Phosphitispora fastidiosa gen. nov. sp. nov., a new dissimilatory phosphite-oxidizing anaerobic bacterium isolated from anaerobic sewage sludge.

A new strictly anaerobic bacterium, strain DYL19T, was enriched and isolated with phosphite as the sole electron donor and CO2 as a single carbon source and electron acceptor from anaerobic sewage sludge sampled at a sewage treatment plant in Constance, Germany. It is a Gram-positive, spore-forming, slightly curved, rod-shaped bacterium which oxidizes phosphite to phosphate while reducing CO2 to biomass and small amounts of acetate. Optimal growth is observed at 30 °C, pH 7.2, with a doubling time of 3 days. Beyond phosphite, no further inorganic or organic electron donor can be used, and no other electron acceptor than CO2 is reduced. Sulphate inhibits growth with phosphite and CO2. The G+C content is 45.95 mol%, and dimethylmenaquinone-7 is the only quinone detectable in the cells. On the basis of 16S rRNA gene sequence analysis and other chemotaxonomic properties, strain DYL19T is described as the type strain of a new genus and species, Phosphitispora fastidiosa gen. nov., sp. nov.

Desulfosporosinus metallidurans sp. nov., an acidophilic, metal-resistant sulfate-reducing bacterium from acid mine drainage.

A novel, spore-forming, acidophilic and metal-resistant sulfate-reducing bacterium, strain OLT, was isolated from a microbial mat in a tailing dam at a gold ore mining site. Cells were slightly curved immotile rods, 0.5 µm in diameter and 2.0-3.0 µm long. Cells were stained Gram-negative, despite the Gram-positive cell structure revealed by electron microscopy of ultrathin layers. OLT grew at pH 4.0-7.0 with an optimum at 5.5. OLT utilised H2, lactate, pyruvate, malate, formate, propionate, ethanol, glycerol, glucose, fructose, sucrose, peptone and tryptone as electron donors for sulfate reduction. Sulfate, sulfite, thiosulfate, nitrate and fumarate were used as electron acceptors in the presence of lactate. Elemental sulfur, iron (III), and arsenate did not serve as electron acceptors. The major cellular fatty acids were C16:1ω7c (39.0 %) and C16 : 0 (12.1 %). The draft genome of OLT was 5.29 Mb in size and contained 4909 protein-coding genes. The 16S rRNA gene sequence placed OLT within the phylum Firmicutes, class Clostridia, family Peptococcaceae, genus Desulfosporosinus. Desulfosporosinus nitroreducens 59.4BT was the closest relative with 97.6 % sequence similarity. On the basis of phenotypic and phylogenetic characteristics, strain OLT represents a novel species within the genus Desulfosporosinus, for which we propose the name Desulfosporosinus metallidurans sp. nov. with the type strain OLT (=DSM 104464T=VKM В-3021T).

Anaerobic Microbial Metabolism of Dichloroacetate.

Dichloroacetate (DCA) commonly occurs in the environment due to natural production and anthropogenic releases, but its fate under anoxic conditions is uncertain. Mixed culture RM comprising "Candidatus Dichloromethanomonas elyunquensis" strain RM utilizes DCA as an energy source, and the transient formation of formate, H2, and carbon monoxide (CO) was observed during growth. Only about half of the DCA was recovered as acetate, suggesting a fermentative catabolic route rather than a reductive dechlorination pathway. Sequencing of 16S rRNA gene amplicons and 16S rRNA gene-targeted quantitative real-time PCR (qPCR) implicated "Candidatus Dichloromethanomonas elyunquensis" strain RM in DCA degradation. An (S)-2-haloacid dehalogenase (HAD) encoded on the genome of strain RM was heterologously expressed, and the purified HAD demonstrated the cofactor-independent stoichiometric conversion of DCA to glyoxylate at a rate of 90 ± 4.6 nkat mg-1 protein. Differential protein expression analysis identified enzymes catalyzing the conversion of DCA to acetyl coenzyme A (acetyl-CoA) via glyoxylate as well as enzymes of the Wood-Ljungdahl pathway. Glyoxylate carboligase, which catalyzes the condensation of two molecules of glyoxylate to form tartronate semialdehyde, was highly abundant in DCA-grown cells. The physiological, biochemical, and proteogenomic data demonstrate the involvement of an HAD and the Wood-Ljungdahl pathway in the anaerobic fermentation of DCA, which has implications for DCA turnover in natural and engineered environments, as well as the metabolism of the cancer drug DCA by gut microbiota.IMPORTANCE Dichloroacetate (DCA) is ubiquitous in the environment due to natural formation via biological and abiotic chlorination processes and the turnover of chlorinated organic materials (e.g., humic substances). Additional sources include DCA usage as a chemical feedstock and cancer drug and its unintentional formation during drinking water disinfection by chlorination. Despite the ubiquitous presence of DCA, its fate under anoxic conditions has remained obscure. We discovered an anaerobic bacterium capable of metabolizing DCA, identified the enzyme responsible for DCA dehalogenation, and elucidated a novel DCA fermentation pathway. The findings have implications for the turnover of DCA and the carbon and electron flow in electron acceptor-depleted environments and the human gastrointestinal tract.

Sediment cooling triggers germination and sulfate reduction by heat-resistant thermophilic spore-forming bacteria.

Thermophilic endospores are widespread in cold marine sediments where the temperature is too low to support growth and activity of thermophiles in situ. These endospores are likely expelled from warm subsurface environments and subsequently dispersed by ocean currents. The endospore upper temperature limit for survival is 140°C, which can be tolerated in repeated short exposures, potentially enabling transit through hot crustal fluids. Longer-term thermal tolerance of endospores, and how long they could persist in an environment hotter than their maximum growth temperature, is less understood. To test whether thermophilic endospores can survive prolonged exposure to high temperatures, sediments were incubated at 80-90°C for 6, 12 or 463 days. Sediments were then cooled by 10-40°C, mimicking the cooling in subsurface oil reservoirs subjected to seawater injection. Cooling the sediments induced sulfate reduction, coinciding with an enrichment of endospore-forming Clostridia. Different Desulfofundulus, Desulfohalotomaculum, Desulfallas, Desulfotomaculum and Desulfofarcimen demonstrated different thermal tolerances, with some Desulfofundulus strains surviving for >1 year at 80°C. In an oil reservoir context, heat-resistant endospore-forming sulfate-reducing bacteria have a survival advantage if they are introduced to, or are resident in, an oil reservoir normally too hot for germination and growth, explaining observations of reservoir souring following cold seawater injection.

Domestication of previously uncultivated Candidatus Desulforudis audaxviator from a deep aquifer in Siberia sheds light on its physiology and evolution.

An enigmatic uncultured member of Firmicutes, Candidatus Desulforudis audaxviator (CDA), is known by its genome retrieved from the deep gold mine in South Africa, where it formed a single-species ecosystem fuelled by hydrogen from water radiolysis. It was believed that in situ conditions CDA relied on scarce energy supply and did not divide for hundreds to thousand years. We have isolated CDA strain BYF from a 2-km-deep aquifer in Western Siberia and obtained a laboratory culture growing with a doubling time of 28.5 h. BYF uses not only H2 but also various organic electron donors for sulfate respiration. Growth required elemental iron, and ferrous iron did not substitute for it. A complex intracellular organization included gas vesicles, internal membranes, and electron-dense structures enriched in phosphorus, iron, and calcium. Genome comparison of BYF with the South African CDA revealed minimal differences mostly related to mobile elements and prophage insertions. Two genomes harbored <800 single-nucleotide polymorphisms and had nearly identical CRISPR loci. We suggest that spores with the gas vesicles may facilitate global distribution of CDA followed by colonization of suitable subsurface environments. Alternatively, a slow evolution rate in the deep subsurface could result in high genetic similarity of CDA populations at two sites spatially separated for hundreds of millions of years.

Desulfofundulus australicus Wantanabe et al. 2018 is represented by a single deposit is one internationally operating collection.

The name Desulfofundulus australicusWantanabe et al. 2018 has appeared in the International Journal of Systematic and Evolutionary Microbiology and is based on the name Desulfotomaculum australicum Love et al. 1993. Consequently, both names are based on the nomenclatural type, strain AB33. At the time of valid publication of the name Desulfotomaculum australicum Love et al. 1993, the strain was also deposited in the Australian Collection of Microorganisms as ACM 3917 and was subsequently accessed to the DSMZ as DSM 11792. The publication of a new combination, Desulfofundulus australicusWantanabe et al. 2018, under Rule 27, and 30 (3b) of the International Code of Nomenclature of Prokaryotes requires that the nomenclatural type be deposited in at least two publicly accessible culture collections in different countries from which subcultures must be available in order that the new combination is validly published. The Australian Collection of Microorganisms no longer appears to operate and therefore the new combination, Desulfofundulus australicusWantanabe et al. 2018 is based on a single deposit in the DSMZ.

Co-occurrence network analysis reveals thermodynamics-driven microbial interactions in methanogenic bioreactors.

Methanogenic bioreactors have been applied to treat purified terephthalic acid (PTA) wastewater containing complex aromatic compounds, such as terephthalic acid, para-toluic acid and benzoic acid. This study characterized the interaction of microbial populations in 42 samples obtained from 10 PTA-degrading methanogenic bioreactors. Approximately, 54 dominant populations (11 methanogens, 8 syntrophs and 35 functionally unknown clades) that represented 73.9% of total 16S rRNA gene iTag sequence reads were identified. Co-occurrence analysis based on the abundance of dominant OTUs showed two non-overlapping networks centred around aromatic compound- (group AR: Syntrophorhabdaceae, Syntrophus and Pelotomaculum) and fatty acid- (group FA: Smithella and Syntrophobacter) degrading syntrophs. Group AR syntrophs have no direct correlation with hydrogenotrophic methanogens, while those from group FA do. As degradation of aromatic compounds has a wider thermodynamic window than fatty acids, Group AR syntrophs may be less influenced by fluctuations in hydrogenotrophic methanogen abundance or may non-specifically interact with diverse methanogens. In both groups, network analysis reveals full-scale- and lab-scale-specific uncultivated taxa that may mediate interactions between syntrophs and methanogens, suggesting that those uncultivated taxa may support the degradation of aromatic compounds through uncharted ecophysiological traits. These observations suggest that organisms from multiple niches orchestrate their metabolic capacity in multiple interaction networks to effectively degrade PTA wastewater.

Marinisporobacter balticus gen. nov., sp. nov., Desulfosporosinus nitroreducens sp. nov. and Desulfosporosinus fructosivorans sp. nov., new spore-forming bacteria isolated from subsurface sediments of the Baltic Sea.

Four novel Gram-stain-positive, endospore-forming bacteria of the order Clostridiales were isolated from subsurface sediments sampled during International Ocean Discovery Program Expedition 347 to the Baltic Sea. One strain (59.4MT) grew as an obligate heterotroph by aerobic respiration and anaerobically by fermentation. Optimum growth was observed with 0.5 % NaCl at 25 °C and pH 7.0-7.3. Analysis of 16S rRNA gene sequences of 59.4MT revealed Alkaliphilus transvaalensis (92.3 % identity), Candidatus Geosporobacter ferrireducens (92.2 %), Geosporobacter subterraneus (91.9 %) and Alkaliphilus peptidifermentans (91.7 %) to be the closest relatives. On the basis of the results of phenotypic and genotypic analyses, we propose that strain 59.4MT represents a novel species within a novel genus, Marinisporobacter balticus gen. nov., sp. nov., with the type strain 59.4MT (=DSM 102940T=JCM 31103T). Three other strains, 59.4F, 59.4BT and 63.6FT, were affiliated with the genus Desulfosporosinus and grew as strictly anaerobic sulfate reducers. These strains additionally used thiosulfate, elemental sulfur, sulfite and DMSO as electron acceptors and hydrogen as an electron donor. Strains 59.4F and 59.4BT had identical 16S rRNA gene sequences, which were most similar to those of Desulfosporosinus lacus (97.8 %), Desulfosporosinus hippei (97.3 %) and Desulfosporosinus orientis (97.3 %). Strain 63.6FT was closely related to D. lacus (97.7 %), Desulfosporosinus meridiei (96.6 %) and D. hippei (96.5 %). The similarity of 16S rRNA gene sequences of strains 59.4BT and 63.6FT was 96.6 %. We propose the new names Desulfosporosinus nitroreducens sp. nov., incorporating strain 59.4F (=DSM 101562=JCM 31104) and the type strain 59.4BT (=DSM 101608T=JCM 31105T), and Desulfosporosinus fructosivorans sp. nov., with the type strain 63.6FT (=DSM 101609T=JCM 31106T).

'Candidatus Dichloromethanomonas elyunquensis' gen. nov., sp. nov., a dichloromethane-degrading anaerobe of the Peptococcaceae family.

Taxonomic assignments of anaerobic dichloromethane (DCM)-degrading bacteria remain poorly constrained but are important for understanding the microbial diversity of organisms contributing to DCM turnover in environmental systems. We describe the taxonomic classification of a novel DCM degrader in consortium RM obtained from pristine Rio Mameyes sediment. Phylogenetic analysis of full-length 16S rRNA gene sequences demonstrated that the DCM degrader was most closely related to members of the genera Dehalobacter and Syntrophobotulus, but sequence similarities did not exceed 94% and 93%, respectively. Genome-aggregate average amino acid identities against Peptococcaceae members did not exceed 66%, suggesting that the DCM degrader does not affiliate with any described genus. Phylogenetic analysis of conserved single-copy functional genes supported that the DCM degrader represents a novel clade. Growth strictly depended on the presence of DCM, which was consumed at a rate of 160±3µmolL-1 d-1. The DCM degrader attained 5.25×107±1.0×107 cells per µmol DCM consumed. Fluorescence in situ hybridization revealed rod-shaped cells 4±0.8µm long and 0.4±0.1µm wide. Based on the unique phylogenetic, genomic, and physiological characteristics, we propose that the DCM degrader represents a new genus and species, 'Candidatus Dichloromethanomonas elyunquensis'.

Benzene degradation in a denitrifying biofilm reactor: activity and microbial community composition.

Benzene is an aromatic compound and harmful for the environment. Biodegradation of benzene can reduce the toxicological risk after accidental or controlled release of this chemical in the environment. In this study, we further characterized an anaerobic continuous biofilm culture grown for more than 14 years on benzene with nitrate as electron acceptor. We determined steady state degradation rates, microbial community composition dynamics in the biofilm, and the initial anaerobic benzene degradation reactions. Benzene was degraded at a rate of 0.15 µmol/mg protein/day and a first-order rate constant of 3.04/day which was fourfold higher than rates reported previously. Bacteria belonging to the Peptococcaceae were found to play an important role in this anaerobic benzene-degrading biofilm culture, but also members of the Anaerolineaceae were predicted to be involved in benzene degradation or benzene metabolite degradation based on Illumina MiSeq analysis of 16S ribosomal RNA genes. Biomass retention in the reactor using a filtration finger resulted in reduction of benzene degradation capacity. Detection of the benzene carboxylase encoding gene, abcA, and benzoic acid in the culture vessel indicated that benzene degradation proceeds through an initial carboxylation step.

Refined experimental annotation reveals conserved corrinoid autotrophy in chloroform-respiring Dehalobacter isolates.

Two novel chlorinated alkane-respiring Dehalobacter restrictus strains CF and DCA were isolated from the same enrichment culture, ACT-3, and characterized. The closed genomes of these highly similar sister strains were previously assembled from metagenomic sequence data and annotated. The isolation of the strains enabled experimental verification of predicted annotations, particularly focusing on irregularities or predicted gaps in central metabolic pathways and cofactor biosynthesis. Similar to D. restrictus strain PER-K23, strains CF and DCA require arginine, histidine and threonine for growth, although the corresponding biosynthesis pathways are predicted to be functional. Using strain CF to experimentally verify annotations, we determined that the predicted defective serine biosynthesis pathway can be rescued with a promiscuous serine hydroxymethyltransferase. Strain CF grew without added thiamine although the thiamine biosynthesis pathway is predicted to be absent; intracellular thiamine diphosphate, the cofactor of carboxylases in central metabolism, was not detected in cell extracts. Thus, strain CF may use amino acids to replenish central metabolites, portending entangled metabolite exchanges in ACT-3. Consistent with annotation, strain CF possesses a functional corrinoid biosynthesis pathway, demonstrated by increasing corrinoid content during growth and guided cobalamin biosynthesis in corrinoid-free medium. Chloroform toxicity to corrinoid-producing methanogens and acetogens may drive the conservation of corrinoid autotrophy in Dehalobacter strains. Heme detection in strain CF cell extracts suggests the 'archaeal' heme biosynthesis pathway also functions in anaerobic Firmicutes. This study reinforces the importance of incorporating enzyme promiscuity and cofactor availability in genome-scale functional predictions and identifies essential nutrient interdependencies in anaerobic dechlorinating microbial communities.

Desulfonatronospira sulfatiphila sp. nov., and Desulfitispora elongata sp. nov., two novel haloalkaliphilic sulfidogenic bacteria from soda lakes.

Two novel haloalkaliphilic bacteria with dissimilatory sulfidogenic metabolism were recovered from syntrophic associations obtained from anaerobic sediments of hypersaline soda lakes in Kulunda Steppe (Altai, Russia). Strain ASO3-2T was a member of a sulfidogenic syntrophic association oxidizing acetate at extremely haloalkaline conditions, and was isolated in pure culture using formate as electron donor and sulfate as electron acceptor. It was identified as representing a novel member of the genus Desulfonatronospira within the Deltaproteobacteria. In contrast to the two known species of this genus, the novel isolate was able to grow with formate as electron donor and sulfate, as well as with sulfite, as electron acceptor. Strain Acr1T was a minor component in a soda lake syntrophic association converting benzoate to methane and acetate. It became dominant in a subculture fed with crotonate. While growing on crotonate, strain Acr1T formed unusually long cells filled with polyhydroxyalkanoate-like granules. Its metabolism was limited to fermentation of crotonate and pyruvate and the ability to utilize thiosulfate and sulfur/polysulfide as electron acceptor. Strain Acr1T was identified as representing a novel member of the genus Desulfitispora in the class Clostridia. Both isolates were obligately haloalkaliphilic with extreme salt tolerance. On the basis of phenotypic and phylogenetic analyses, the novel sulfidogenic isolates from soda lakes are proposed to represent two novel species: Desulfonatronospira sulfatiphila sp. nov. (ASO3-2T=DSM 100427=UNIQEM U993T) and Desulfitispora elongata sp. nov. (Acr1T=DSM 29990=UNIQEM U994T).

Involvement of Dehalobacter strains in the anaerobic dechlorination of 2,4,6-trichlorophenol.

A culture reductively dechlorinating 2,4,6-trichlorophenol (TCP) was enriched from a sediment contaminated with chlorinated aliphatic hydrocarbons. The culture dechlorinated 100 µM of 2,4,6-TCP to 4-chlorophenol within 15 days utilizing H2 and a yeast extract as an electron donor and carbon source, respectively. Besides 2,4,6-TCP, the culture could also dehalogenate chlorophenols at ortho position and 2,4,6-tribromophenol at ortho and para positions, as well as chlorinated ethenes and ethanes. A 16S rRNA gene clone library analysis showed that the bacterial community was composed of members of the classes Clostridia, Bacteroidia, Spirochetes, and Epsilonproteobacteria. The phylogenetic and physiological characterization of the culture confirmed two novel Dehalobacter strains, TCP-5 and TCP-6, that were involved in the reductive dehalogenation of 2,4,6-TCP and other halogenated compounds. The study was significant as the first report to demonstrate the involvement of Dehalobacter in the reductive dehalogenation of both halogenated aromatic and aliphatic compounds.

Identification of Dehalobacter reductive dehalogenases that catalyse dechlorination of chloroform, 1,1,1-trichloroethane and 1,1-dichloroethane.

Two novel reductive dehalogenases (RDases) that are highly similar to each other but catalyse distinct dechlorination reactions were identified from Dehalobacter-containing mixed cultures. These two RDases were partially purified from crude protein extracts of anaerobic dechlorinating enrichment cultures using blue native polyacrylamide gel electrophoresis. Gel slices were assayed for dechlorinating activity, and associated proteins were identified using liquid chromatography tandem mass spectrometry with the metagenome of the parent culture as the reference database. The two RDases identified, annotated as CfrA and DcrA, share an amino acid identity of 95.2 per cent, but use different substrates: CfrA dechlorinates chloroform (CF) and 1,1,1-trichloroethane (1,1,1-TCA), but not 1,1-dichloroethane; DcrA dechlorinates 1,1-dichloroethane, but not CF or 1,1,1-TCA. These two novel RDases share no more than 40 per cent amino acid identity to any other known or putative RDases, but both have a twin-arginine motif and two iron-sulfur binding motifs conserved in most RDases. Peptides specific to two putative membrane anchor proteins, annotated as CfrB and DcrB, were also detected in gel slices.

Desulfosporosinus burensis sp. nov., a spore-forming, mesophilic, sulfate-reducing bacterium isolated from a deep clay environment.

A novel anaerobic, gram-positive, spore-forming, curved rod-shaped, mesophilic and sulfate-reducing bacterium was isolated from pore water collected in a borehole at -490 m in Bure (France). This strain, designated BSREI1(T), grew at temperatures between 5 °C and 30 °C (optimum 25 °C) and at a pH between 6 and 8 (optimum 7). It did not require NaCl for growth, but tolerated it up to 1.5 % NaCl. Sulfate, thiosulfate and elemental sulfur were used as terminal electron acceptors. Strain BSREI1(T) used crotonate, formate, lactate, pyruvate, fructose, glycerol and yeast extract as electron donors in the presence of sulfate. The sole quinone was MK-7. The G+C content of the genomic DNA was 43.3 mol%. Strain BSREI1(T) had the type strains of Desulfosporosinus lacus (16S rRNA gene sequence similarity of 96.83 %), Desulfosporosinus meridiei (96.31 %) and Desulfosporosinus hippei (96.16 %) as its closest phylogenetic relatives. On the basis of phylogenetic and physiological properties, strain BSREI1(T) is proposed as a representative of a novel species of the genus Desulfosporosinus, Desulfosporosinus burensis sp. nov.; the type strain is BSREI1(T) ( = DSM 24089(T) = JCM 17380(T)).

Community and proteomic analysis of methanogenic consortia degrading terephthalate.

Degradation of terephthalate (TA) through microbial syntrophy under moderately thermophilic (46 to 50°C) methanogenic conditions was characterized by using a metagenomic approach (A. Lykidis et al., ISME J. 5:122-130, 2011). To further study the activities of key microorganisms responsible for the TA degradation, community analysis and shotgun proteomics were used. The results of hierarchical oligonucleotide primer extension analysis of PCR-amplified 16S rRNA genes indicated that Pelotomaculum, Methanosaeta, and Methanolinea were predominant in the TA-degrading biofilms. Metaproteomic analysis identified a total of 482 proteins and revealed a distinctive distribution pattern of microbial functions expressed in situ. The results confirmed that TA was degraded by Pelotomaculum spp. via the proposed decarboxylation and benzoyl-coenzyme A-dependent pathway. The intermediate by-products, including acetate, H(2)/CO(2), and butyrate, were produced to support the growth of methanogens, as well as other microbial populations that could further degrade butyrate. Proteins related to energy production and conservation, and signal transduction mechanisms (that is, chemotaxis, PAS/GGDEF regulators, and stress proteins) were highly expressed, and these mechanisms were important for growth in energy-limited syntrophic ecosystems.

Complete genome sequences of Desulfosporosinus orientis DSM765T, Desulfosporosinus youngiae DSM17734T, Desulfosporosinus meridiei DSM13257T, and Desulfosporosinus acidiphilus DSM22704T.

Desulfosporosinus species are sulfate-reducing bacteria belonging to the Firmicutes. Their genomes will give insights into the genetic repertoire and evolution of sulfate reducers typically thriving in terrestrial environments and able to degrade toluene (Desulfosporosinus youngiae), to reduce Fe(III) (Desulfosporosinus meridiei, Desulfosporosinus orientis), and to grow under acidic conditions (Desulfosporosinus acidiphilus).

Dichloromethane fermentation by a Dehalobacter sp. in an enrichment culture derived from pristine river sediment.

Dichloromethane (DCM) as the sole substrate supported growth of a Dehalobacter sp. in an enrichment culture derived from noncontaminated river sediment. DCM was not reductively dechlorinated, and acetate was produced, indicating DCM fermentation and further suggesting Dehalobacter growth is not limited to organohalide respiration.

Arsenic precipitation by an anaerobic arsenic-respiring bacterial strain isolated from the polluted sediments of Orbetello Lagoon, Italy.

AIMS: To isolate and characterize an anaerobic bacterial strain from the deeper polluted lagoon sediment able to use as electron acceptors [As(V)] and sulfate (SO4(2-)), using lactate as an electron donor. METHODS AND RESULTS: Methods for isolation from polluted lagoon sediments included anaerobic enrichment cultures in the presence of As(V) and SO4(2-). Reduction of As(V) to As(III) was observed during the growth of the bacterial strain, and the final concentration of As(III) was lower than the initial As(V) one, suggesting the immobilization of As(III) in the yellow precipitate. The precipitate was identified by energy dispersive spectroscopy X-ray as arsenic sulfide. Scanning electron microscopy (SEM) revealed rod-shaped bacterial cells embedded in the precipitate, where net-like formations strictly related to the bacterial cells were visible. The surface of the precipitate showed the adhesion of bacterial cells, forming clusters. Transmission electron microscopy (TEM) also highlighted precipitates inside the bacterial cells and on their surface. Following 16S rRNA sequencing, the bacterial strain 063 was assigned to the genus Desulfosporosinus. CONCLUSIONS: This study reports, for the first time, the isolation from the polluted lagoon sediments of a strain capable of respiring and using As(V) and SO4(2-) as electron acceptors with lactate as the sole carbon and energy source with the formation of an arsenic sulfide precipitate. SIGNIFICANCE AND IMPACT OF THE STUDY: The identification of these properties provides novel insight into the possible use of the anaerobic strain in bioremediation processes and also adds to the knowledge on the biogeochemical cycling of arsenic.

A 'rare biosphere' microorganism contributes to sulfate reduction in a peatland.

Methane emission from peatlands contributes substantially to global warming but is significantly reduced by sulfate reduction, which is fuelled by globally increasing aerial sulfur pollution. However, the biology behind sulfate reduction in terrestrial ecosystems is not well understood and the key players for this process as well as their abundance remained unidentified. Comparative 16S rRNA gene stable isotope probing (SIP) in the presence and absence of sulfate indicated that a Desulfosporosinus species, which constitutes only 0.006% of the total microbial community 16S rRNA genes, is an important sulfate reducer in a long-term experimental peatland field site. Parallel SIP using dsrAB (encoding subunit A and B of the dissimilatory (bi)sulfite reductase) identified no additional sulfate reducers under the conditions tested. For the identified Desulfosporosinus species a high cell-specific sulfate reduction rate of up to 341 fmol SO4²â» cell⁻¹ day⁻¹ was estimated. Thus, the small Desulfosporosinus population has the potential to reduce sulfate in situ at a rate of 4.0-36.8 nmol (g soil w. wt.)⁻¹ day⁻¹, sufficient to account for a considerable part of sulfate reduction in the peat soil. Modeling of sulfate diffusion to such highly active cells identified no limitation in sulfate supply even at bulk concentrations as low as 10 µM. Collectively, these data show that the identified Desulfosporosinus species, despite being a member of the 'rare biosphere', contributes to an important biogeochemical process that diverts the carbon flow in peatlands from methane to CO2 and, thus, alters their contribution to global warming.