Publications by authors named "Xavier Mari"

9 Publications

  • Page 1 of 1

Amino acids promote black carbon aggregation and microbial colonization in coastal waters off Vietnam.

Sci Total Environ 2019 Oct 13;685:527-532. Epub 2019 May 13.

Aix Marseille Univ, Université de Toulon, CNRS, IRD, MIO UM 110, 13288 Marseille, France; Institute of Marine Environment and Resources (IMER), Vietnam Academy of Science and Technology (VAST), 246 Da Nang Street, Haiphong, Viet Nam; University of Science and Technology of Hanoi (USTH), Vietnam Academy of Science and Technology (VAST), Hanoi, Viet Nam.

The combustion of fossil fuels and biomass produces pyrogenic organic matter usually known as 'black carbon' (BC), which are transported across the atmosphere as particulate aerosol, eventually deposited on land and oceans. Soil studies have investigated the potential microbial colonization and remineralization of BC particles, but this process has been seldom studied in marine waters. BC provides a significant input of organic carbon to the oceans, yet its fate and role in biogeochemical cycling remains unknown. Here we explored the microbial colonization of BC particles in coastal seawater samples collected in Halong Bay (northern Vietnam). Using high-resolution mass spectrometry and microscopy methods, we observed an increasing colonization of BC particles by marine microbes in the presence of amino acids. Our results suggest that natural organic matter (NOM) present in seawater may promote the microbial colonization and eventual remineralization of BC particles. Future experiments should explore the potential microbial remineralization of BC particles to unveil the role of this massive source of carbon to marine ecosystems.
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http://dx.doi.org/10.1016/j.scitotenv.2019.05.141DOI Listing
October 2019

Origins and discrimination between local and regional atmospheric pollution in Haiphong (Vietnam), based on metal(loid) concentrations and lead isotopic ratios in PM.

Environ Sci Pollut Res Int 2018 Sep 12;25(26):26653-26668. Epub 2018 Jul 12.

CNRS, IRD, MIO UM110, Aix Marseille Université, Université de Toulon, 13288, Marseille, France.

Southeast Asia is a hotspot of anthropogenic emissions where episodes of recurrent and prolonged atmospheric pollution can lead to the formation of large haze events, giving rise to wide plumes which spread over adjacent oceans and neighbouring countries. Trace metal concentrations and Pb isotopic ratios in atmospheric particulate matter < 10 μm (PM) were used to track the origins and the transport pathways of atmospheric pollutants. This approach was used for fortnightly PM collections over a complete annual cycle in Haiphong, northern Vietnam. Distinct seasonal patterns were observed for the trace metal concentration in PM, with a maximum during the Northeast (NE) monsoon and a minimum during the Southeast (SE) monsoon. Some elements (As, Cd, Mn) were found in excess according to the World Health Organization guidelines. Coal combustion was highlighted with enrichment factors of As, Cd, Se, and Sb, but these inputs were outdistanced by other anthropogenic activities. V/Ni and Cu/Sb ratios were found to be markers of oil combustion, while Pb/Cd and Zn/Pb ratios were found to be markers of industrial activities. Pb isotopic composition in PM revealed an important contribution of soil dusts (45-60%). In PM, the Pb fraction due to oil combustion was correlated with dominant airflow pathways (31% during the north-easterlies and 20% during the south-easterlies), and the Pb fraction resulting from industrial emissions was stable (around 28%) throughout the year. During the SE monsoon, Pb inputs were mainly attributed to resuspension of local soil dusts (about 90%), and during the NE monsoon, the increase of Pb inPM was due to the mixing of local and regional inputs.
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http://dx.doi.org/10.1007/s11356-018-2722-7DOI Listing
September 2018

Colonization and release processes of viruses and prokaryotes on artificial marine macroaggregates.

FEMS Microbiol Lett 2016 Jan 13;363(1):fnv216. Epub 2015 Nov 13.

CNRS, UMR 7093, LOV, Observatoire Océanologique, 06230 Villefranche-sur-Mer, France Sorbonne Universités, UPMC, Université Paris 06, UMR 7093, LOV, Observatoire Océanologique, 06230 Villefranche-sur-Mer, France Aix Marseille Université, CNRS/INSU, Université de Toulon, IRD, Mediterranean Institute of Oceanography (MIO) UM 110, 13288, Marseille, France.

Marine organic aggregates are sites of high of viral accumulation; however, still little is known about their colonization processes and interactions with their local bacterial hosts. By taking advantage of a novel approach (paramagnetic functionalized microsphere method) to create and incubate artificial macroaggregates, we examined the small-scale movements of viruses and bacteria between such marine snow particles and the surrounding water. The examination of the codynamics of both free-living and attached viral and bacterial abundance, over 12 hours of incubation in virus-free water, suggests that aggregates are rather comparable to viral factories than to viral traps where a significant part of the virions production might be locally diverted to the water column. Also, the near-zero proportion of lysogenized cells measured in aggregates after mitomycin-C induction seems to indicate that lysogeny is not a prominent viral reproduction pathway in organic aggregates where most viruses might rather be virulent. Finally, we hypothesize that, contrary to bacteria, which can use both strong attachment and detachment from aggregates (two-way motion of bacteria), the adsorption of planktonic viruses appears to be numerically negligible compared to their massive export from the aggregates into the water column (one-way motion of viruses).
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http://dx.doi.org/10.1093/femsle/fnv216DOI Listing
January 2016

Nutrient ratios and the complex structure of phytoplankton communities in a highly turbid estuary of Southeast Asia.

Environ Monit Assess 2014 Dec 10;186(12):8555-72. Epub 2014 Sep 10.

Institute of Marine Environment and Resources (IMER), Vietnam Academy of Science and Technology (VAST), Haiphong, Viet Nam.

Phytoplankton diversity and abundance in estuarine systems are controlled by many factors. Salinity, turbidity, and inorganic nutrient concentrations and their respective ratios have all been proposed as principal factors that structure phytoplankton diversity and influence the emergence of potentially toxic species. Although much work has been conducted on temperate estuaries, less is known about how phytoplankton diversity is controlled in tropical, monsoonal systems that are subject to large, seasonal shifts in hydrology and to rapidly changing land use. Here, we present the results of an investigation into the factors controlling phytoplankton species composition and distribution in a tropical, monsoonal estuary (Bach Dang estuary, North Vietnam). A total of 245 taxa, 89 genera from six algal divisions were observed. Bacillariophyceae were the most diverse group contributing to 51.4 % of the microalgal assemblage, followed by Dinophyceae (29.8 %), Chlorophyceae (10.2 %), Cyanophyceae (3.7 %), Euglenophyceae (3.7 %) and Dictyochophyceae (1.2 %). The phytoplankton community was structured by inorganic nutrient ratios (DSi:DIP and DIN:DIP) as well as by salinity and turbidity. Evidence of a decrease in phytoplankton diversity concomitant with an increase in abundance and dominance of certain species (e.g., Skeletonema costatum) and the appearance of some potentially toxic species over the last two decades was also found. These changes in phytoplankton diversity are probably due to a combination of land use change resulting in changes in nutrient ratios and concentrations and global change as both rainfall and temperature have increased over the last two decades. It is therefore probable in the future that phytoplankton diversity will continue to change, potentially favoring the emergence of toxic species in this system.
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http://dx.doi.org/10.1007/s10661-014-4024-yDOI Listing
December 2014

Fate and tidal transport of butyltin and mercury compounds in the waters of the tropical Bach Dang Estuary (Haiphong, Vietnam).

Mar Pollut Bull 2012 Sep 18;64(9):1789-98. Epub 2012 Jun 18.

Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, UMR 5254 IPREM, CNRS, Université de Pau et des Pays de l'Adour, 2 Avenue Président Pierre Angot, 64053 Pau, France.

In this work, two field campaigns were performed in July 2008 (wet season) and March 2009 (dry season) to produce original data on the concentration, partition and distribution of mercury and butyltin compounds along the tropical Bach Dang Estuary located in North Vietnam (Haiphong, Red River Delta). The results demonstrate that mercury and butyltin speciation in the surface waters of this type of tropical estuary is greatly affected by the drastic changes in the seasonal conditions. During high river discharge in the wet season, there was a large estuarine input of total Hg and tributyltin, while the longer residence time of the waters during the dry season promotes increasing MMHg formation and TBT degradation. Although most of the Hg and TBT is transported into the estuary from upstream sources, tidal cycle measurements demonstrate that this estuary is a significant source of TBT and MMHg during the wet (~3 kg TBT/day) and dry (~3 g MMHg/day) seasons.
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http://dx.doi.org/10.1016/j.marpolbul.2012.05.036DOI Listing
September 2012

A preliminary study on metal and nutrient concentrations in running water systems in southern New Caledonia.

Bull Environ Contam Toxicol 2011 Oct 24;87(4):361-5. Epub 2011 Jul 24.

Laboratoire d'Océanographie de Villefranche, Université Pierre et Marie Curie, UMR 7093, 06230 Villefranche-sur-Mer, France.

Metal and nutrient concentrations were measured in five running water sampling sites of New Caledonia. Metal concentrations were homogeneous (Ni; 22.7-50.6 μg L(-1)) or not (Fe; 37-749 μg L(-1)). Concentrations of Ni, Cr, Fe were high, including high dissolved fractions (up to 47.8, 70.8 and 417 μg L(-1), respectively). Concentrations of anthropogenic metals (Ag, As, Cd, Cu, Pb, Sb, V, Zn) were low (maximum: total Cu, 0.6 μg L(-1)). The contamination of waters is presumably due to soil weathering and mining activities. Metal concentrations and phosphate depletion (<0.04 μmol L(-1)) suggest constrained conditions for the development of aquatic life.
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http://dx.doi.org/10.1007/s00128-011-0367-zDOI Listing
October 2011

Viral distribution and life strategies in the Bach Dang Estuary, Vietnam.

Microb Ecol 2011 Jul 9;62(1):143-54. Epub 2011 Mar 9.

UMR 5119, ECOSYM, Montpellier 2 University, CNRS, IRD, IFREMER, Montpellier, France.

Although the structure and dynamics of planktonic viruses in freshwater and seawater environments are relatively well documented, little is known about the occurrence and activity of these viruses in estuaries, especially in the tropics. Viral abundance, life strategies, and morphotype distribution were examined in the Bach Dang Estuary (Vietnam) during the dry season in 2009. The abundance of both viruses and their prokaryotic hosts decreased significantly from upstream to downstream, probably as the result of nutrient dilution and osmotic stress faced by the freshwater communities. The antibiotic mitomycin-C revealed that the fraction of lysogenic cells was substantially higher in the lower seawater part of the estuary (max 27.1%) than in the upper freshwater area where no inducible lysogens were observed. The question of whether there is a massive, continuous induction of marine lysogens caused by the mixing with freshwater is considered. Conversely, the production of lytic viruses declined as salinity increased, indicating a spatial succession of viral life strategies in this tropical estuary. Icosahedral tailless viruses with capsids smaller than 60 nm dominated the viral assemblage throughout the estuary (63.0% to 72.1% of the total viral counts), and their distribution was positively correlated with that of viral lytic production. Interestingly, the gamma-proteobacteria explained a significant portion of the variance in the <60 nm and 60 to 90 nm tailless viruses (92% and 80%, respectively), and in the Myoviridae (73%). Also, 60% of the variance of the tailless larger viruses (>90 nm) was explained by the beta-proteobacteria. Overall, these results support the view that the environment, through selection mechanisms, probably shapes the structure of the prokaryotic community. This might be in turn a source of selection for the virioplankton community via specific affiliation favoring particular morphotypes and life strategies.
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http://dx.doi.org/10.1007/s00248-011-9835-6DOI Listing
July 2011

Virus attachment to transparent exopolymeric particles along trophic gradients in the southwestern lagoon of New Caledonia.

Appl Environ Microbiol 2007 Aug 22;73(16):5245-52. Epub 2007 Jun 22.

IRD, Noumea Center, BP A5, NC-98848 Noumea, New Caledonia.

Viruses on organic aggregates such as transparent exopolymeric particles (TEP) are not well investigated. The number of TEP-attached viruses was assessed along trophic gradients in the southwestern lagoon of New Caledonia by determining the fraction of viruses removed after magnetic isolation of TEP. In order to isolate TEP magnetically, TEP were formed in the presence of magnetic beads from submicrometer precursors collected along the trophic gradients. The mixed aggregates of TEP-beads-viruses were removed from solution with a magnetic field. The percentage of viruses associated with newly formed TEP averaged 8% (range, 3 to 13%) for most of the stations but was higher (ca. 30%) in one bay characterized by the low renewal rate of its water mass. The number of viruses (N) attached to TEP varied as a function of TEP size (d [in micrometers]) according to the formulas N = 100d(1.60) and N = 230d(1.75), respectively, for TEP occurring in water masses with short (i.e., <40 days) and long (i.e., >40 days) residence times. These two relationships imply that viral abundance decreases with TEP size, and they indicate that water residence time influences viral density and virus-bacterium interactions within aggregates. Our data suggest that the fraction of viruses attached to TEP is highest in areas characterized by a low renewal rate of the water mass and can constitute at times a significant fraction of total virus abundance. Due to the small distance between viruses and hosts on TEP, these particles may be hot spots for viral infection.
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http://dx.doi.org/10.1128/AEM.00762-07DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1950989PMC
August 2007

Coupling between autocatalytic cell death and transparent exopolymeric particle production in the marine cyanobacterium Trichodesmium.

Environ Microbiol 2007 Jun;9(6):1415-22

Mina and Everard Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, 52900, Israel.

Extracellular polysaccharide aggregates, operationally defined as transparent exopolymeric particles (TEP), are recognized as an important conduit for carbon recycling and export in aquatic systems. Yet, the factors controlling the build-up of the TEP pool are not well characterized. Here we show that increased TEP production by Trichodesmium, an oceanic bloom-forming nitrogen-fixing (diazotrophic) cyanobacterium, is coupled with autocatalytic programmed cell death (PCD) process. We demonstrate that PCD induction, in both laboratory cultures and natural populations, is characterized by high caspase-like activity, correlates with enhanced TEP production, and occurs under iron and phosphorus starvation, as well as under high irradiance and oxidative stress. Enhanced TEP production was not observed in actively growing populations. We provide further evidence that iron is a key trigger for the induction of PCD. We demonstrate, for the first time, the concomitant enhanced build-up of the TEP pool when Trichodesmium is Fe-stressed. These results suggest a functional linkage between activation of caspases and PCD in Trichodesmium and regulation of vertical carbon and nitrogen fluxes. We hypothesize that modulation of TEP formation and its qualities by different mortality pathways could regulate the fate of phytoplankton blooms and particulate organic matter in aquatic ecosystems.
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http://dx.doi.org/10.1111/j.1462-2920.2007.01257.xDOI Listing
June 2007
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