Desulfovibrio Vulgaris Research Articles

Expression, Purification and Characterization of a ZIP Family Transporter from Desulfovibrio vulgaris.

The ZIP family transport zinc ions from the extracellular medium across the plasma membrane or from the intracellular compartments across endomembranes, which play fundamental roles in metal homeostasis and are broadly involved in physiological and pathological processes. Desulfovibrio is the predominant sulphate-reducing bacteria in human colonic microbiota, but also a potential choice for metal bioremediation. while, there are no published studies describing the zinc transporters from Desulfovibrio up to now. In this study, we obtained for the first time a heterologously expressed ZIP homolog from Desulfovibrio vulgaris, termed dvZip. The purified dvZip was reconstituted into proteoliposomes, and confirmed its zinc transport ability in vitro. By combining topology prediction, homology modeling and phylogenetic approaches, we also noticed that dvZip belongs to the GufA and probably have 8 transmembrane α-helical segments (TM 1-8) in which both termini are located on the extracellular, with TM2, 4, 5 and 7 create an inner bundle. We believe that purification and characterization of zinc (probably also cadmium) transporters from Desulfovibrio vulgaris such as dvZip could shed light on understanding of metal homeostasis of Desulfovibrio and provided protein products for future detailed function and structural studies.

MICROEVOLUTION OF DESULFOVIBRIO VULGARIS CO-CULTURED WITH METHANOSARCINA BARKERI REVEALED BY GENOME RE-SEQUENCING AND SINGLE-CELL RT-QPCR ANALYSIS

An integrative approach of adaptive laboratory evolution, whole-genome sequencing and single-cell analysis was used to explore mechanisms related to establishment and maintenance of syntrophic interaction between sulfate-reducing Desulfovibrio vulgaris and methanogen Methanosarcina barkeri. Adaptive laboratory evolution of the D. vulgaris and M. barkeri dual-cultures under two different concentrations of electron donor lactate (38 mM and 50 mM) was conducted by propagating continuously for 50 transfers (~200 generations). Physiological analysis showed that, compared with the initial dual-cultures, the adapted dual-cultures (E38 and E50) have increased growth rates (1.1-fold and 1.2 -fold) and higher biomass yields (3.0-fold and 3.8-fold) on 38 mM and 50 mM lactate, respectively. Whole-genome re-sequencing of D. vulgaris in the adapted dual-cultures revealed 11 and 12 mutations in the D. vulgaris genomes of E38 and E50 dual-cultures, respectively, among which 4 mutations were found in both adapted dual-cultures. RT-qPCR analysis showed that the expression levels of 8 mutated genes were gradually up-regulated in D. vulgaris along with the evolution process. In addition, their heterogeneity was found decreased along with the evolution, as revealed by single-cell RT-qPCR analysis, reflecting adjustments of both gene expression and gene heterogeneity to the gradually established syntrophic relationship.

Genetic Basis of Chromate Adaptation and the Role of the Pre-existing Genetic Divergence during an Experimental Evolution Study with Desulfovibrio vulgaris Populations.

ABSTRACTHexavalent chromium [Cr(VI)] is a common environmental pollutant. However, little is known about the genetic basis of microbial evolution under Cr(VI) stress and the influence of the prior evolution histories on the subsequent evolution under Cr(VI) stress. In this study, Desulfovibrio vulgaris Hildenborough (DvH), a model sulfate-reducing bacterium, was experimentally evolved for 600 generations. By evolving the replicate populations of three genetically diverse DvH clones, including ancestor (AN, without prior experimental evolution history), non-stress-evolved EC3-10, and salt stress-evolved ES9-11, the contributions of adaptation, chance, and pre-existing genetic divergence to the evolution under Cr(VI) stress were able to be dissected. Significantly decreased lag phases under Cr(VI) stress were observed in most evolved populations, while increased Cr(VI) reduction rates were primarily observed in populations evolved from EC3-10 and ES9-11. The pre-existing genetic divergence in the starting clones showed strong influences on the changes in lag phases, growth rates, and Cr(VI) reduction rates. Additionally, the genomic mutation spectra in populations evolved from different starting clones were significantly different. A total of 14 newly mutated genes obtained mutations in at least two evolved populations, suggesting their importance in Cr(VI) adaptation. An in-frame deletion mutation of one of these genes, the chromate transporter gene DVU0426, demonstrated that it played an important role in Cr(VI) tolerance. Overall, our study identified potential key functional genes for Cr(VI) tolerance and demonstrated the important role of pre-existing genetic divergence in evolution under Cr(VI) stress conditions.IMPORTANCE Chromium is one of the most common heavy metal pollutants of soil and groundwater. The potential of Desulfovibrio vulgaris Hildenborough in heavy metal bioremediation such as Cr(VI) reduction was reported previously; however, experimental evidence of key functional genes involved in Cr(VI) resistance are largely unknown. Given the genetic divergence of microbial populations in nature, knowledge on how this divergence affects the microbial adaptation to a new environment such as Cr(VI) stress is very limited. Taking advantage of our previous study, three groups of genetically diverse D. vulgaris Hildenborough populations with or without prior experimental evolution histories were propagated under Cr(VI) stress for 600 generations. Whole-population genome resequencing of the evolved populations revealed the genomic changes underlying the improved Cr(VI) tolerance. The strong influence of the pre-existing genetic divergence in the starting clones on evolution under Cr(VI) stress conditions was demonstrated at both phenotypic and genetic levels.

D-Tyrosine enhancement of microbiocide mitigation of carbon steel corrosion by a sulfate reducing bacterium biofilm.

Microbiocides are used to control problematic microorganisms. High doses of microbiocides cause environmental and operational problems. Therefore, using microbiocide enhancers to make microbiocides more efficacious is highly desirable. 2,2-dibromo-3-nitrilopropionamide (DBNPA) is a popular biodegradable microbiocide. D-Amino acids have been used in lab tests to enhance microbiocides to treat microbial biofilms. In this investigation, D-tyrosine was used to enhance DBNPA against Desulfovibrio vulgaris biofilm on C1018 carbon steel. After 7days of incubation, the mass loss of coupons without treatment chemicals in the ATCC 1249 culture medium was found to be 3.1 ± 0.1mg/cm2. With 150ppm (w/w) DBNPA in the culture medium, the mass loss was reduced to 1.9 ± 0.1mg/cm2 accompanied by a 1-log reduction in the sessile cell count. The 150ppm DBNPA + 1ppm D-tyrosine combination attained an extra 3-log reduction in sessile cell count and an additional 30% reduction in mass loss compared with 150ppm DBNPA only treatment. The combination also led to a smaller maximum pit depth. Linear polarization resistance (LPR), electrochemical impedance spectrometry (EIS), and potentiodynamic polarization (PDP) tests corroborated the enhancement effects.

Microbial corrosion of DSS 2205 in an acidic chloride environment under continuous flow.

Corrosion under flow conditions is a major problem in the transportation industry. Various studies have shown the direct impact of different flow rates on bacteria biofilm formation, mass transfer and resulting different corrosion behaviour of materials in neutral environments. However, little is understood on corrosion under acidic flow conditions. This study investigated the impact of an acidic artificial seawater environment containing Desulfovibrio vulgaris on DSS 2205 microbial corrosion under different velocities (0.25 m.s-1 and 0.61 m.s-1). Experiments containing no bacteria were performed as controls. Bacterial attachment was observed by optical and scanning electron microscope (SEM). Materials corrosion was assessed using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. Pits formed after potentiodynamic test were observed under SEM. The largest area of bacterial attachment was found on coupons immersed at a velocity of 0.25 m.s-1; however, the corrosion rate was lower than at higher velocity. Shallow pits occurred in the metal coupons when bacteria were present, while deep pits occurred in the controls. The study indicates the positive impact of biofilm formation in corrosion prevention of materials under acidic condition. The nature of corrosion behaviour of duplex stainless is discussed.

Deciphering the black box of microbial community of common effluent treatment plant through integrated metagenomics: Tackling industrial effluent

Identifying the microbial community and their functional potential from different stages of common effluent treatment plants (CETP) can enhance the efficiency of wastewater treatment systems. In this study, wastewater metagenomes from 8 stages of CETP were screened for microbial diversity and gene profiling along with their corresponding degradation activities. The microbial community displayed 98.46% of bacterial species, followed by Eukarya (0.10%) and Archaea 0.02%. At the Phylum level, Proteobacteria (28.8%) was dominant, followed by Bacteroidetes (16.1%), Firmicutes (11.7%), and Fusobacteria (6.9%) which are mainly capable of degrading the aromatic compounds. Klebsiella pneumoniae, Wolinella succinogenes, Pseudomonas stutzeri, Desulfovibrio vulgaris, and Clostridium sticklandii were the most prevalent species. The functional analysis further demonstrated the presence of enzymes linked with genes/pathways known to be involved in the degradation/metabolization of aromatic compounds like benzoate, bisphenol, 1,2-dichloroethane phenylalanine. This information was further validated with the whole genome analysis of the bacteria isolated from the CETP. We anticipate that integrating both shotgun and whole-genome analyses can reveal the rich reservoir for novel enzymes and genes present in CETP effluent that can contribute to designing efficient bioremediation strategies for the environment in general CETP system, in particular.

Insight the roles of loosely-bound and tightly-bound extracellular polymeric substances on Cu2+, Zn2+ and Pb2+ biosorption process with Desulfovibrio vulgaris

The aim of this study is to explore the fate and mechanism of metal cations of biosorption in the Desulfovibrio vulgaris system (including bacterial cells and secreted loosely-bound extracellular polymeric substances (LB-EPS) and tightly-bound extracellular polymeric substances (TB-EPS)). The relative contribution of EPS (TB-EPS and LB-EPS) to the adsorption of three metal cations is much greater than that of bacterial cells, and the adsorption capacity of Pb2+ on EPS (TB-EPS and LB-EPS) is much greater than that of Cu2+ and Zn2+ (Pb2+ > Cu2+ > Zn2+). The order of absorption capacity was as follows: LB-EPS > TB-EPS > bacterial cells, the adsorption contribution of EPS (including TB-EPS and LB-EPS) to Cu2+, Zn2+ and Pb2+ accounted for total adsorption capacity was 82%, 83% and 86%, respectively. It was suggested that LB-EPS was the first reaction barrier of immobilization metal cations before metal cations was able to pass through EPS and react with cells. The adsorption process was dominated by complexation and electrostatic interaction. The three-dimensional excitation-emission matrix (3D-EEM) identified two main fluorescence peaks of the aromatic and tryptophan protein-like substances in EPS. According to the synchronous fluorescence spectra, the tryptophan protein-like substances were gradually quenched with increased metal cations concentrations, which the quencher mechanism is dynamic quenching. The findings of this work are significant to reveal the fate of Cu2+, Zn2+ and Pb2+ during its sorption process onto Desulfovibrio vulgaris, and provide useful information of the interaction between Desulfovibrio vulgaris and its secreted EPS with metal cations.

The Challenge of Visualizing the Bridging Hydride at the Active Site and Proton Network of [NiFe]-Hydrogenase by Neutron Crystallography

X-ray crystallography is the most powerful tool for obtaining structural information about protein molecules, affording accurate and precise positions for all of the atoms in the protein except for hydrogen. However, hydrogen species play crucial roles in the physiological functions of enzymes, including molecular recognition through hydrogen bonding and catalytic reactions involving proton transfer. Neutron crystallography enables direct identification of the positions of hydrogen species. [NiFe]-hydrogenase from Desulfovibrio vulgaris Miyazaki F is an enzyme that catalyzes the reversible oxidation of molecular hydrogen. It contains a bimetallic Ni–Fe active site for the catalytic reaction and three Fe–S clusters for electron transfer. Previous X-ray structure analyses of the enzyme under various oxidation conditions have revealed that the active site changes its coordination structure depending on the redox state. In the inactive air-oxidized form, an oxygen species was identified between the Ni and Fe atoms, whereas in the active H2-reduced form, subatomic-resolution X-ray structure analysis and single-crystal EPR analyses indicated a hydride ligand between the two metal atoms. However, the assignment of the hydride moiety by X-ray crystallography remains controversial, and the proton transfer pathways in the molecule are still ambiguous. To allow neutron diffraction experiments, large crystals of [NiFe]-hydrogenase were prepared by the vapor diffusion method with the macroseeding technique according to the two-dimensional phase diagram (protein concentration vs. precipitant concentration). Neutron diffraction data were collected at approximately 2.0 A resolution at cryogenic temperature using a gas-stream cooling system to trap short-lived intermediates in the catalytic reaction.

Deletion Mutants, Archived Transposon Library, and Tagged Protein Constructs of the Model Sulfate-Reducing Bacterium Desulfovibrio vulgaris Hildenborough.

The dissimilatory sulfate-reducing deltaproteobacterium Desulfovibrio vulgaris Hildenborough (ATCC 29579) was chosen by the research collaboration ENIGMA to explore tools and protocols for bringing this anaerobe to model status. Here, we describe a collection of genetic constructs generated by ENIGMA that are available to the research community.

Mastication of polyolefins alters the microbial composition in Galleria mellonella.

Recent studies have indicated that Galleria mellonella larvae ingest polyethylene films and the degradation mechanism could inspire biotechnological exploitation for degrading plastic to eliminate global pollution from plastic waste. In this study, we tested the chemical compositions of masticated and ingested different plastic types by G.mellonella. High throughput sequencing of 16S rRNA gene was used to characterize the alteration of the microbial communities derived from salivary glands, gut contents and whole G.mellonella larvae. Our results indicated that G.mellonella is able to masticate polyethylene (PE), expanded polystyrene (EPS) and polypropylene (PP) and convert it to small particles with very large and chemically modified surfaces. The characteristics of the polymer affect the rate of damage. Formation of functional carbonyl groups on the appearance of oxidized metabolic intermediates of polyolefins in the frass samples observed. We found that the mastication of EPS, PP or PE could significantly alter the microbial composition in the gut content while it did not appear to influence the salivary glands microbial community. Representatives of Desulfovibrio vulgaris and Enterobacter grew with the PE diet while mastication of polystyrene and polypropylene increased the abundance of Enterococcus. The evaluation of bacterial communities in whole larvae confirmed the obtained result and additionally showed that the abundance of Paenibacillus, Corynebacterium and Commamonadaceae increased by Styrofoam (EPS) consumption.

Assessment of 2,2-Dibromo-3-Nitrilopropionamide Biocide Enhanced by D-Tyrosine against Zinc Corrosion by a Sulfate Reducing Bacterium

The biocorrosion of pure zinc by sulfate reducing bacterium (SRB) Desulfovibrio vulgaris was found to be very severe (2.3 ± 0.1 mm/y) after 7 d incubation in 100 mL of ATCC 1249 medium at 37 °C in ...

Bioelectrocatalytic Activity of W-Formate Dehydrogenase Covalently Immobilized on Functionalized Gold and Graphite Electrodes.

The decrease of greenhouse gases such as CO2 has become a key challenge for the human kind and the study of the electrocatalytic properties of CO2-reducing enzymes such as formate dehydrogenases is of importance for this goal. In this work, we study the covalent bonding of Desulfovibrio vulgaris Hildenborough FdhAB formate dehydrogenase to chemically modified gold and low-density graphite electrodes, using electrostatic interactions for favoring oriented immobilization of the enzyme. Electrochemical measurements show both bioelectrocatalytic oxidation of formate and reduction of CO2 by direct electron transfer (DET). Atomic force microscopy and quartz crystal microbalance characterization, as well as a comparison of direct and mediated electrocatalysis, suggest that a compact layer of formate dehydrogenase was anchored to the electrode surface with some crosslinked aggregates. Furthermore, the operational stability for CO2 electroreduction to formate by DET is shown with approximately 100% Faradaic yield.

OrpR is a σ54 -dependent activator using an iron-sulfur cluster for redox sensing in Desulfovibrio vulgaris Hildenborough.

Enhancer binding proteins (EBPs) are key players of σ54‐regulation that control transcription in response to environmental signals. In the anaerobic microorganism Desulfovibrio vulgaris Hildenborough (DvH), orp operons have been previously shown to be coregulated by σ54‐RNA polymerase, the integration host factor IHF and a cognate EBP, OrpR. In this study, ChIP‐seq experiments indicated that the OrpR regulon consists of only the two divergent orp operons. In vivo data revealed that (i) OrpR is absolutely required for orp operons transcription, (ii) under anaerobic conditions, OrpR binds on the two dedicated DNA binding sites and leads to high expression levels of the orp operons, (iii) increasing the redox potential of the medium leads to a drastic down‐regulation of the orp operons expression. Moreover, combining functional and biophysical studies on the anaerobically purified OrpR leads us to propose that OrpR senses redox potential variations via a redox‐sensitive [4Fe–4S]2+ cluster in the sensory PAS domain. Overall, the study herein presents the first characterization of a new Fe–S redox regulator belonging to the σ54‐dependent transcriptional regulator family probably advantageously selected by cells adapted to the anaerobic lifestyle to monitor redox stress conditions.

Synergistic epistasis enhances the co-operativity of mutualistic interspecies interactions

Early evolution of mutualism is characterized by big and predictable adaptive changes, including the specialization of interacting partners, such as through deleterious mutations in genes not required for metabolic cross-feeding. We sought to investigate whether these early mutations improve cooperativity by manifesting in synergistic epistasis between genomes of the mutually interacting species. Specifically, we have characterized evolutionary trajectories of syntrophic interactions of Desulfovibrio vulgaris (Dv) with Methanococcus maripaludis (Mm) by longitudinally monitoring mutations accumulated over 1000 generations of nine independently evolved communities with analysis of the genotypic structure of one community down to the single-cell level. We discovered extensive parallelism across communities despite considerable variance in their evolutionary trajectories and the perseverance within many evolution lines of a rare lineage of Dv that retained sulfate-respiration (SR+) capability, which is not required for metabolic cross-feeding. An in-depth investigation revealed that synergistic epistasis across pairings of Dv and Mm genotypes had enhanced cooperativity within SR− and SR+ assemblages, enabling their coexistence within the same community. Thus, our findings demonstrate that cooperativity of a mutualism can improve through synergistic epistasis between genomes of the interacting species, enabling the coexistence of mutualistic assemblages of generalists and their specialized variants.

Computational approaches to amino acid side-chain conformation using combined NMR theoretical and experimental results: leucine-67 in Desulfovibrio vulgaris flavodoxin.

In this paper, we show that the combination of NMR theoretical and experimental results can help to solve the molecular structure of peptides, here it is used as an example the residue Leucine-67 in Desulfovibrio vulgaris flavodoxin. We apply a computational protocol based on the leucine amino acid dipeptide, which, using calculated and experimental spin-spin coupling constants, allows us to obtain the conformation of the amino acid side chain. Calculated results show that the best agreement is obtained when three conformers around the lateral chain angle $\chi _1$ are considered or when the dynamic effect in the torsional angles is included. The population of each structure is estimated and analyzed according to the correlation between those two approaches. Independently of the approach, the estimated $\chi _1$ angle in solution is close to the staggered value of -60$^\circ $ and deviates significantly from the average x-ray angle of -90$^\circ $.

Lessons and Considerations for the Creation of Universal Primers Targeting Non-Conserved, Horizontally Mobile Genes.

Effective and accurate primer design is an increasingly important skill as the use of PCR-based diagnostics in clinical and environmental settings is on the rise. While universal primer sets have been successfully designed for highly conserved core genes such as 16S rRNA and characteristic genes such as dsrAB and dnaJ, primer sets for mobile, accessory genes such as multidrug resistance efflux pumps (MDREP) have not been explored. Here, we describe an approach to create universal primer sets for select MDREP genes chosen from five superfamilies (SMR, MFS, MATE, ABC and RND) identified in a model community of six members (Acetobacterium woodii, Bacillus subtilis, Desulfovibrio vulgaris, Geoalkalibacter subterraneus, Pseudomonas putida and Thauera aromatica). Using sequence alignments and in silico PCR analyses, a new approach for creating universal primers sets targeting mobile, non-conserved genes has been developed and compared to more traditional approaches used for highly conserved genes. A discussion of the potential shortfalls of the primer sets designed this way are described. The approach described here can be adapted to any unique gene set and aid in creating a wider, more robust library of primer sets to detect less conserved genes and improve the field of PCR-based screening research.IMPORTANCE Increasing use of molecular detection methods, specifically PCR and qPCR, requires utmost confidence in the results while minimizing false positives and negatives due to poor primer designs. Frequently, these detection methods are focused on conserved, core genes which limits their applications. These screening methods are being used in various industries for specific genetic targets or key organisms such as viral or infectious strains, or characteristic genes indicating the presence of key metabolic processes. The significance of this work is to improve primer design approaches to broaden the scope of detectable genes. The use of the techniques explored here will improve detection of non-conserved genes through unique primer design approaches. Additionally, the approaches here highlight additional, important information which can be gleaned during the in silico phase of primer design which will improve our gene annotations based on percent identities.

Environmental Impact of Sulfate-Reducing Bacteria, Their Role in Intestinal Bowel Diseases, and Possible Control by Bacteriophages

Sulfate-reducing bacteria (SRB) represent a group of prokaryotic microorganisms that are widely spread in the anoxic environment (seabed, riverbed and lakebed sediments, mud, intestinal tract of humans and animals, metal surfaces). SRB species also have an impact on processes occurring in the intestinal tract of humans and animals, including the connections between their presence and inflammatory bowel disease (IBD). Since these SRB can develop antimicrobial resistance toward the drugs, including antibiotics and antimicrobial agents, bacteriophages could represent an additional potential effective treatment. The main objectives of the review were as follows: (a) to review SRB (both from intestinal and environmental sources) regarding their role in intestinal diseases as well as their influence in environmental processes; and (b) to review, according to literature data, the influence of bacteriophages on SRB and their possible applications. Since SRB can have a significant adverse influence on industry as well as on humans and animals health, phage treatment of SRB can be seen as a possible effective method of SRB inhibition. However, there are relatively few studies concerning the influence of phages on SRB strains. Siphoviridae and Myoviridae families represent the main sulfide-producing bacteria phages. The most recent studies induced, by UV light, bacteriophages from Desulfovibrio vulgaris NCIMB 8303 and Desulfovibrio desulfuricans ATCC 13541. Notwithstanding costly and medically significant negative impacts of phages on SRB, they have been the subject of relatively few studies. The current search for alternatives to chemical biocides and antibiotics has led to the renewed interest in phages as antibacterial biocontrol and therapeutic agents, including their use against SRB. Hence, phages might represent a promising treatment against SRB in the future.

Effect of pH regulation by sulfate-reducing bacteria on corrosion behaviour of duplex stainless steel 2205 in acidic artificial seawater.

Sulfate-reducing bacteria (SRB) can regulate environmental pH because of their metabolism. Because local acidification results in pitting corrosion, the potential capacity of pH regulation by SRB would have important consequences for electrochemical aspects of the bio-corrosion process. This study focused on identifying the effect of pH on the corrosion of duplex stainless steel 2205 in a nutrient-rich artificial seawater medium containing SRB species, Desulfovibrio vulgaris. Duplex stainless steel samples were exposed to the medium for 13 days at 37°C at pH ranging from 4.0 to 7.4. The open-circuit potential value, sulfide level, pH and number of bacteria in the medium were recorded daily. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were used to study the properties of the biofilms at the end of the experiments and the corrosion behaviour of the material. Inductively coupled plasma mass spectrometry was used to measure the concentration of cations Fe, Ni, Mo, Mn, Cr in the experimental solution after 13 days. Scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDX) were used for surface analysis. The results showed the pH changed from acidic values set at the beginning of the experiment to approximately pH 7.5 after 5 days owing to bacterial metabolism. After 13 days, the highest iron concentration was in the solution that was initially at pH 4 accompanied by pitting on the stainless steel. Sulfur was present on all specimens but with more sulfur at pH 4 in the EDX spectra. EIS showed the film resistance of the specimen at pH 4 was much lower than at pH 7.4 which suggests the corrosion resistance of the stainless steel was better at higher pH. The results of this study suggest that the corrosion process for the first few days exposure at low pH was driven by pH in solution rather than by bacteria. The increasing pH during the course of the experiment slowed down the corrosion process of materials originally at low pH. The nature and mechanism of SRB attack on duplex stainless steel at different acidic environments are discussed.

A study of bacteria adhesion and microbial corrosion on different stainless steels in environment containing Desulfovibrio vulgaris.

Stainless steel is an important material used in many applications due to its mechanical strength and corrosion-resistant properties. The high corrosion resistance of stainless steel is provided by the passive film. Different stainless steels have different alloy elements and surface properties which could have a significant influence on bacterial attachment to the surface and thus might result in different microbial corrosion behaviours. In this study, the effect of adhesion of sulfate-reducing bacteria (SRB) on corrosion behaviour in artificial seawater on different stainless steels was investigated. Stainless steel materials used were SS 410, SS 420, SS 316 and DSS 2205 and pure chromium. The contact angle was measured to study the effect of surface properties of materials. Adhesion was measured by counting cells attached to the surface of materials. The corrosion behaviour of the materials was measured by electrochemical testing including measuring open circuit potential, electrochemical impedance spectroscopy and potentiodynamic behaviour. The long-term corrosion behaviour of each material was studied after six months of exposure by measuring weight loss and surface analysis with scanning electron microscope with energy-dispersive X-ray analysis. Hydrophobicity had a strong effect on bacterial attachment. Alloying elements e.g. nickel also had shown its ability to attract bacteria to adhere on the surface. However, the corrosion rate of different materials is determined not only by bacterial attachment but also by the stability of the passive film which is determined by the alloying elements, such as Mo and Cr. Chromium showed high resistance to corrosion, possibly due to toxicity on bacterial attachment. The nature of bacterial attachment and corrosion behaviour of the materials are discussed.

Anaerobic Transformation and Detoxification of Sulfamethoxazole by Sulfate-Reducing Enrichments and Desulfovibrio vulgaris

Sulfamethoxazole (SMX) is a veterinary antibiotic that is not efficiently removed from wastewater by routine treatment and therefore can be detected widely in the environment. Here, we investigated whether microbial anaerobic transformation can contribute to the removal of SMX in constructed systems. We enriched SMX-transforming mixed cultures from sediment of a constructed wetland and from digester sludge of a wastewater treatment plant. Transformation of SMX was observed in both sulfate-reducing and methanogenic cultures, whereas nitrate-reducing cultures showed no SMX transformation. In sulfate-reducing cultures, up to 90% of an initial SMX concentration of 100-250 μM was removed within 6 weeks of incubation, and the experiments demonstrated that the transformation was microbially catalyzed. The transformation products in sulfate-reducing cultures were identified as the reduced and isomerized forms of the isoxazole SMX moiety. The transformation products did not spontaneously reoxidize to SMX after oxygen exposure, and their antibacterial activity was significantly decreased compared to SMX. Population analyses in sequential transfers of the sulfate-reducing cultures revealed a community shift toward the genus Desulfovibrio. We therefore tested a deposited strain of Desulfovibrio vulgaris Hildenborough for its capacity to transform SMX and observed the same transformation products and similar transformation rates as in the enrichment cultures. Our work suggests that an initial anaerobic step in wastewater treatment can reduce the concentration of SMX in effluents and could contribute to decreased SMX concentrations in the environment.