bDehalococcoides mccartyi 195 (strain 195) and Syntrophomonas wolfei were grown in a sustainable syntrophic coculture using butyrate as an electron donor and carbon source and trichloroethene (TCE) as an electron acceptor. The maximum dechlorination rate (9.9 ؎ 0.1 mol day ؊1 ) and cell yield [(1.1 ؎ 0.3) ؋ 10 8 cells mol ؊1 Cl ؊ ] of strain 195 maintained in coculture were, respectively, 2.6 and 1.6 times higher than those measured in the pure culture. The strain 195 cell concentration was about 16 times higher than that of S. wolfei in the coculture. Aqueous H 2 concentrations ranged from 24 to 180 nM during dechlorination and increased to 350 ؎ 20 nM when TCE was depleted, resulting in cessation of butyrate fermentation by S. wolfei with a theoretical Gibbs free energy of ؊13.7 ؎ 0.2 kJ mol ؊1 . Carbon monoxide in the coculture was around 0.06 mol per bottle, which was lower than that observed for strain 195 in isolation. The minimum H 2 threshold value for TCE dechlorination by strain 195 in the coculture was 0.6 ؎ 0.1 nM. Cell aggregates during syntrophic growth were observed by scanning electron microscopy. The interspecies distances to achieve H 2 fluxes required to support the measured dechlorination rates were predicted using Fick's law and demonstrated the need for aggregation. Filamentous appendages and extracellular polymeric substance (EPS)-like structures were present in the intercellular spaces. The transcriptome of strain 195 during exponential growth in the coculture indicated increased ATP-binding cassette transporter activities compared to the pure culture, while the membrane-bound energy metabolism related genes were expressed at stable levels. Groundwater contamination by trichloroethene (TCE), a potential human carcinogen, poses a serious threat to human health and can lead to the generation of vinyl chloride (VC), which is a known human carcinogen (1). Strains of Dehalococcoides mccartyi are the only known bacteria that can completely degrade TCE to the benign end product ethene. Biostimulation of indigenous Dehalococcoides spp. and bioaugmentation using Dehalococcoides-containing cultures are recognized as the most reliable in situ bioremediation technologies resulting in the complete dechlorination of TCE to ethene (2). However, the mechanisms that regulate the activity of D. mccartyi within natural ecosystems and shape its functional robustness in disturbed environments are poorly understood due to multiscale microbial community complexity and heterogeneity of biogeochemical processes involved in the sequential degradation (3, 4). D. mccartyi exhibits specific restrictive metabolic requirements for a variety of exogenous compounds, such as hydrogen, acetate, corrinoids, biotin, and thiamine, which can be supplied by other microbial genera through a complex metabolic network (1,(5)(6)(7)(8). Therefore, the growth of D. mccartyi is more robust within functionally diverse microbial communities that are deterministically assembled than in pure cultures (5,8,9). Previous studies have shown t...

In order to elucidate interactions between sulfate reduction and dechlorination, we systematically evaluated the effects of different concentrations of sulfate and sulfide on reductive dechlorination by isolates, constructed consortia, and enrichments containing Dehalococcoides sp. Sulfate (up to 5 mM) did not inhibit the growth or metabolism of pure cultures of the dechlorinator Dehalococcoides mccartyi 195, the sulfate reducer Desulfovibrio vulgaris Hildenborough, or the syntroph Syntrophomonas wolfei. In contrast, sulfide at 5 mM exhibited inhibitory effects on growth of the sulfate reducer and the syntroph, as well as on both dechlorination and growth rates of D. mccartyi. Transcriptomic analysis of D. mccartyi 195 revealed that genes encoding ATP synthase, biosynthesis, and Hym hydrogenase were downregulated during sulfide inhibition, whereas genes encoding metal-containing enzymes involved in energy metabolism were upregulated even though the activity of those enzymes (hydrogenases) was inhibited. When the electron acceptor (trichloroethene) was limiting and an electron donor (lactate) was provided in excess to cocultures and enrichments, high sulfate concentrations (5 mM) inhibited reductive dechlorination due to the toxicity of generated sulfide. The initial cell ratio of sulfate reducers to D. mccartyi (1:3, 1:1, or 3:1) did not affect the dechlorination performance in the presence of sulfate (2 and 5 mM). In contrast, under electron donor limitation, dechlorination was not affected by sulfate amendments due to low sulfide production, demonstrating that D. mccartyi can function effectively in anaerobic microbial communities containing moderate sulfate concentrations (5 mM), likely due to its ability to outcompete other hydrogen-consuming bacteria and archaea.IMPORTANCE Sulfate is common in subsurface environments and has been reported as a cocontaminant with chlorinated solvents at various concentrations. Inconsistent results for the effects of sulfate inhibition on the performance of dechlorination enrichment cultures have been reported in the literature. These inconsistent findings make it difficult to understand potential mechanisms of sulfate inhibition and complicate the interpretation of bioremediation field data. In order to elucidate interactions between sulfate reduction and reductive dechlorination, this study systematically evaluated the effects of different concentrations of sulfate and sulfide on reductive dechlorination by isolates, constructed consortia, and enrichments containing Dehalococcoides sp. This study provides a more fundamental understanding of the competition mechanisms between reductive dechlorination by Dehalococcoides mccartyi and sulfate reduction during the bioremediation process. It also provides insights on the significance of sulfate concentrations on reductive dechlorination under electron donor/acceptor-limiting conditions during in situ bioremediation applications. For example, at a trichloroethene-contaminated site with a high sulfate concentration, proper...

A halophilic bacterial consortium that degraded phenanthrene was developed from oil-contaminated saline soil containing 10% salinity. The biodegradation of phenanthrene occurred at 5%, 10%, and 15% salinity, whereas no biodegradation took place at 0.1% and 20% salinity. A 16S rRNA gene analysis showed that all sequences from the denaturing gradient gel electrophoresis profile were similar to those of halophilic bacteria. This is the first report of a halophilic bacterial consortium capable of degrading phenanthrene under hypersaline conditions.

A polycyclic aromatic hydrocarbon-degrading marine bacterium, designated strain P-4 T , was isolated from oil-polluted saline soil in Xianhe, Shangdong Province, China. Strain P-4 T was Gram-negative-staining with curved to spiral rod-shaped cells and grew optimally with 3-6 % (w/v) NaCl and at 30 6C. The predominant fatty acids were C 18 : 1 v7c (35.0 %), C 16 : 0 (25.0 %), C 16 : 1 v7c (17.9 %), C 14 : 0 (6.2 %) and C 17 : 0 cyclo (5.2 %). The major respiratory quinone was Q-9 and the genomic DNA G+C content was 61.2±1.0 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that strain P-4 T belonged to the genus Thalassospira of the class Alphaproteobacteria. DNA-DNA hybridization with Thalassospira xiamenensis DSM 17429 T showed relatedness of 36.0 %, and lower values were obtained with respect to other Thalassospira species. Based on physiological and biochemical tests and 16S rRNA gene sequence analysis as well as DNA-DNA relatedness, strain P-4 T should be placed in the genus Thalassospira within a novel species. The name Thalassospira xianhensis sp. nov. is proposed, with P-4 T (5CGMCC 1.6849 T 5JCM 14850 T ) as the type strain.Polycyclic aromatic hydrocarbons (PAHs) are hydrocarbons that consist of two or more fused aromatic rings (Habe & Omori, 2003;Hedlund & Staley, 2001). PAHs are released into the marine environment as a result of various anthropogenic activities such as marine seepage and accidental discharges during the transport and disposal of petroleum products and the use of fossil fuels (Sohn et al., 2004). Some PAHs are highly carcinogenic, genotoxic and cytotoxic to marine organisms and may be transferred to humans through seafood consumption (Menzie et al., 1992). Therefore, removal of PAHs from contaminated marine environments is of considerable importance.Several PAH-degrading strains have been isolated from PAH-contaminated marine sediments (Hedlund & Staley, 2001;Kwon et al., 2005;Sohn et al., 2004). In this study, we report the characterization of a PAH-degrading marine bacterium that was isolated from saline soil contaminated with crude oil in Xianhe, Shangdong Province, China.To isolate PAH-degrading bacteria, 5 % sea-salt defined medium (5 % SSDM; Zhao et al., 2009) and 5 % SSDM with 0.5 % yeast extract (5 % SSDMY) were used. Solid 5 % SSDMY medium was prepared with 1.5 % agar. A sample of oil-polluted saline soil (1 g) was added to 100 ml 5 % SSDM medium supplemented with phenanthrene (100 mg ml 21 ) in a 300 ml Erlenmeyer flask. The culture was aerobically incubated at 30 u C in darkness on a rotary shaker operating at 200 r.p.m. After 2 weeks, 10 ml culture was transferred to 100 ml 5 % SSDM medium and incubated under the conditions described above. The enrichment was performed five or six times. Next, a culture broth dilution series was spread on 5 % SSDMY agar. After incubation for 2 days, single colonies were picked and cultivated in 5 ml 5 % SSDM using phenanthrene as the sole source of carbon and energy. These isolates developed a yellowish-orange or red...