Publications by authors named "Dong-Feng Liu"

35 Publications

Recovery of Iron-Dependent Autotrophic Denitrification Activity from Cell-Iron Mineral Aggregation-Induced Reversible Inhibition by Low-Intensity Ultrasonication.

Environ Sci Technol 2022 Jan 21;56(1):595-604. Epub 2021 Dec 21.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei 230026, China.

Iron-dependent autotrophic denitrification (IDAD) has garnered increasing interests as an efficient method for removing nitrogen from wastewater with a low carbon to nitrogen ratio. However, an inevitable deterioration of IDAD performance casts a shadow over its further development. In this work, the hidden cause for such a deterioration is uncovered, and a viable solution to this problem is provided. Batch test results reveal that the aggregation of microbial cells and iron-bearing minerals induced a cumulative and reversible inhibition on the activity of IDAD sludge. Extracellular polymeric substances were found to play a glue-like role in the cell-iron mineral aggregates, where microbial cells were caged, and their metabolisms were suppressed. Adopting low-intensity ultrasound treatment efficiently restored the IDAD activity by disintegrating such aggregates rather than stimulating the microbial metabolism. Moreover, the ultrasonication-assisted IDAD bioreactor exhibited an advantageous nitrogen removal efficiency (with a maximum enhancement of 72.3%) and operational stability compared to the control one, demonstrating a feasible strategy to achieve long-term stability of the IDAD process. Overall, this work provides a better understanding about the mechanism for the performance deterioration and a simple approach to maintain the stability of IDAD.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.est.1c05553DOI Listing
January 2022

Controlling pathogenic risks of water treatment biotechnologies at the source by genetic editing means.

Environ Microbiol 2021 Dec 27;23(12):7578-7590. Epub 2021 Nov 27.

CAS Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, China.

Antimicrobial-resistant pathogens in the environment and wastewater treatment systems, many of which are also important pollutant degraders and are difficult to control by traditional disinfection approaches, have become an unprecedented treat to ecological security and human health. Here, we propose the adoption of genetic editing techniques as a highly targeted, efficient and simple tool to control the risks of environmental pathogens at the source. An 'all-in-one' plasmid system was constructed in Aeromonas hydrophila to accurately identify and selectively inactivate multiple key virulence factor genes and antibiotic resistance genes via base editing, enabling significantly suppressed bacterial virulence and resistance without impairing their normal phenotype and pollutant-degradation functions. Its safe application for bioaugmented treatment of synthetic textile wastewater was also demonstrated. This genetic-editing technique may offer a promising solution to control the health risks of environmental microorganisms via targeted gene inactivation, thereby facilitating safer application of water treatment biotechnologies.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/1462-2920.15851DOI Listing
December 2021

Engineering of salt-tolerant Shewanella aquimarina XMS-1 for enhanced pollutants transformation and electricity generation.

Sci Total Environ 2022 Feb 15;807(Pt 3):151009. Epub 2021 Oct 15.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science & Technology of China, Hefei 230026, China. Electronic address:

Saline wastewater poses a challenge during bio-treatment process due to salinity affecting the physiological activity of microorganisms and inhibiting their growth and metabolism. Thus, screening and engineering the salt-tolerant strains with stronger performances are urgent. Shewanella aquimarina XMS-1, a salt-tolerant dissimilated metal reducing bacteria (DMRB), was isolated from seawater environment. Its ability for reducing pollutants and generating electricity was enhanced by overexpression of riboflavin synthesis pathway encoding genes from S. oneidensis MR-1 under salt stress. Furthermore, upon contact with graphene oxide (GO), the engineered strain XMS-1/pYYDT-rib with enhanced flavins synthesis could reduce GO and self-assemble to form a three-dimensional (3D) biohybrid system named XMS-1/flavins/rGO. This 3D biohybrid system significantly enhanced the EET efficiency of S. aquimarina XMS-1. Our findings provide a feasible strategy for treatment of salt-containing industrial wastewater contaminated by metal and organic pollutants.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.scitotenv.2021.151009DOI Listing
February 2022

Extracellular electron transfer via multiple electron shuttles in waterborne Aeromonas hydrophila for bioreduction of pollutants.

Biotechnol Bioeng 2021 12 27;118(12):4760-4770. Epub 2021 Sep 27.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei, China.

Members of the genus Aeromonas prevail in aquatic habitats and have a great potential in biological wastewater treatment because of their unique extracellular electron transfer (EET) capabilities. However, the mediated EET mechanisms of Aeromonas have not been fully understood yet, hindering their applications in biological wastewater treatment processes. In this study, the electron shuttles in Aeromonas hydrophila, a model and widespread strain in aquatic environments and wastewater treatment plants, were explored. A. hydrophila was found to produce both flavins and 2-amino-3-carboxy-1,4-naphthoquinone (ACNQ) as electron shuttles and utilize them to accelerate its EET for the bioreduction of various pollutants. The Mtr-like respiratory pathway was essential for the reduction of flavins, but not involved in the ACNQ reduction. The electron shuttle activity of ACNQ for pollutant bioreduction involved the redox reactions that occurred inside the cell. These findings deepen our understanding about the underlying EET mechanisms in dissimilatory metal reducing bacteria and provide new insights into the roles of the genus Aeromonas in biological wastewater treatment.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/bit.27940DOI Listing
December 2021

Unexpected Discovery of Hypermutator Phenotype Sounds the Alarm for Quality Control Strains.

Genome Biol Evol 2021 Aug;13(8)

Institute of Evolution and Marine Biodiversity, KLMME, Ocean University of China, Qingdao, China.

Microbial strains with high genomic stability are particularly sought after for testing the quality of commercial microbiological products, such as biological media and antibiotics. Yet, using mutation-accumulation experiments and de novo assembled complete genomes based on Nanopore long-read sequencing, we find that the widely used quality-control strain Shewanella putrefaciens ATCC-8071, also a facultative pathogen, is a hypermutator, with a base-pair substitution mutation rate of 2.42 × 10-8 per nucleotide site per cell division, ∼146-fold greater than that of the wild-type strain CGMCC-1.6515. Using complementation experiments, we confirm that mutL dysfunction, which was a recent evolutionary event, is the cause for the high mutation rate of ATCC-8071. Further analyses also give insight into possible relationships between mutation and genome evolution in this important bacterium. This discovery of a well-known strain being a hypermutator necessitates screening the mutation rate of bacterial strains before any quality control or experiments.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/gbe/evab148DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8350357PMC
August 2021

Phosphorus Recovery from Wastewater Prominently through a Fe(II)-P Oxidizing Pathway in the Autotrophic Iron-Dependent Denitrification Process.

Environ Sci Technol 2020 09 28;54(18):11576-11583. Epub 2020 Aug 28.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei 230026, China.

Phosphorus (P) recovery from wastewater can be completed by iron-involved autotrophic denitrification via forming Fe(III)-P precipitates and/or adsorbing P onto Fe(III) oxyhydroxides. However, so far, most studies focused on the final P-containing products, while the P-capturing pathways in such a process remain unclear. In this work, autotrophic iron-dependent denitrification (AIDD) was used as a typical anoxic iron-involved P-capturing biosystem to investigate the main P recovery pathways. The AIDD biosystem showed a relatively stable capability of capturing P coupled with nitrate reduction. Direct formation of amorphous Fe(II)-P precipitates after the phosphate was fed, followed by microbially driven oxidation into Fe(III)-P minerals, was found to be the primary pathway for the P capture. In addition, adsorption of phosphate onto the formed iron oxyhydroxides also contributed to the P recovery. This work provides better understanding about recovering P in AIDD and iron-involved denitrification and highlights the important roles of iron oxidizers in the iron-related biological wastewater treatment processes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.est.0c02882DOI Listing
September 2020

Potential-dependent extracellular electron transfer pathways of exoelectrogens.

Curr Opin Chem Biol 2020 12 5;59:140-146. Epub 2020 Aug 5.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei 230026, China; USTC-City U Joint Advanced Research Center, Suzhou 215123, China. Electronic address:

Exoelectrogens are distinct from other bacteria owing to their unique extracellular electron transfer (EET) abilities that allow for anaerobic respiration with various external redox-active surfaces, including electrode and metal oxides. Although the EET process is known to trigger diverse extracellular redox reactions, the reverse impact has been long overlooked. Recent evidences show that exoelectrogens can sense the potential changes of external surfaces and alter their EET strategies accordingly, which imparts them remarkable abilities in adapting to diverse and redox-variable environment. This mini-review provides a condensed overview and critical analysis about the recent discoveries on redox-dependent EET pathways of exoelectrogens, with focus on Geobacter sulfurreducens and Shewanella oneidensis. We summarize the detailed responses of various EET components, analyze the drives and mechanisms of such responses, highlight the diversity of EET dynamics among different bacterial species and under integrated effects of redox potential and surface chemistry, and discusses the future research needs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.cbpa.2020.06.005DOI Listing
December 2020

Dependence of arsenic resistance and reduction capacity of Aeromonas hydrophila on carbon substrate.

J Hazard Mater 2021 02 3;403:123611. Epub 2020 Aug 3.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei, 230026, China.

The high toxicity and prevalence of arsenic in the environment have aroused increasing research interest in understanding the mechanisms of microbial arsenic resistance. A wide spectrum of arsenic resistant microbes with ability of arsenic bio-transformation has been isolated from arsenic-contaminated environments. However, arsenic resistance processes and reduction abilities of microbes under various growth conditions remain poorly understood. In this work, a high correlation between the arsenic resistance and reduction ability of Aeromonas hydrophila and the carbon substrate was identified. Genome analysis suggests that the arsenic resistance system is widely present in Aeromonas genus, and the arsenic resistance was associated with the ars operon. The sensitivity of A. hydrophila to As(V) and As(III) depended heavily on the type of carbon substrate. The upregulated expression of arsA, arsB, arsD and/or downregulated expression of glpF might be responsible for the increased microbial tolerance to As(III). The As(V) reduction rate was also affected by the type of carbon substrate. Our results provide new insights into the impacts of carbon substrate on the arsenic biotoxicity as well as arsenic biotransformation processes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jhazmat.2020.123611DOI Listing
February 2021

Developing a base-editing system to expand the carbon source utilization spectra of Shewanella oneidensis MR-1 for enhanced pollutant degradation.

Biotechnol Bioeng 2020 08 14;117(8):2389-2400. Epub 2020 May 14.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei, China.

Shewanella oneidensis MR-1, a model strain of exoelectrogenic bacteria (EEB), plays a key role in environmental bioremediation and bioelectrochemical systems because of its unique respiration capacity. However, only a narrow range of substrates can be utilized by S. oneidensis MR-1 as carbon sources, resulting in its limited applications. In this study, a rapid, highly efficient, and easily manipulated base-editing system pCBEso was developed by fusing a Cas9 nickase (Cas9n (D10A)) with the cytidine deaminase rAPOBEC1 in S. oneidensis MR-1. The C-to-T conversion of suitable C within the base-editing window could be readily and efficiently achieved by the pCBEso system without requiring double-strand break or repair templates. Moreover, double-locus simultaneous editing was successfully accomplished with an efficiency of 87.5%. With this tool, the key genes involving in N-acetylglucosamine (GlcNAc) or glucose metabolism in S. oneidensis MR-1 were identified. Furthermore, an engineered strain with expanded carbon source utilization spectra was constructed and exhibited a higher degradation rate for multiple organic pollutants (i.e., azo dyes and organoarsenic compounds) than the wild-type when glucose or GlcNAc was used as the sole carbon source. Such a base-editing system could be readily applied to other EEB. This study not only enhances the substrate utilization and pollutant degradation capacities of S. oneidensis MR-1 but also accelerates the robust construction of engineered strains for environmental bioremediation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/bit.27368DOI Listing
August 2020

Deteriorated biofilm-forming capacity and electroactivity of Shewanella oneidnsis MR-1 induced by insertion sequence (IS) elements.

Biosens Bioelectron 2020 May 9;156:112136. Epub 2020 Mar 9.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei, 230026, China. Electronic address:

Shewanella oneidensis MR-1, a model species of exoelectrogenic bacteria (EEB), has been widely applied in bioelectrochemical systems. Biofilms of EEB grown on electrodes are essential in governing the current output and power density of bioelectrochemical systems. The MR-1 genome is exceptionally dynamic due to the existence of a large number of insertion sequence (IS) elements. However, to date, the impacts of IS elements on the biofilm-forming capacity of EEB and performance of bioelectrochemical systems remain unrevealed. Herein, we isolated a non-motile mutant (NMM) with biofilm-deficient phenotype from MR-1. We found that the insertion of an ISSod2 element into the flrA (encoding the master regulator for flagella synthesis and assembly) of MR-1 resulted in the non-motile and biofilm-deficient phenotypes in NMM cells. Notably, such a variant was readily confused with the wild-type strain because there were no obvious differences in growth rates and colonial morphologies between the two strains. However, the reduced biofilm formation on the electrodes and the deteriorated performances of bioelectrochemical systems and Cr(VI) immobilization for the strain NMM were observed. Given the wide distribution of IS elements in EEB, appropriate cultivation and preservation conditions should be adopted to reduce the likelihood that IS elements-mediated mutation occurs in EEB. These findings reveal the negative impacts of IS elements on the biofilm-forming capacity of EEB and performance of bioelectrochemical systems and suggest that great attention should be given to the actual physiological states of EEB before their applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.bios.2020.112136DOI Listing
May 2020

CRISPRi System as an Efficient, Simple Platform for Rapid Identification of Genes Involved in Pollutant Transformation by .

Environ Sci Technol 2020 03 5;54(6):3306-3315. Epub 2020 Mar 5.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science & Technology of China, Hefei, 230026, P. R. China.

species are indigenous in diverse aquatic environments and play important roles in environmental remediation. However, the pollutant transformation mechanisms of these bacteria remain elusive, and their potential in pollution control is largely unexploited so far. In this work, we report an efficient and simple genome regulation tool to edit and identify its biomolecular pathways for pollutant transformation. The genome regulation system, which is based on the type II clustered regularly interspaced short palindromic repeat interference (CRISPRi) system from , can serve as a reversible and multiplexible platform for gene knockdown in . A single-plasmid CRISPRi system harboring both dCas9 and the sgRNA was constructed in and used to silence diverse genes with varied sizes and expression levels. With this system, up to 467-fold repression of expression was achieved, and the function of the essential gene- was identified quickly and accurately. Furthermore, simultaneous transcriptional repression of multiple targeted genes was realized. We discovered that the operon played an essential role in arsenic detoxification, and the extracellular electron transfer (EET) pathway was involved in methyl orange reduction, but not in vanadium reduction by . Our method allows better insights and effective genetic manipulation of the pollutant transformation processes in , which might facilitate more efficient utilization of the species and other microbial species for environmental remediation applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.est.9b07191DOI Listing
March 2020

Promoting bidirectional extracellular electron transfer of Shewanella oneidensis MR-1 for hexavalent chromium reduction via elevating intracellular cAMP level.

Biotechnol Bioeng 2020 05 18;117(5):1294-1303. Epub 2020 Feb 18.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science & Technology of China, Hefei, China.

The bioreduction capacity of Cr(VI) by Shewanella is mainly governed by its bidirectional extracellular electron transfer (EET). However, the low bidirectional EET efficiency restricts its wider applications in remediation of the environments contaminated by Cr(VI). Cyclic adenosine 3',5'-monophosphate (cAMP) commonly exists in Shewanella strains and cAMP-cyclic adenosine 3',5'-monophosphate receptor protein (CRP) system regulates multiple bidirectional EET-related pathways. This inspires us to strengthen the bidirectional EET through elevating the intracellular cAMP level in Shewanella strains. In this study, an exogenous gene encoding adenylate cyclase from the soil bacterium Beggiatoa sp. PS is functionally expressed in Shewanella oneidensis MR-1 (the strain MR-1/pbPAC) and a MR-1 mutant lacking all endogenous adenylate cyclase encoding genes (the strain Δca/pbPAC). The engineered strains exhibit the enhanced bidirectional EET capacities in microbial electrochemical systems compared with their counterparts. Meanwhile, a three times more rapid reduction rate of Cr(VI) is achieved by the strain MR-1/pbPAC than the control in batch experiments. Furthermore, a higher Cr(VI) reduction efficiency is also achieved by the strain MR-1/pbPAC in the Cr(VI)-reducing biocathode experiments. Such a bidirectional enhancement is attributed to the improved production of cAMP-CRP complex, which upregulates the expression levels of the genes encoding the c-type cytochromes and flavins synthetic pathways. Specially, this strategy could be used as a broad-spectrum approach for the other Shewanella strains. Our results demonstrate that elevating the intracellular cAMP levels could be an efficient strategy to enhance the bidirectional EET of Shewanella strains and improve their pollutant transformation capacity.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/bit.27305DOI Listing
May 2020

Exclusive microbially driven autotrophic iron-dependent denitrification in a reactor inoculated with activated sludge.

Water Res 2020 Mar 13;170:115300. Epub 2019 Nov 13.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei, 230026, China; School of Resources & Environmental Engineering, Hefei University of Technology, Hefei, 230009, China. Electronic address:

Autotrophic iron-dependent denitrification (AIDD) is arising as a promising process for nitrogen removal from wastewater with a low carbon to nitrogen ratio. However, there is still a debate about the existence of such a process in activated sludge systems. This work provides evidence and elucidated the feasibility of autotrophic Fe(II)-oxidizing nitrate-reducing culture for nitrogen removal by long-term reactor operation, batch experimental verification, unstructured kinetic modeling and microbial community analyses. A relatively stable nitrate removal rate was achieved coupled with the oxidation of ferrous ions in 3-month operation of reactor. The kinetic modeling suggests that the iron oxidation was a growth-associated process in AIDD. Utilization of extracellular polymeric substances (and/or soluble microbial products) as electron donor for denitrification by heterotrophic denitrifiers was not mainly responsible for nitrogen removal in the reactor. After long-term operation of the reactor with activated sludge as inoculum, the enrichment culture KS-like consortium, dominated by Fe(II) oxidizer, Gallionellaceae, was successfully acclimated for autotrophic Fe(II)-oxidizing nitrate reduction. This work extents our understanding about the existence of such an autotrophic Fe(II)-oxidizing nitrate-reducing culture in both natural and engineered systems, and opens a door for its potential application in wastewater treatment.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.watres.2019.115300DOI Listing
March 2020

Sensing and Approaching Toxic Arsenate by CN-32.

Environ Sci Technol 2019 12 5;53(24):14604-14611. Epub 2019 Dec 5.

Although arsenic at a high concentration imposes strong selective pressure on microbes, various microbes have been found to grow in As-rich environments. So far, little is known about how microbes can sense and move toward arsenate in the environment, and the underlying molecular mechanisms have not been revealed. Here, we report the chemotaxis response toward arsenate (As(V)) by CN-32, a model dissimilatory metal-reducing bacterium (DMRB), and elucidate the mechanisms. We find that CN-32 exhibits a chemotactic behavior toward As(V) and diverse electron acceptors. To sense As(V), CN-32 requires functional arsenate respiratory reductase but does not depend on its metal-reducing-like respiratory pathway. We observe that such a sense is governed by an energy taxis mechanism and mediated by several methyl-accepting chemotaxis proteins (MCPs), rather than a specific MCP. Moreover, we reveal that the chemotactic signal transduction pathway is conserved in , and histidine kinase and flagella-mediated motility are essential for taxis toward As(V). This work reverses the conventional view about arsenic as a chemotactic inhibitor to microbes by revealing the positive chemotaxis of to As(V).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.est.9b05890DOI Listing
December 2019

Isolation and characterization of a chlorate-reducing bacterium Ochrobactrum anthropi XM-1.

J Hazard Mater 2019 12 12;380:120873. Epub 2019 Jul 12.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science & Technology of China, Hefei, 230026, China.

A Gram-negative chlorate-reducing bacterial strain XM-1 was isolated. The 16S rRNA gene sequence identified the isolate as Ochrobactrum anthropi XM-1, which was the first strain of genus Ochrobactrum reported having the ability to reduce chlorate. The optimum growth temperature and pH for strain XM-1 to reduce chlorate was found to be 30 °C and 5.0-7.5, respectively, under anaerobic condition. Strain XM-1 could tolerate high chlorate concentration (200 mM), and utilize a variety of carbohydrates (glucose, L-arabinose, D-fructose, sucrose), glycerin and sodium citrate as electron donors. In addition, oxygen and nitrate could be used as electron acceptors, but perchlorate could not be reduced. Enzyme activities related to chlorate reducing were characterized in cell extracts. Activities of chlorate reductase and chlorite dismutase could be detected in XM-1 cells grown under both aerobic and anaerobic conditions, implying the two enzymes were constitutively expressed. This work suggests a high potential of applying Ochrobactrum anthropi XM-1 for remediation of chlorate contamination.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jhazmat.2019.120873DOI Listing
December 2019

Formation mechanism of organo-chromium (III) complexes from bioreduction of chromium (VI) by Aeromonas hydrophila.

Environ Int 2019 08 20;129:86-94. Epub 2019 May 20.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei 230026, China. Electronic address:

Chromium is a common heavy metal widely present in aquatic environments. Cost-effective remediation of chromium-contaminated environment can be realized by microbial reduction of Cr(VI) to Cr(III). The genus Aeromonas species is one of such Cr(VI) reducers, whose reduction mechanism remains unrevealed and the main factors governing the Cr(VI) reduction pathways are unknown yet. In this work, the performances and mechanisms of Cr(VI) anaerobic reduction by Aeromonas hydrophila ATCC 7966 were investigated. This strain exhibited excellent Cr(VI) resistance and could utilize a suite of electron donors to support Cr(VI) bioreduction. The Cr(VI) bioreduction processes involved both extracellular (the metal-reducing and respiratory pathway) and intracellular reaction pathways. Adding anthraquinone-2,6-disulfonate or humic acid as a mediator substantially enhanced the Cr(VI) bioreduction. The forms and distribution of the Cr(VI) bioreduction products were affected by the medium composition. Soluble organo-Cr(III) complexes were identified as the main Cr(VI) reduction products when basal salts medium was adopted. Given the environmental ubiquity of the genus Aeromonas, the findings in this work may facilitate a better understanding about the transformation behaviors and fates of Cr(VI) in environments and provide useful clues to tune the bioremediation of chromium-contaminated environments.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.envint.2019.05.016DOI Listing
August 2019

Mediation of functional gene and bacterial community profiles in the sediments of eutrophic Chaohu Lake by total nitrogen and season.

Environ Pollut 2019 Jul 10;250:233-240. Epub 2019 Apr 10.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science & Technology of China, Hefei, 230026, China. Electronic address:

Microbes in sediments contribute to nutrient release and play an important role in lake eutrophication. However, information about the profiles of functional genes and bacterial communities and the most important environmental factor affecting them in the sediments of eutrophic lake remains unrevealed. In this work, the real-time fluorescent quantitative polymerase chain reaction (qPCR) assay and 16S ribosomal RNA gene next generation sequencing analysis were used to explore the profiles of functional genes and bacterial communities in the sediments of Chaohu Lake. The selected 18 functional genes involved in C, N and P cycles were detected in most of samples. Seasonal variation and sediment variables were found to affect the profiles of functional genes and bacterial communities, and total nitrogen was the dominant environmental factor to drive the formation of bacterial community structure. Proteobacteria and Firmicutes were observed to be the two dominant phyla in the sediments with relative abundance ranging from 10.8% to 36.0% and 7.7%-46.7%, respectively. Three bacterial phyla, i.e., Actinobacteria, Proteobacteria, and Spirochaetes, were found to be significantly positively correlated with the C, N and P-cycle related functional genes. Bacterial community structure was the most important driver to shape the profiles of functional genes. Seasonal variation also influenced the co-occurrence patterns between functional genes and bacterial taxa as revealed by network analysis. The findings from this work facilitate a better understanding about the C, N, and P cycles in the sediments of eutrophic lakes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.envpol.2019.04.028DOI Listing
July 2019

Potential regulates metabolism and extracellular respiration of electroactive Geobacter biofilm.

Biotechnol Bioeng 2019 05 11;116(5):961-971. Epub 2019 Feb 11.

Department of Applied Chemistry, University of Science and Technology of China, Hefei, China.

Dissimilatory metal reducer Geobacter sulfurreducens can mediate redox processes through extracellular electron transfer and exhibit potential-dependent electrochemical activity in biofilm. Understanding the microbial acclimation to potential is of critical importance for developing robust electrochemically active biofilms and facilitating their environmental, geochemical, and energy applications. In this study, the metabolism and redox conduction behaviors of G. sulfurreducens biofilms developed at different potentials were explored. We found that electrochemical acclimation occurred at the initial hours of polarizing G. sulfurreducens cells to the potentials. Two mechanisms of acclimation were found, depending on the polarizing potential. In the mature biofilms, a low level of biosynthesis and a high level of catabolism were maintained at +0.2 V versus standard hydrogen electrode (SHE). The opposite results were observed at potentials higher than or equal to +0.4 V versus SHE. The potential also regulated the constitution of the electron transfer network by synthesizing more extracellular cytochrome c such as OmcS at 0.0 and +0.2 V and exhibited a better conductivity. These findings provide reasonable explanations for the mechanism governing the electrochemical respiration and activity in G. sulfurreducens biofilms.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/bit.26928DOI Listing
May 2019

Synthesis of CdSSe quantum dots in a protozoa Tetrahymena pyriformis.

Appl Microbiol Biotechnol 2019 Jan 11;103(2):973-980. Epub 2018 Nov 11.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei, 230026, China.

Quantum dots (QDs) are recognized as the excellent fluorescence and photochemical materials to be applied in bioimaging, biomedical, and solar cell fields. Biosynthesized QDs (bio-QDs) have attracted attention due to their simple, eco-friendly, and excellent biocompatible traits. Moreover, bio-QDs could not be replaced by chemically fabricated QDs in many fields. Bio-QDs synthesized by different microorganisms have diverse characteristics. In this work, the biosynthesis of QDs by Tetrahymena pyriformis, a typical protozoa in aquatic environments, was achieved for the first time. The synthesized materials by T. pyriformis emitted yellow fluorescence and had an average diameter of 8.27 ± 0.77 nm. Spectral characterization results demonstrated that the synthesized QDs were CdSSe. Meanwhile, the fluorescence intensities of the synthesized bio-QDs showed a linear relationship with Cd dosage ranging from 20 to 80 μM. The fluorescence enhancement of the synthesized QDs was highly selective to Cd compared to other metal ions. The bio-QDs were demonstrated to have a great potential to be applied for Cd detection. This work provides valuable information about the transformation of heavy metal ions in protozoan and is useful to accelerate the applications of the synthesized QDs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s00253-018-9499-yDOI Listing
January 2019

Abundance and diversity of iron reducing bacteria communities in the sediments of a heavily polluted freshwater lake.

Appl Microbiol Biotechnol 2018 Dec 17;102(24):10791-10801. Epub 2018 Oct 17.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science & Technology of China, Hefei, 230026, China.

Iron reduction mediated by Fe(III)-reducing bacteria (FeRB) occurs in aqueous environments and plays an essential role in removing contaminates in polluted freshwater lakes. Two model FeRB species, Shewanella and Geobacter, have been intensively studied because of their functions in bioremediation, iron reduction, and bioelectricity production. However, the abundance and community diversity of Shewanella and Geobacter in eutrophic freshwater lakes remain largely unknown. In this work, the distribution, abundance and biodiversity of Shewanella, Geobacter and other FeRB in the sediments of a heavily polluted lake, Chaohu Lake, China, across four successive seasons were investigated. Shewanella, Geobacter, and other FeRB were found to be widely distributed in the sediment of this heavily eutrophic lake. Geobacter was abundant with at least one order of magnitude more than Shewanella in cold seasons. Three Shewanella-related operational taxonomic units were detected and sixty one Geobacter-related operational taxonomic units were grouped into three phylogenetic clades. Thiobacillus, Desulfuromonas and Geobacter were identified as the main members of FeRB in the lake sediments. Interestingly, nutrients like carbon, nitrogen, and phosphorus were found to be the key factors governing the abundance and diversity of FeRB. Total FeRB, as well as Geobacter and Shewanella, were more abundant in the heavily eutrophic zone than those in the lightly eutrophic zone. The abundance and diversity of FeRB in the sediments of freshwater lakes were highly related with the degree of eutrophication, which imply that FeRB might have a great potential in alleviating the eutrophication and contamination in aqueous environments.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s00253-018-9443-1DOI Listing
December 2018

Continuous degradation of ciprofloxacin in a manganese redox cycling system driven by Pseudomonas putida MnB-1.

Chemosphere 2018 Nov 31;211:345-351. Epub 2018 Jul 31.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China. Electronic address:

Ciprofloxacin (CIP), as an extensively used antibiotic, has been widely detected at a high level in the environment and has raised environmental pollution concerns. Thus, efficient and cost-effective methods for CIP degradation are highly desired. Biologically produced manganese oxides (BioMnO) offer a promising perspective for CIP degradation because of their catalytic reactivity and cost-effectiveness. However, the release of Mn(II) from BioMnO prevents the further oxidation of pollutants. As a consequence, continuous CIP degradation by BioMnO is not feasible. In this work, a manganese redox cycling system driven by Pseudomonas putida MnB-1 was constructed for continuous degradation of CIP. In such a system CIP was oxidized continuously and rapidly by re-oxidizing the formed Mn(II) to regenerate reactive BioMnO, which also protected the strain from CIP toxicity. CIP was degraded through N-dealkylation passway. No significant loss of BioMnO reactivity was observed in three-cycle CIP degradation process, suggesting the stability of this system. An overlooked intracellular BioMnO, which was involved in CIP degradation, was discovered in P. putida MnB-1. Moreover, the important role of Mn(III) in facilitating CIP removal in this system was also identified. This work provides useful information to better understand the degradation of antibiotic compounds mediated by microbes in environments.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.chemosphere.2018.07.117DOI Listing
November 2018

Estimates of abundance and diversity of Shewanella genus in natural and engineered aqueous environments with newly designed primers.

Sci Total Environ 2018 Oct 12;637-638:926-933. Epub 2018 May 12.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science & Technology of China, Hefei 230026, China. Electronic address:

Shewanella species have a diverse respiratory ability and wide distribution in environments and play an important role in bioremediation and the biogeochemical cycles of elements. Primers with more accuracy and broader coverage are required with consideration of the increasing number of Shewanella species and evaluation of their roles in various environments. In this work, a new primer set of 640F/815R was developed to quantify the abundance of Shewanella species in natural and engineered environments. In silico tools for primer evaluation, quantitative polymerase chain reaction (qPCR) and clone library results showed that 640F/815R had a higher specificity and coverage than the previous primers in quantitative analysis of Shewanella. Another newly developed primer pair of 211F/815cR was also adopted to analyze the Shewanella diversity and demonstrated to be the best candidate in terms of specificity and coverage. We detected more Shewanella-related species in freshwater environments and found them to be substantially different from those in marine environments. Abundance and diversity of Shewanella species in wastewater treatment plants were largely affected by the process and operating conditions. Overall, this study suggests that investigations of abundance and diversity of Shewanella in various environments are of great importance to evaluate their ecophysiology and potential ecological roles.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.scitotenv.2018.05.051DOI Listing
October 2018

Directed Biofabrication of Nanoparticles through Regulating Extracellular Electron Transfer.

J Am Chem Soc 2017 09 24;139(35):12149-12152. Epub 2017 Aug 24.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China , Hefei 230026, China.

Biofabrication of nanomaterials is currently constrained by a low production efficiency and poor controllability on product quality compared to chemical synthetic routes. In this work, we show an attractive new biosynthesis system to break these limitations. A directed production of selenium-containing nanoparticles in Shewanella oneidensis MR-1 cells, with fine-tuned composition and subcellular synthetic location, was achieved by modifying the extracellular electron transfer chain. By taking advantage of its untapped intracellular detoxification and synthetic power, we obtained high-purity, uniform-sized cadmium selenide nanoparticles in the cytoplasm, with the production rates and fluorescent intensities far exceeding the state-of-the-art biosystems. These findings may fundamentally change our perception of nanomaterial biosynthesis process and lead to the development of fine-controllable nanoparticles biosynthesis technologies.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jacs.7b07460DOI Listing
September 2017

Exclusive Extracellular Bioreduction of Methyl Orange by Azo Reductase-Free Geobacter sulfurreducens.

Environ Sci Technol 2017 Aug 14;51(15):8616-8623. Epub 2017 Jul 14.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China , Hefei, 230026, China.

Azo dyes are a class of recalcitrant organic pollutants causing severe environmental pollution. For their biodecolorization, the azo reductase system was considered as the major molecular basis in bacteria. However, the intracellular localization of azo reductase limits their function for efficient azo dye decolorization. This limitation may be circumvented by electrochemically active bacteria (EAB) which is capable of extracellular respiration. To verify the essential role of extracellular respiration in azo dye decolorization, Geobacter sulfurreducens PCA, a model EAB, was used for the bioreduction of methyl orange (MO), a typical azo dye. G. sulfurreducens PCA efficiently reduced MO into amines. Kinetic results showed that G. sulfurreducens PCA had the highest decolorization efficiency among the currently known MO reducing bacteria. Electrons from acetate oxidization by this strain were transferred by the respiratory chain to MO. The mass and electron balances, fluorescent probing and proteinase K treatment experimental results indicate that the biodecolorization of MO by G. sulfurreducens PCA is an exclusive extracellular process. OmcB, OmcC and OmcE were identified as the key outer-membrane proteins for the extracellular MO reduction. This work deepens our understanding of EAB physiology and is useful for the decontamination of environments polluted with azo dyes. The contribution of extracellular respiration to pollutants reduction will broaden the environmental applications of EAB.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.est.7b02122DOI Listing
August 2017

Enhancing Extracellular Electron Transfer of Shewanella oneidensis MR-1 through Coupling Improved Flavin Synthesis and Metal-Reducing Conduit for Pollutant Degradation.

Environ Sci Technol 2017 May 21;51(9):5082-5089. Epub 2017 Apr 21.

CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China , Hefei, 230026, China.

Dissimilatory metal reducing bacteria (DMRB) are capable of extracellular electron transfer (EET) to insoluble metal oxides, which are used as external electron acceptors by DMRB for their anaerobic respiration. The EET process has important contribution to environmental remediation mineral cycling, and bioelectrochemical systems. However, the low EET efficiency remains to be one of the major bottlenecks for its practical applications for pollutant degradation. In this work, Shewanella oneidensis MR-1, a model DMRB, was used to examine the feasibility of enhancing the EET and its biodegradation capacity through genetic engineering. A flavin biosynthesis gene cluster ribD-ribC-ribBA-ribE and metal-reducing conduit biosynthesis gene cluster mtrC-mtrA-mtrB were coexpressed in S. oneidensis MR-1. Compared to the control strain, the engineered strain was found to exhibit an improved EET capacity in microbial fuel cells and potentiostat-controlled electrochemical cells, with an increase in maximum current density by approximate 110% and 87%, respectively. The electrochemical impedance spectroscopy (EIS) analysis showed that the current increase correlated with the lower interfacial charge-transfer resistance of the engineered strain. Meanwhile, a three times more rapid removal rate of methyl orange by the engineered strain confirmed the improvement of its EET and biodegradation ability. Our results demonstrate that coupling of improved synthesis of mediators and metal-reducing conduits could be an efficient strategy to enhance EET in S. oneidensis MR-1, which is essential to the applications of DMRB for environmental remediation, wastewater treatment, and bioenergy recovery from wastes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.est.6b04640DOI Listing
May 2017

Anaerobic reduction of 2,6-dinitrotoluene by Shewanella oneidensis MR-1: Roles of Mtr respiratory pathway and NfnB.

Biotechnol Bioeng 2017 04 21;114(4):761-768. Epub 2016 Nov 21.

CAS Key Laboratory of Urban Pollutant Conversion, University of Science and Technology of China, Hefei, 230026, China.

Dinitrotoluene (DNT) is a widely present pollutant in aquatic environments, and its biodegradation is an economically attractive way to effectively removal. In aquatic environments, the presence of electrochemically active bacteria (EAB) could contribute to the anaerobic bioreduction of DNT. However, the mechanism behind such a biodegradation process at gene level remains to be further elucidated. In this work, the anaerobic reduction of 2,6-dinitrotoluene (2,6-DNT) by Shewanella oneidensis MR-1, a typical EAB in aquatic environments, was investigated. S. oneidensis MR-1 was found to be able to obtain energy for growth through the anaerobic respiration on 2,6-DNT. Experimental results show that the Mtr respiratory pathway, a transmembrane electron transport chain, was involved in the 2,6-DNT bioreduction. Knockout of cymA or nfnB resulted in a substantial loss of its 2,6-DNT-reducing ability, indicating that both CymA and NfnB were the key proteins in the microbial electron transfer chain. The genetic analysis further confirms that the Mtr respiratory pathway and NfnB are mainly responsible for the anaerobic reduction of 2,6-DNT by S. oneidensis MR-1. This work is useful to better understand the anaerobic bioreduction of nitroaromatic compounds in aquatic environments and remediate the environments contaminated by nitroaromatic compounds. Biotechnol. Bioeng. 2017;114: 761-768. © 2016 Wiley Periodicals, Inc.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/bit.26212DOI Listing
April 2017

Interobserver variability in assessing dysplasia and architecture in colorectal adenomas: a multicentre Canadian study.

J Clin Pathol 2014 Sep;67(9):781-6

Aims: Following the introduction of colorectal cancer screening programmes throughout Canada, it became necessary to standardise the diagnosis of colorectal adenomas. Canadian guidelines for standardised reporting of adenomas were developed in 2011. The aims of the present study were (a) to assess interobserver variability in the classification of dysplasia and architecture in adenomas and (b) to determine if interobserver variability could be improved by the adoption of criteria specified in the national guidelines.

Methods: An a priori power analysis was used to determine an adequate number of cases and participants. Twelve pathologists independently classified 40 whole-slide images of adenomas according to architecture and dysplasia grade. Following a wash-out period, participants were provided with the national guidelines and asked to reclassify the study set.

Results: At baseline, there was moderate interobserver agreement for architecture (K=0.4700; 95% CI 0.4427 to 0.4972) and dysplasia grade (K=0.5680; 95% CI 0.5299 to 0.6062). Following distribution of the guidelines, there was improved interobserver agreement in assessing architecture (K=0.5403; 95% CI 0.5133 to 0.5674)). For dysplasia grade, overall interobserver agreement remained moderate but decreased significantly (K=0.4833; 95% CI 0.4452 to 0.5215). Half of the cases contained high-grade dysplasia (HGD). Two pathologists diagnosed HGD in ≥75% of cases.

Conclusions: The improvement in interobserver agreement in classifying adenoma architecture suggests that national guidelines can be useful in disseminating knowledge, however, the variability in the diagnosis of HGD, even following guideline review suggests the need for ongoing knowledge-transfer exercises.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1136/jclinpath-2014-202177DOI Listing
September 2014

Metabolic flux responses to genetic modification for shikimic acid production by Bacillus subtilis strains.

Microb Cell Fact 2014 Mar 14;13(1):40. Epub 2014 Mar 14.

State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China.

Background: Shikimic acid (SA) is a key chiral starting molecule for the synthesis of the neuramidase inhibitor GS4104 against viral influenza. Microbial production of SA has been extensively investigated in Escherichia coli, and to a less extent in Bacillus subtilis. However, metabolic flux of the high SA-producing strains has not been explored. In this study, we constructed with genetic manipulation and further determined metabolic flux with 13C-labeling test of high SA-producing B. subtilis strains.

Results: B. subtilis 1A474 had a mutation in SA kinase gene (aroI) and accumulated 1.5 g/L of SA. Overexpression of plasmid-encoded aroA, aroB, aroC or aroD in B. subtilis revealed that aroD had the most significantly positive effects on SA production. Simultaneous overexpression of genes for 3-deoxy-D-arabinoheptulosonate-7-phosphate synthase (aroA) and SA dehydrogenase (aroD) in B. subtilis BSSA/pSAAroA/pDGSAAroD resulted in SA production of 3.2 g/L. 13C-Metabolic flux assay (MFA) on the two strains BSSA/pHCMC04/pDG148-stu and BSSA/pSAAroA/pDGSAAroD indicated the carbon flux from glucose to SA increased to 4.6% in BSSA/pSAAroA/pDGSAAroD from 1.9% in strain BSSA/pHCMC04/pDG148-stu. The carbon flux through tricarboxylic acid cycle significantly reduced, while responses of the pentose phosphate pathway and the glycolysis to high SA production were rather weak, in the strain BSSA/pSAAroA/pDGSAAroD. Based on the results from MFA, two potential targets for further optimization of SA production were identified. Experiments on genetic deletion of phosphoenoylpyruvate kinase gene confirmed its positive influence on SA production, while the overexpression of the transketolase gene did not lead to increase in SA production.

Conclusion: Of the genes involved in shikimate pathway in B. subtilis, aroD exerted most significant influence on SA accumulation. Overexpression of plasmid-encoded aroA and aroD doubled SA production than its parent strain. MFA revealed metabolic flux redistribution among phosphate pentose pathway, glycolysis, TCA cycle in the low and high SA-producing B. subtilis strains. The high SA producing strain BSSA/pSAAroA/pDGSAAroD had increased carbon flux into shikimate pathway and reduced flux into TCA cycle.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/1475-2859-13-40DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4003833PMC
March 2014

Influence of heat stress on leaf ultrastructure, photosynthetic performance, and ascorbate peroxidase gene expression of two pear cultivars (Pyrus pyrifolia).

J Zhejiang Univ Sci B 2013 Dec;14(12):1070-83

State Agricultural Ministry Key Laboratory of Horticultural Plant Growth, Development and Quality Improvement, Department of Horticulture, Zhejiang University, Hangzhou 310058, China; College of Horticulture, Northwest A&F University, Yangling 712100, China.

Plants encounter a variety of stresses in natural environments. One-year-old pot-grown trees of pear (Pyrus pyrifolia Nakai cv. Cuiguan and Wonhwang) were exposed to two heat stress regimes. Under constant short-term heat stress, chloroplasts and mitochondria were visibly damaged. Relative chlorophyll content and maximum photochemical efficiency of photosystem II were significantly decreased, which indicated that the leaf photosynthetic capability declined. Under chronic heat stress, mesophyll cell ultrastructure was not obviously damaged, but leaf photosynthetic capability was still restrained. As chronic heat stress was a simulation of the natural environment in summer, further study of the responses under this stress regime was undertaken. Ascorbate peroxidase (APX) activity was increased in 'Cuiguan', but not in 'Wonhwang'. Inducible expression of PpAPX genes in the cytoplasm, chloroplasts and peroxisomes was consistent with increased APX activity in 'Cuiguan', whereas only weak induction of PpAPX genes was observed in 'Wonhwang'. The isoenzymes cytosolic APX1 (cAPX1) and stromal APX (sAPX) were confirmed to be localized in the cytoplasm and chloroplasts, respectively.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1631/jzus.B1300094DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3863366PMC
December 2013

Comparative study of terahertz radiation from n-InAs and n-GaAs.

Authors:
Dong-Feng Liu Du Xu

Appl Opt 2007 Feb;46(5):789-94

School of Information Engineering, Guangdong University of Technology, China.

We have studied terahertz (THz) emissions from n-InAs and n-GaAs using an ensemble Monte Carlo method. Our simulations indicate that higher amplitude THz waves from n-InAs, compared with those from n-GaAs, result from the difference in the radiation mechanisms between these two samples and are not completely dependent on the most commonly recognized fact: lighter electron effective mass in n-InAs. The excitation-wavelength-dependent and doping-level-dependent THz emissions from n-InAs are found to be quite different from those from n-GaAs. The corresponding mechanisms are analyzed by the introduction of a weighted electric field, which is weighted by the photogenerated carrier density in a semiconductor. The simulated results are in good qualitative agreement with experimental observations from other authors.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/ao.46.000789DOI Listing
February 2007
-->