in the environment, from which they are thought to colonize new host generations. Environmental acquisition might decrease the likelihood of bacterial divergence between host species. We used phylogenetic analysis to determine the relatedness of symbionts from different anomalopid host species. The symbionts of hosts in the genus Photoblepharon were resolved as a new species, for which we propose the name 'Candidatus Photodesmus blepharus'. Furthermore, different genera of anomalopids were found to harbour different species of bacteria, even when the hosts overlapped in geographic range. This finding suggests that the divergence between bacterial species is not the result of geographic isolation. The specificity of symbionts to host genera is consistent with obligate dependence on the host and has implications for symbiont transmission.
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http://dx.doi.org/10.1111/1758-2229.12135DOI Listing
August 2014

Genomic signatures of obligate host dependence in the luminous bacterial symbiont of a vertebrate.

Environ Microbiol 2014 Aug 8;16(8):2611-22. Epub 2013 Nov 8.

Department of Ecology and Evolutionary Biology, University of Michigan, 830 North University Ave., Ann Arbor, MI, 48109-1048, USA.

The majority of bacteria engaged in bioluminescent symbiosis are environmentally acquired and facultatively symbiotic. A few enigmatic bioluminescent symbionts have not been successfully cultured, which has led to speculation that they may be obligately dependent on their hosts. Here, we report the draft genome of the uncultured luminous symbiont of an anomalopid flashlight fish, 'Candidatus Photodesmus katoptron'. The genome of the anomalopid symbiont is reduced by 80% compared with close relatives and lacks almost all genes necessary for amino acid synthesis and for metabolism of energy sources other than glucose, supporting obligate dependence on the host for growth. 'Candidatus Photodesmus katoptron' is the first described obligate mutualistic symbiont of a vertebrate. Unlike most other obligate mutualists, the anomalopid symbiont genome has retained complete pathways for chemotaxis and motility as well as most genes involved in cell wall production, consistent with the hypothesis that these bacteria may be transmitted environmentally during an extra-host phase.
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http://dx.doi.org/10.1111/1462-2920.12302DOI Listing
August 2014

Natural replacement of vertically inherited lux-rib genes of Photobacterium aquimaris by horizontally acquired homologues.

Environ Microbiol Rep 2012 Aug 18;4(4):412-6. Epub 2012 May 18.

Interdisciplinary Research Organization Faculty of Medicine, University of Miyazaki, 5200 Kihara, Kiyotake, Miyazaki 889-1692, Japan Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA.

We report here the first instance of a complete replacement of vertically inherited luminescence genes by horizontally acquired homologues. Different strains of Photobacterium aquimaris contain homologues of the lux-rib genes that have a different evolutionary history. Strain BS1 from the Black Sea contains a vertically inherited lux-rib operon, which presumably arose in the ancestor of this species, whereas the type strain NBRC 104633(T) , from Sagami Bay, lacks the vertically inherited lux-rib operon and instead carries a complete and functional lux-rib operon acquired horizontally from a bacterium related to Photobacterium mandapamensis. The results indicate that the horizontal acquisition of the lux genes expanded the pan-genome of P. aquimaris, but it did not influence the phylogenetic divergence of this species.
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http://dx.doi.org/10.1111/j.1758-2229.2012.00355.xDOI Listing
August 2012

Historical microbiology: revival and phylogenetic analysis of the luminous bacterial cultures of M. W. Beijerinck.

FEMS Microbiol Ecol 2011 Dec 6;78(3):463-72. Epub 2011 Sep 6.

The Netherlands Culture Collection of Bacteria, CBS-KNAW Fungal Biodiversity Centre, Utrecht, The Netherlands.

Luminous bacteria isolated by Martinus W. Beijerinck were sealed in glass ampoules in 1924 and 1925 and stored under the names Photobacterium phosphoreum and 'Photobacterium splendidum'. To determine if the stored cultures were viable and to assess their evolutionary relationship with currently recognized bacteria, portions of the ampoule contents were inoculated into culture medium. Growth and luminescence were evident after 13 days of incubation, indicating the presence of viable cells after more than 80 years of storage. The Beijerinck strains are apparently the oldest bacterial cultures to be revived from storage. Multi-locus sequence analysis, based on the 16S rRNA, gapA, gyrB, pyrH, recA, luxA, and luxB genes, revealed that the Beijerinck strains are distant from the type strains of P. phosphoreum, ATCC 11040(T), and Vibrio splendidus, ATCC 33125(T), and instead form an evolutionarily distinct clade of Vibrio. Newly isolated strains from coastal seawater in Norway, France, Uruguay, Mexico, and Japan grouped with the Beijerinck strains, indicating a global distribution for this new clade, designated as the beijerinckii clade. Strains of the beijerinckii clade exhibited little sequence variation for the seven genes and approximately 6300 nucleotides examined despite the geographic distances and the more than 80 years separating their isolation. Gram-negative bacteria therefore can survive for many decades in liquid storage, and in nature, they do not necessarily diverge rapidly over time.
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http://dx.doi.org/10.1111/j.1574-6941.2011.01177.xDOI Listing
December 2011

The uncultured luminous symbiont of Anomalops katoptron (Beryciformes: Anomalopidae) represents a new bacterial genus.

Mol Phylogenet Evol 2011 Dec 16;61(3):834-43. Epub 2011 Aug 16.

Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109-1048, United States.

Flashlight fishes (Beryciformes: Anomalopidae) harbor luminous symbiotic bacteria in subocular light organs and use the bacterial light for predator avoidance, feeding, and communication. Despite many attempts anomalopid symbionts have not been brought into laboratory culture, which has restricted progress in understanding their phylogenetic relationships with other luminous bacteria, identification of the genes of their luminescence system, as well as the nature of their symbiotic interactions with their fish hosts. To begin addressing these issues, we used culture-independent analysis of the bacteria symbiotic with the anomalopid fish, Anomalops katoptron, to characterize the phylogeny of the bacteria and to identify the genes of their luminescence system including those involved in the regulation of luminescence. Analysis of the 16S rRNA, atpA, gapA, gyrB, pyrH, recA, rpoA, and topA genes resolved the A. katoptron symbionts as a clade nested within and deeply divergent from other members of Vibrionaceae. The bacterial luminescence (lux) genes were identified as a contiguous set (luxCDABEG), as found for the lux operons of other luminous bacteria. Phylogenetic analysis based on the lux genes confirmed the housekeeping gene phylogenetic placement. Furthermore, genes flanking the lux operon in the A. katoptron symbionts differed from those flanking lux operons of other genera of luminous bacteria. We therefore propose the candidate name Candidatus Photodesmus (Greek: photo = light, desmus = servant) katoptron for the species of bacteria symbiotic with A. katoptron. Results of a preliminary genomic analysis for genes regulating luminescence in other bacteria identified only a Vibrio harveyi-type luxR gene. These results suggest that expression of the luminescence system might be continuous in P. katoptron.
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http://dx.doi.org/10.1016/j.ympev.2011.08.006DOI Listing
December 2011

Functional morphology of the luminescence system of Siphamia versicolor (Perciformes: Apogonidae), a bacterially luminous coral reef fish.

J Morphol 2011 Aug 3;272(8):897-909. Epub 2011 May 3.

Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan 48109-1048, USA.

Previous studies of the luminescence system of Siphamia versicolor (Perciformes: Apogonidae) identified a ventral light organ, reflector, lens, duct, and a ventral diffuser extending from the throat to the caudal peduncle. The control and function of luminescence in this and other species of Siphamia, however, have not been defined. Morphological examination of fresh and preserved specimens identified additional components of the luminescence system involved in control and ventral emission of luminescence, including a retractable shutter over the ventral face of the light organ, contiguity of the ventral diffuser from the caudal peduncle to near the chin, and transparency of the bones and other tissues of the lower jaw. The shutter halves retract laterally, allowing the ventral release of light, and relax medially, blocking ventral light emission; topical application of norepinephrine to the exposed light organ resulted in retraction of the shutter halves, which suggests that operation of the shutter is under neuromuscular control. The extension of the diffuser to near the chin and transparency of the lower jaw allow a uniform emission of luminescence over the entire ventrum of the fish. The live aquarium-held fish were found to readily and consistently display ventral luminescence. At twilight, the fish left the protective association with their longspine sea urchin, Diadema setosum, and began to emit ventral luminescence and to feed on zooplankton. Ventral luminescence illuminated a zone below and around the fish, which typically swam close to the substrate. Shortly after complete darkness, the fish stopped feeding and emitting luminescence. These observations suggest that S. versicolor uses ventral luminescence to attract and feed on zooplankton from the reef benthos at twilight. Ventral luminescence may allow S. versicolor to exploit for feeding the gap at twilight in the presence of potential predators as the reef transitions from diurnally active to nocturnally active organisms.
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http://dx.doi.org/10.1002/jmor.10956DOI Listing
August 2011

Genome sequence of Photobacterium mandapamensis strain svers.1.1, the bioluminescent symbiont of the cardinal fish Siphamia versicolor.

J Bacteriol 2011 Jun 8;193(12):3144-5. Epub 2011 Apr 8.

Interdisciplinary Research Organization, University of Miyazaki, Kiyotake, Miyazaki 889-1692, Japan.

Photobacterium mandapamensis is one of three luminous Photobacterium species able to form species-specific bioluminescent symbioses with marine fishes. Here, we present the draft genome sequence of P. mandapamensis strain svers.1.1, the bioluminescent symbiont of the cardinal fish Siphamia versicolor, the first genome of a symbiotic, luminous Photobacterium species to be sequenced. Analysis of the sequence provides insight into differences between P. mandapamensis and other luminous and symbiotic bacteria in genes involved in quorum-sensing regulation of light production and establishment of symbiosis.
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http://dx.doi.org/10.1128/JB.00370-11DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3133217PMC
June 2011

Beijerinck and the bioluminescent bacteria: microbiological experiments in the late 19th and early 20th centuries.

FEMS Microbiol Ecol 2011 Feb 6;75(2):185-94. Epub 2010 Dec 6.

Department of Biotechnology, Delft University of Technology, Delft, The Netherlands.

Microbiological research in the days before specialized equipment, or even electricity, required a great deal of ingenuity. The revival of 90-year-old bioluminescent bacteria from Beijerinck's laboratory in Delft prompted a review of his work with these microorganisms and revealed their use in simple techniques for the investigation of, among other things, sugar metabolism in yeasts, oxygen generation and uptake and even the survival of microorganisms in liquid hydrogen. He used variant strains of bioluminescent bacteria in an attempt to study heredity and variation in biological systems and described one of the earliest examples of enzyme induction.
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http://dx.doi.org/10.1111/j.1574-6941.2010.01004.xDOI Listing
February 2011

Phylogeny, genomics, and symbiosis of Photobacterium.

FEMS Microbiol Rev 2011 Mar 30;35(2):324-42. Epub 2010 Sep 30.

Interdisciplinary Research Organization, University of Miyazaki, Miyazaki, Japan.

Photobacterium comprises several species in Vibrionaceae, a large family of Gram-negative, facultatively aerobic, bacteria that commonly associate with marine animals. Members of the genus are widely distributed in the marine environment and occur in seawater, surfaces, and intestines of marine animals, marine sediments and saline lake water, and light organs of fish. Seven Photobacterium species are luminous via the activity of the lux genes, luxCDABEG. Much recent progress has been made on the phylogeny, genomics, and symbiosis of Photobacterium. Phylogenetic analysis demonstrates a robust separation between Photobacterium and its close relatives, Aliivibrio and Vibrio, and reveals the presence of two well-supported clades. Clade 1 contains luminous and symbiotic species and one species with no luminous members, and Clade 2 contains mostly nonluminous species. The genomes of Photobacterium are similar in size, structure, and organization to other members of Vibrionaceae, with two chromosomes of unequal size and multiple rrn operons. Many species of marine fish form bioluminescent symbioses with three Photobacterium species: Photobacterium kishitanii, Photobacterium leiognathi, and Photobacterium mandapamensis. These associations are highly, but not strictly species specific, and they do not exhibit symbiont-host codivergence. Environmental congruence instead of host selection might explain the patterns of symbiont-host affiliation observed from nature.
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http://dx.doi.org/10.1111/j.1574-6976.2010.00250.xDOI Listing
March 2011

Multi-gene analysis reveals previously unrecognized phylogenetic diversity in Aliivibrio.

Syst Appl Microbiol 2009 Sep 29;32(6):379-86. Epub 2009 May 29.

Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109-1048, USA.

The "Vibrio fischeri species group" recently was reclassified as a new genus, Aliivibrio, comprising four species, Aliivibrio fischeri, Aliivibrio logei, Aliivibrio salmonicida, and Aliivibrio wodanis. Only limited phylogenetic analysis of strains within Aliivibrio has been carried out, however, and taxonomic ambiguity is evident within this group, especially for phenotypically unusual strains and certain strains isolated from bioluminescent symbioses. Therefore, to examine in depth the evolutionary relationships within Aliivibrio and redefine the host affiliations of symbiotic species, we examined several previously identified and newly isolated strains using phylogenetic analysis based on multiple independent loci, gapA, gyrB, pyrH, recA, rpoA, the luxABE region, and the 16S rRNA gene. The analysis resolved Aliivibrio as distinct from Vibrio, Photobacterium, and other genera of Vibrionaceae, and resolved A. fischeri, A. salmonicida, A. logei, and A. wodanis as distinct, well-supported clades. However, it also revealed that several previously reported strains are incorrectly identified and that substantial unrecognized diversity exists in this genus. Specifically, strain ATCC 33715 (Y-1) and several other strains having a yellow-shifted luminescence were not members of A. fischeri. Furthermore, no strain previously identified as A. logei grouped with the type strain (ATCC 29985(T)), and no bona-fide strain of A. logei was identified as a bioluminescent symbiont. Several additional strains identified previously as A. logei group instead with the type strain of A. wodanis (ATCC BAA-104(T)), or are members of a new clade. Two strongly supported clades were evident within A. fischeri, a phylogenetic structure that might reflect differences in the host species or differences in the ecological incidence of strains. The results of this study highlight the importance of basing taxonomic conclusions on examination of type strains.
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http://dx.doi.org/10.1016/j.syapm.2009.04.005DOI Listing
September 2009

OscR, a new osmolarity-responsive regulator in Vibrio cholerae.

Authors:
Paul V Dunlap

J Bacteriol 2009 Jul 24;191(13):4053-5. Epub 2009 Apr 24.

Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109-1048, USA.

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http://dx.doi.org/10.1128/JB.00501-09DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2698486PMC
July 2009

Developmental and microbiological analysis of the inception of bioluminescent symbiosis in the marine fish Nuchequula nuchalis (Perciformes: Leiognathidae).

Appl Environ Microbiol 2008 Dec 31;74(24):7471-81. Epub 2008 Oct 31.

University of Michigan, Department of Ecology and Evolutionary Biology, 830 North University Avenue, Ann Arbor, MI 48109-1048, USA.

Many marine fish harbor luminous bacteria as bioluminescent symbionts. Despite the diversity, abundance, and ecological importance of these fish and their apparent dependence on luminous bacteria for survival and reproduction, little is known about developmental and microbiological events surrounding the inception of their symbioses. To gain insight on these issues, we examined wild-caught larvae of the leiognathid fish Nuchequula nuchalis, a species that harbors Photobacterium leiognathi as its symbiont, for the presence, developmental state, and microbiological status of the fish's internal, supraesophageal light organ. Nascent light organs were evident in the smallest specimens obtained, flexion larvae of 6.0 to 6.5 mm in notochord length (NL), a developmental stage at which the stomach had not yet differentiated and the nascent gasbladder had not established an interface with the light organ. Light organs of certain of the specimens in this size range apparently lacked bacteria, whereas light organs of other specimens of 6.5 mm in NL and of all larger specimens harbored large populations of bacteria, representatives of which were identified as P. leiognathi. Bacteria identified as Vibrio harveyi were also present in the light organ of one larval specimen. Light organ populations were composed typically of two or three genetically distinct strain types of P. leiognathi, similar to the situation in adult fish, and the same strain type was only rarely found in light organs of different larval, juvenile, or adult specimens. Light organs of larvae carried a smaller proportion of strains merodiploid for the lux-rib operon, 79 of 249 strains, than those of adults (75 of 91 strains). These results indicate that light organs of N. nuchalis flexion and postflexion larvae of 6.0 to 6.7 mm in NL are at an early stage of development and that inception of the symbiosis apparently occurs in flexion larvae of 6.0 to 6.5 mm in NL. Ontogeny of the light organ therefore apparently precedes acquisition of the symbiotic bacteria. Furthermore, bacterial populations in larval light organs near inception of the symbiosis are genetically diverse, like those of adult fish.
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http://dx.doi.org/10.1128/AEM.01619-08DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2607158PMC
December 2008

Phylogenetic analysis of the incidence of lux gene horizontal transfer in Vibrionaceae.

J Bacteriol 2008 May 21;190(10):3494-504. Epub 2008 Mar 21.

Department of Ecology and Evolutionary Biology, 830 North University Avenue, University of Michigan, Ann Arbor, MI 48109-1048, USA.

Horizontal gene transfer (HGT) is thought to occur frequently in bacteria in nature and to play an important role in bacterial evolution, contributing to the formation of new species. To gain insight into the frequency of HGT in Vibrionaceae and its possible impact on speciation, we assessed the incidence of interspecies transfer of the lux genes (luxCDABEG), which encode proteins involved in luminescence, a distinctive phenotype. Three hundred three luminous strains, most of which were recently isolated from nature and which represent 11 Aliivibrio, Photobacterium, and Vibrio species, were screened for incongruence of phylogenies based on a representative housekeeping gene (gyrB or pyrH) and a representative lux gene (luxA). Strains exhibiting incongruence were then subjected to detailed phylogenetic analysis of horizontal transfer by using multiple housekeeping genes (gyrB, recA, and pyrH) and multiple lux genes (luxCDABEG). In nearly all cases, housekeeping gene and lux gene phylogenies were congruent, and there was no instance in which the lux genes of one luminous species had replaced the lux genes of another luminous species. Therefore, the lux genes are predominantly vertically inherited in Vibrionaceae. The few exceptions to this pattern of congruence were as follows: (i) the lux genes of the only known luminous strain of Vibrio vulnificus, VVL1 (ATCC 43382), were evolutionarily closely related to the lux genes of Vibrio harveyi; (ii) the lux genes of two luminous strains of Vibrio chagasii, 21N-12 and SB-52, were closely related to those of V. harveyi and Vibrio splendidus, respectively; (iii) the lux genes of a luminous strain of Photobacterium damselae, BT-6, were closely related to the lux genes of the lux-rib(2) operon of Photobacterium leiognathi; and (iv) a strain of the luminous bacterium Photobacterium mandapamensis was found to be merodiploid for the lux genes, and the second set of lux genes was closely related to the lux genes of the lux-rib(2) operon of P. leiognathi. In none of these cases of apparent HGT, however, did acquisition of the lux genes correlate with phylogenetic divergence of the recipient strain from other members of its species. The results indicate that horizontal transfer of the lux genes in nature is rare and that horizontal acquisition of the lux genes apparently has not contributed to speciation in recipient taxa.
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http://dx.doi.org/10.1128/JB.00101-08DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2394989PMC
May 2008

Reclassification of Vibrio fischeri, Vibrio logei, Vibrio salmonicida and Vibrio wodanis as Aliivibrio fischeri gen. nov., comb. nov., Aliivibrio logei comb. nov., Aliivibrio salmonicida comb. nov. and Aliivibrio wodanis comb. nov.

Int J Syst Evol Microbiol 2007 Dec;57(Pt 12):2823-2829

Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109-1048, USA.

Four closely related species, Vibrio fischeri, Vibrio logei, Vibrio salmonicida and Vibrio wodanis, form a clade within the family Vibrionaceae; the taxonomic status and phylogenetic position of this clade have remained ambiguous for many years. To resolve this ambiguity, we tested these species against other species of the Vibrionaceae for phylogenetic and phenotypic differences. Sequence identities for the 16S rRNA gene were > or =97.4 % among members of the V. fischeri group, but were < or =95.5 % for members of this group in comparison with type species of other genera of the Vibrionaceae (i.e. Photobacterium and Vibrio, with which they overlap in G+C content, and Enterovibrio, Grimontia and Salinivibrio, with which they do not overlap in G+C content). Combined analysis of the recA, rpoA, pyrH, gyrB and 16S rRNA gene sequences revealed that the species of the V. fischeri group form a tightly clustered clade, distinct from these other genera. Furthermore, phenotypic traits differentiated the V. fischeri group from other genera of the Vibrionaceae, and a panel of 13 biochemical tests discriminated members of the V. fischeri group from type strains of Photobacterium and Vibrio. These results indicate that the four species of the V. fischeri group represent a lineage within the Vibrionaceae that is distinct from other genera. We therefore propose their reclassification in a new genus, Aliivibrio gen. nov. Aliivibrio is composed of four species: Aliivibrio fischeri comb. nov. (the type species) (type strain ATCC 7744(T) =CAIM 329(T) =CCUG 13450(T) =CIP 103206(T) =DSM 507(T) =LMG 4414(T) =NCIMB 1281(T)), Aliivibrio logei comb. nov. (type strain ATCC 29985(T) =CCUG 20283(T) =CIP 104991(T) =NCIMB 2252(T)), Aliivibrio salmonicida comb. nov. (type strain ATCC 43839(T) =CIP 103166(T) =LMG 14010(T) =NCIMB 2262(T)) and Aliivibrio wodanis comb. nov. (type strain ATCC BAA-104(T) =NCIMB 13582(T) =LMG 24053(T)).
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http://dx.doi.org/10.1099/ijs.0.65081-0DOI Listing
December 2007

Photobacterium kishitanii sp. nov., a luminous marine bacterium symbiotic with deep-sea fishes.

Int J Syst Evol Microbiol 2007 Sep;57(Pt 9):2073-2078

Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA.

Six representatives of a luminous bacterium commonly found in association with deep, cold-dwelling marine fishes were isolated from the light organs and skin of different fish species. These bacteria were Gram-negative, catalase-positive, and weakly oxidase-positive or oxidase-negative. Morphologically, cells of these strains were coccoid or coccoid-rods, occurring singly or in pairs, and motile by means of polar flagellation. After growth on seawater-based agar medium at 22 degrees C for 18 h, colonies were small, round and white, with an intense cerulean blue luminescence. Analysis of 16S rRNA gene sequence similarity placed these bacteria in the genus Photobacterium. Phylogenetic analysis based on seven housekeeping gene sequences (16S rRNA gene, gapA, gyrB, pyrH, recA, rpoA and rpoD), seven gene sequences of the lux operon (luxC, luxD, luxA, luxB, luxF, luxE and luxG) and four gene sequences of the rib operon (ribE, ribB, ribH and ribA), resolved the six strains as members of the genus Photobacterium and as a clade distinct from other species of Photobacterium. These strains were most closely related to Photobacterium phosphoreum and Photobacterium iliopiscarium. DNA-DNA hybridization values between the designated type strain, Photobacterium kishitanii pjapo.1.1(T), and P. phosphoreum LMG 4233(T), P. iliopiscarium LMG 19543(T) and Photobacterium indicum LMG 22857(T) were 51, 43 and 19 %, respectively. In AFLP analysis, the six strains clustered together, forming a group distinct from other analysed species. The fatty acid C(17 : 0) cyclo was present in these bacteria, but not in P. phosphoreum, P. iliopiscarium or P. indicum. A combination of biochemical tests (arginine dihydrolase and lysine decarboxylase) differentiates these strains from P. phosphoreum and P. indicum. The DNA G+C content of P. kishitanii pjapo.1.1(T) is 40.2 %, and the genome size is approximately 4.2 Mbp, in the form of two circular chromosomes. These strains represent a novel species, for which the name Photobacterium kishitanii sp. nov. is proposed. The type strain, pjapo.1.1(T) (=ATCC BAA-1194(T)=LMG 23890(T)), is a luminous symbiont isolated from the light organ of the deep-water fish Physiculus japonicus.
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http://dx.doi.org/10.1099/ijs.0.65153-0DOI Listing
September 2007

Natural merodiploidy of the lux-rib operon of Photobacterium leiognathi from coastal waters of Honshu, Japan.

J Bacteriol 2007 Sep 22;189(17):6148-58. Epub 2007 Jun 22.

Department of Ecological and Evolutionary Biology, University of Michigan, 830 North University Ave., Ann Arbor, MI 48109-1048, USA.

Sequence analysis of the bacterial luminescence (lux) genes has proven effective in helping resolve evolutionary relationships among luminous bacteria. Phylogenetic analysis using lux genes, however, is based on the assumptions that the lux genes are present as single copies on the bacterial chromosome and are vertically inherited. We report here that certain strains of Photobacterium leiognathi carry multiple phylogenetically distinct copies of the entire operon that codes for luminescence and riboflavin synthesis genes, luxCDABEG-ribEBHA. Merodiploid lux-rib strains of P. leiognathi were detected during sequence analysis of luxA. To define the gene content, organization, and sequence of each lux-rib operon, we constructed a fosmid library of genomic DNA from a representative merodiploid strain, lnuch.13.1. Sequence analysis of fosmid clones and genomic analysis of lnuch.13.1 defined two complete, physically separate, and apparently functional operons, designated lux-rib1 and lux-rib2. P. leiognathi strains lelon.2.1 and lnuch.21.1 were also found to carry lux-rib1 and lux-rib2, whereas ATCC 25521T apparently carries only lux-rib1. In lnuch.13.1, lelon.2.1, lnuch.21.1, and ATCC 25521T, lux-rib1 is flanked upstream by lumQ and putA and downstream by a gene for a hypothetical multidrug efflux pump. In contrast, transposase genes flank lux-rib2 of lnuch.13.1, and the chromosomal location of lux-rib2 apparently differs in lnuch.13.1, lelon.2.1, and lnuch.21.1. Phylogenetic analysis demonstrated that lux-rib1 and lux-rib2 are more closely related to each other than either one is to the lux and rib genes of other bacterial species, which rules out interspecies lateral gene transfer as the origin of lux-rib2 in P. leiognathi; lux-rib2 apparently arose within a previously unsampled or extinct P. leiognathi lineage. Analysis of 170 additional strains of P. leiognathi, for a total of 174 strains examined from coastal waters of Japan, Taiwan, the Philippine Islands, and Thailand, identified 106 strains that carry only a single lux-rib operon and 68 that carry multiple lux-rib operons. Strains bearing a single lux-rib operon were obtained throughout the geographic sampling range, whereas lux-rib merodiploid strains were found only in coastal waters of central Honshu. This is the first report of merodiploidy of lux or rib genes in a luminous bacterium and the first indication that a natural merodiploid state in bacteria can correlate with geography.
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http://dx.doi.org/10.1128/JB.00672-07DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1951928PMC
September 2007

Analysis of LuxR regulon gene expression during quorum sensing in Vibrio fischeri.

J Bacteriol 2007 Jun 30;189(11):4127-34. Epub 2007 Mar 30.

Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, USA.

The regulation of the lux operon (luxICDABEG) of Vibrio fischeri has been intensively studied as a model for quorum sensing in proteobacteria. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis previously identified several non-Lux proteins in V. fischeri MJ-100 whose expression was dependent on LuxR and 3-oxo-hexanoyl-l-homoserine lactone (3-oxo-C6-HSL). To determine if the LuxR-dependent regulation of the genes encoding these proteins was due to direct transcriptional control by LuxR and 3-oxo-C6-HSL or instead was due to indirect control via an unidentified regulatory element, promoters of interest were cloned into a lacZ reporter and tested for their LuxR and 3-oxo-C6-HSL dependence in recombinant Escherichia coli. The promoters for qsrP, acfA, and ribB were found to be directly activated via LuxR-3-oxo-C6-HSL. The sites of transcription initiation were established via primer extension analysis. Based on this information and the position of the lux box-binding site near position -40, all three promoters appear to have a class II-type promoter structure. In order to more fully characterize the LuxR regulon in V. fischeri MJ-100, real-time reverse transcription-PCR was used to study the temporal expression of qsrP, acfA, and ribB during the exponential and stationary phases of growth, and electrophoretic mobility shift assays were used to compare the binding affinities of LuxR to the promoters under investigation. Taken together, the results demonstrate that regulation of the production of QsrP, RibB, and AcfA is controlled directly by LuxR at the level of transcription, thereby establishing that there is a LuxR regulon in V. fischeri MJ-100 whose genes are coordinately expressed during mid-exponential growth.
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http://dx.doi.org/10.1128/JB.01779-06DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1913387PMC
June 2007

Phylogenetic diversity and cosymbiosis in the bioluminescent symbioses of "Photobacterium mandapamensis".

Appl Environ Microbiol 2007 May 16;73(10):3173-82. Epub 2007 Mar 16.

Department of Ecology and Evolutionary Biology, 830 North University Avenue, University of Michigan, Ann Arbor, MI 48109-1048, USA.

"Photobacterium mandapamensis" (proposed name) and Photobacterium leiognathi are closely related, phenotypically similar marine bacteria that form bioluminescent symbioses with marine animals. Despite their similarity, however, these bacteria can be distinguished phylogenetically by sequence divergence of their luminescence genes, luxCDAB(F)E, by the presence (P. mandapamensis) or the absence (P. leiognathi) of luxF and, as shown here, by the sequence divergence of genes involved in the synthesis of riboflavin, ribBHA. To gain insight into the possibility that P. mandapamensis and P. leiognathi are ecologically distinct, we used these phylogenetic criteria to determine the incidence of P. mandapamensis as a bioluminescent symbiont of marine animals. Five fish species, Acropoma japonicum (Perciformes, Acropomatidae), Photopectoralis panayensis and Photopectoralis bindus (Perciformes, Leiognathidae), Siphamia versicolor (Perciformes, Apogonidae), and Gadella jordani (Gadiformes, Moridae), were found to harbor P. mandapamensis in their light organs. Specimens of A. japonicus, P. panayensis, and P. bindus harbored P. mandapamensis and P. leiognathi together as cosymbionts of the same light organ. Regardless of cosymbiosis, P. mandapamensis was the predominant symbiont of A. japonicum, and it was the apparently exclusive symbiont of S. versicolor and G. jordani. In contrast, P. leiognathi was found to be the predominant symbiont of P. panayensis and P. bindus, and it appears to be the exclusive symbiont of other leiognathid fishes and a loliginid squid. A phylogenetic test for cospeciation revealed no evidence of codivergence between P. mandapamensis and its host fishes, indicating that coevolution apparently is not the basis for this bacterium's host preferences. These results, which are the first report of bacterial cosymbiosis in fish light organs and the first demonstration that P. leiognathi is not the exclusive light organ symbiont of leiognathid fishes, demonstrate that the host species ranges of P. mandapamensis and P. leiognathi are substantially distinct. The host range difference underscores possible differences in the environmental distributions and physiologies of these two bacterial species.
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http://dx.doi.org/10.1128/AEM.02212-06DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1907103PMC
May 2007

Phylogenetic resolution and habitat specificity of members of the Photobacterium phosphoreum species group.

Environ Microbiol 2005 Oct;7(10):1641-54

Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA.

Substantial ambiguity exists regarding the phylogenetic status of facultatively psychrophilic luminous bacteria identified as Photobacterium phosphoreum, a species thought to be widely distributed in the world's oceans and believed to be the specific bioluminescent light-organ symbiont of several deep-sea fishes. Members of the P. phosphoreum species group include luminous and non-luminous strains identified phenotypically from a variety of different habitats as well as phylogenetically defined lineages that appear to be evolutionarily distinct. To resolve this ambiguity and to begin developing a meaningful knowledge of the geographic distributions, habitats and symbiotic relationships of bacteria in the P. phosphoreum species group, we carried out a multilocus, fine-scale phylogenetic analysis based on sequences of the 16S rRNA, gyrB and luxABFE genes of many newly isolated luminous strains from symbiotic and saprophytic habitats, together with previously isolated luminous and non-luminous strains identified as P. phosphoreum from these and other habitats. Parsimony analysis unambiguously resolved three evolutionarily distinct clades, phosphoreum, iliopiscarium and kishitanii. The tight phylogenetic clustering within these clades and the distinct separation between them indicates they are different species, P. phosphoreum, Photobacterium iliopiscarium and the newly recognized 'Photobacterium kishitanii'. Previously reported non-luminous strains, which had been identified phenotypically as P. phosphoreum, resolved unambiguously as P. iliopiscarium, and all examined deep-sea fishes (specimens of families Chlorophthalmidae, Macrouridae, Moridae, Trachichthyidae and Acropomatidae) were found to harbour 'P. kishitanii', not P. phosphoreum, in their light organs. This resolution revealed also that 'P. kishitanii' is cosmopolitan in its geographic distribution. Furthermore, the lack of phylogenetic variation within 'P. kishitanii' indicates that this facultatively symbiotic bacterium is not cospeciating with its phylogenetically divergent host fishes. The results of this fine-scale phylogenetic analysis support the emerging view that bacterial species names should designate singular historical entities, i.e. discrete lineages diagnosed by a significant divergence of shared derived nucleotide characters.
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http://dx.doi.org/10.1111/j.1462-2920.2005.00859.xDOI Listing
October 2005

Genomic and phylogenetic characterization of luminous bacteria symbiotic with the deep-sea fish Chlorophthalmus albatrossis (Aulopiformes: Chlorophthalmidae).

Appl Environ Microbiol 2005 Feb;71(2):930-9

Department of Ecology and Evolutionary Biology, University of Michigan, 830 North University Ave., Ann Arbor, MI 48109-1048, USA.

Bacteria forming light-organ symbiosis with deep-sea chlorophthalmid fishes (Aulopiformes: Chlorophthalmidae) are considered to belong to the species Photobacterium phosphoreum. The identification of these bacteria as P. phosphoreum, however, was based exclusively on phenotypic traits, which may not discriminate between phenetically similar but evolutionarily distinct luminous bacteria. Therefore, to test the species identification of chlorophthalmid symbionts, we carried out a genomotypic (repetitive element palindromic PCR genomic profiling) and phylogenetic analysis on strains isolated from the perirectal light organ of Chlorophthalmus albatrossis. Sequence analysis of the 16S rRNA gene of 10 strains from 5 fish specimens placed these bacteria in a cluster related to but phylogenetically distinct from the type strain of P. phosphoreum, ATCC 11040(T), and the type strain of Photobacterium iliopiscarium, ATCC 51760(T). Analysis of gyrB resolved the C. albatrossis strains as a strongly supported clade distinct from P. phosphoreum and P. iliopiscarium. Genomic profiling of 109 strains from the 5 C. albatrossis specimens revealed a high level of similarity among strains but allowed identification of genomotypically different types from each fish. Representatives of each type were then analyzed phylogenetically, using sequence of the luxABFE genes. As with gyrB, analysis of luxABFE resolved the C. albatrossis strains as a robustly supported clade distinct from P. phosphoreum. Furthermore, other strains of luminous bacteria reported as P. phosphoreum, i.e., NCIMB 844, from the skin of Merluccius capensis (Merlucciidae), NZ-11D, from the light organ of Nezumia aequalis (Macrouridae), and pjapo.1.1, from the light organ of Physiculus japonicus (Moridae), grouped phylogenetically by gyrB and luxABFE with the C. albatrossis strains, not with ATCC 11040(T). These results demonstrate that luminous bacteria symbiotic with C. albatrossis, together with certain other strains of luminous bacteria, form a clade, designated the kishitanii clade, that is related to but evolutionarily distinct from P. phosphoreum. Members of the kishitanii clade may constitute the major or sole bioluminescent symbiont of several families of deep-sea luminous fishes.
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http://dx.doi.org/10.1128/AEM.71.2.930-939.2005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC546735PMC
February 2005

Phylogenetic analysis of the lux operon distinguishes two evolutionarily distinct clades of Photobacterium leiognathi.

Arch Microbiol 2004 May 19;181(5):352-61. Epub 2004 Mar 19.

Department of Ecology and Evolutionary Biology, Kraus Natural Science Building, 830 North University Avenue, University of Michigan, Ann Arbor, MI 48109-1048, USA.

The luminous marine bacterium Photobacterium mandapamensis was synonymized several years ago with Photobacterium leiognathi based on a high degree of phenotypic and genetic similarity. To test the possibility that P. leiognathi as now formulated, however, actually contains two distinct bacterial groups reflecting the earlier identification of P. mandapamensis and P. leiognathi as separate species, we compared P. leiognathi strains isolated from light-organ symbiosis with leiognathid fishes (i.e., ATCC 25521(T), ATCC 25587, lequu.1.1 and lleuc.1.1) with strains from seawater originally described as P. mandapamensis and later synonymized as P. leiognathi (i.e., ATCC 27561(T) and ATCC 33981) and certain strains initially identified as P. leiognathi (i.e., PL-721, PL-741, 554). Analysis of the 16S rRNA and gyrB genes did not resolve distinct clades, affirming a close relationship among these strains. However, strains ATCC 27561(T), ATCC 33981, PL-721, PL-741 and 554 were found to bear a luxF gene in the lux operon ( luxABFE), whereas ATCC 25521(T), ATCC 25587, lequu.1.1 and lleuc.1.1 lack this gene ( luxABE). Phylogenetic analysis of the luxAB(F)E region confirmed this distinction. Furthermore, ATCC 27561(T), ATCC 33981, PL-721, PL-741 and 554 all produced a higher level of luminescence on high-salt medium, as previously described for PL-721, whereas ATCC 25521(T), ATCC 25587, lequu.1.1 and lleuc.1.1 all produced a higher level of luminescence on low-salt medium, a characteristic of P. leiognathi from leiognathid fish light organs. These results demonstrate that P. leiognathi contains two evolutionarily and phenotypically distinct clades, P. leiognathi subsp. leiognathi (strains ATCC 25521(T), ATCC 25587, lequu.1.1 and lleuc.1.1), and P. leiognathi subsp. mandapamensis (strains ATCC 27561(T), ATCC 33981, PL-721, PL-741 and 554).
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http://dx.doi.org/10.1007/s00203-004-0663-7DOI Listing
May 2004

Genomic polymorphism in symbiotic populations of Photobacterium leiognathi.

Environ Microbiol 2004 Feb;6(2):145-58

Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA.

Photobacterium leiognathi forms a bioluminescent symbiosis with leiognathid fishes, colonizing the internal light organ of the fish and providing its host with light used in bioluminescence displays. Strains symbiotic with different species of the fish exhibit substantial phenotypic differences in symbiosis and in culture, including differences in 2-D PAGE protein patterns and profiles of indigenous plasmids. To determine if such differences might reflect a genetically based symbiont-strain/host-species specificity, we profiled the genomes of P. leiognathi strains from leiognathid fishes using PFGE. Individual strains from 10 species of leiognathid fishes exhibited substantial genomic polymorphism, with no obvious similarity among strains; these strains were nonetheless identified as P. leiognathi by 16S rDNA sequence analysis. Profiling of multiple strains from individual host specimens revealed an oligoclonal structure to the symbiont populations; typically one or two genomotypes dominated each population. However, analysis of multiple strains from multiple specimens of the same host species, to determine if the same strain types consistently colonize a host species, demonstrated substantial heterogeneity, with the same genomotype only rarely observed among the symbiont populations of different specimens of the same host species. Colonization of the leiognathid light organ to initiate the symbiosis therefore is likely to be oliogoclonal, and specificity of the P. leiognathi/leiognathid fish symbiosis apparently is maintained at the bacterial species level rather than at the level of individual, genomotypically defined strain types.
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http://dx.doi.org/10.1046/j.1462-2920.2003.00548.xDOI Listing
February 2004

LuxO controls luxR expression in Vibrio harveyi: evidence for a common regulatory mechanism in Vibrio.

Mol Microbiol 2003 Apr;48(2):537-48

Department of Biochemistry, Room 813, McIntyre Medical Sciences Building, McGill University, 3655 Promenade Sir William Osler, Montreal, Quebec, Canada, H3G 1Y6.

Quorum-sensing control of luminescence in Vibrio harveyi, which involves an indirect autoinducer-mediated phosphorelay signal transduction system, contrasts with the prototypical quorum-sensing system of Vibrio fischeri, in which the autoinducer and the transcriptional activator LuxR directly activate lux operon expression. In V. harveyi, a regulator not homologous to V. fischeri LuxR and also designated LuxR (LuxRvh), binds specifically to the lux operon promoter region and activates the expression of luminescence. A direct connection has not been identified previously between V. harveyi LuxRvh and the autoinducer-mediated phosphorelay system. Here, we demonstrate by mobility shift assays and measurement of luxRvh mRNA levels with luxO+ and luxO- cells that the central response regulator of the V. harveyi phosphorelay system (LuxO) represses the level of LuxRvh. Expression of a luxRvh-bearing plasmid strongly stimulated luminescence of a luxO- mutant but had no effect on luminescence of wild-type luxO+ cells, indicating tight regulation of luxRvh by LuxO. Furthermore, luxO null mutants of V. fischeri MJ-1 and two autoinducer mutants, MJ-211 (luxI-) and MJ-215 (luxI-ainS-), emitted more light and exhibited more elevated levels of litR, a newly identified V. harveyi luxRvh homologue, than their luxO+ counterparts. These results suggest that activity of the autoinducer-mediated phosphorelay system is coupled to LuxRvh/LitR control of luminescence through LuxO in V. harveyi and V. fischeri. The presence of homologues of V. harveyi LuxRvh, LuxO and other phosphorelay system proteins in various Vibrio species and the control of LuxRvh and its homologues by LuxO identified here in V. harveyi and V. fischeri and recently in Vibrio cholerae suggest that the luxO-luxRvh couple is a central feature of this quorum-sensing system in members of the genus Vibrio.
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http://dx.doi.org/10.1046/j.1365-2958.2003.03453.xDOI Listing
April 2003

PHYSIOLOGICAL AND MORPHOLOGICAL STATE OF THE SYMBIOTIC BACTERIA FROM LIGHT ORGANS OF PONYFISH.

Authors:
Paul V Dunlap

Biol Bull 1984 Oct;167(2):410-425

Symbiotic, bioluminescent bacteria (Photobacterium leiognathi) within and directly removed from the light organs of freshly sacrificed Philippine and Japanese ponyfish (family Leiognathidae) were analyzed for light production, oxygen uptake, morphology, and density. Luminescence averaged 2.4 x 10 quanta·s · cell for bacteria from 24 fish (6 species in 3 genera), more than 10 times the maximum luminescences of P. leiognathi grown in culture. Light production (depending on the in vivo quantum yield for luminescence, 0.1 to 1.0) accounted for 1.7 to 17% of the total oxygen utilized by bacteria from the light organ, substantially more than found for P. leiognathi in culture. Bacteria from the light organ were non-motile, non-flagellated coccobacilloid to short rod-shaped cells (1.6 x 3.2 µm), whereas in culture they showed motility and polar flagellation. In situ doubling time for the population of light organ bacteria was estimated to be approximately one day, or 20 to 30 times slower than in culture. Within the tubules of the light organ, the bacteria were solidly packed inside elongate, thinly-walled saccules, with one to 20 saccules tightly filling each light organ tubule. The saccules held the bacteria at a density (calculated from bacterial cell and saccule volumes) of approximately 1 x 10 cells·ml, which is a density roughly 15 times greater than estimated from total light organ volume. These findings lead to a maximalluminescence, minimal-growth bacterial model of this symbiosis.
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http://dx.doi.org/10.2307/1541286DOI Listing
October 1984