Interspecies interaction and effect of co-contaminants in an anaerobic dichloromethane-degrading culture.

An anaerobic stable mixed culture dominated by bacteria belonging to the genera Dehalobacterium, Acetobacterium, Desulfovibrio, and Wolinella was used as a model to study the microbial interactions during DCM degradation. Physiological studies indicated that DCM was degraded in this mixed culture at least in a three-step process: i) fermentation of DCM to acetate and formate, ii) formate oxidation to CO2 and H2, and iii) H2/CO2 reductive acetogenesis. The 16S rRNA gene sequencing of cultures enriched with formate or H2 showed that Desulfovibrio was the dominant population followed by Acetobacterium, but sequences representing Dehalobacterium were only present in cultures amended with DCM. Nuclear magnetic resonance analyses confirmed that acetate produced from 13C-labelled DCM was marked at the methyl ([2-13C]acetate), carboxyl ([1-13C]acetate), and both ([1,2-13C]acetate) positions, which is in accordance to acetate formed by both direct DCM fermentation and H2/CO2 acetogenesis. The inhibitory effect of ten different co-contaminants frequently detected in groundwaters on DCM degradation was also investigated. Complete inhibition of DCM degradation was observed when chloroform, perfluorooctanesulfonic acid, and diuron were added at 838, 400, and 107 μM, respectively. However, the inhibited cultures recovered the DCM degradation capability when transferred to fresh medium without co-contaminants. Findings derived from this work are of significant relevance to provide a better understanding of the synergistic interactions among bacteria to accomplish DCM degradation as well as to predict the effect of co-contaminants during anaerobic DCM bioremediation in groundwater.

Trueba-Santiso A ，Fernández-Verdejo D ，Marco-Rius I ，Soder-Walz JM ，Casabella O ，Vicent T ，Marco-Urrea E ... -  《-》

Mineralization versus fermentation: evidence for two distinct anaerobic bacterial degradation pathways for dichloromethane.

Chen G ，Fisch AR ，Gibson CM ，Erin Mack E ，Seger ES ，Campagna SR ，Löffler FE ... -  《-》

Mutualistic interaction between dichloromethane- and chloromethane-degrading bacteria in an anaerobic mixed culture.

The microbial mixed culture RM grows with dichloromethane (DCM) as the sole energy source generating acetate, methane, chloride and biomass as products. Chloromethane (CM) was not an intermediate during DCM utilization consistent with the observation that CM could not replace DCM as a growth substrate. Interestingly, cultures that received DCM and CM together degraded both compounds concomitantly. Transient hydrogen (H2 ) formation reaching a maximum concentration of 205 ± 13 ppmv was observed in cultures growing with DCM, and the addition of exogenous H2 at concentrations exceeding 3000 ppmv impeded DCM degradation. In contrast, CM degradation in culture RM had a strict requirement for H2 . Following five consecutive transfers on CM and H2 , Acetobacterium 16S rRNA gene sequences dominated the culture and the DCM-degrader Candidatus Dichloromethanomonas elyunquensis was eliminated, consistent with the observation that the culture lost the ability to degrade DCM. These findings demonstrate that culture RM harbours different populations responsible for anaerobic DCM and CM metabolism, and further imply that the DCM and CM degradation pathways are mechanistically distinct. H2 generated during DCM degradation is consumed by the hydrogenotrophic CM degrader, or may fuel other hydrogenotrophic processes, including organohalide respiration, methanogenesis and H2 /CO2 reductive acetogenesis.

Chen G ，Kleindienst S ，Griffiths DR ，Mack EE ，Seger ES ，Löffler FE ... -  《-》

Molecular and carbon isotopic characterization of an anaerobic stable enrichment culture containing Dehalobacterium sp. during dichloromethane fermentation.

Biodegradation of dichloromethane (DCM) under reducing conditions is of major concern due to its widespread detection in contaminated groundwaters. Here, we report an anaerobic enrichment culture derived from a membrane bioreactor operating in an industrial wastewater treatment plant, capable of fermenting DCM and the brominated analogue dibromomethane (DBM). Comparative analysis of bacterial 16S rDNA-DGGE profiles from fresh liquid medium inoculated with single colonies picked from serial dilution-to-extinction agar vials showed that cultures degrading DCM contained a predominant band belonging to Dehalobacterium, however this band was absent in cultures unable to degrade DCM. Analysis of the microbial composition of the enrichment by bacterial 16S rRNA gene amplicon paired-end sequencing confirmed the presence of Dehalobacterium together with three additional phylotypes belonging to Acetobacterium, Desulfovibrio, and Wolinella, representing all four operational taxonomic units >99.9% of the retrieved sequences. The carbon isotopic fractionation (ε) determined for DCM degradation in this culture was -27±2‰. This value differs from the ε previously reported for the DCM-fermentative bacteria Dehalobacter (-15.5±1.5‰) but they are both significantly different from those reported for facultative methylotrophic organisms (ranging from -45 to -61‰). This significant difference in the ε allows differentiating between hydrolytic transformation of DCM via glutathione-dependent dehalogenases and fermentation pathway. The carbon isotopic fractionation of dichloromethane by an enriched Dehalobacterium-containing culture has significant potential to monitor biodegradation of DCM in groundwaters.

Trueba-Santiso A ，Parladé E ，Rosell M ，Lliros M ，Mortan SH ，Martínez-Alonso M ，Gaju N ，Martín-González L ，Vicent T ，Marco-Urrea E ... -  《-》

Dichloromethane as the sole carbon source for an acetogenic mixed culture and isolation of a fermentative, dichloromethane-degrading bacterium.

Braus-Stromeyer SA ，Hermann R ，Cook AM ，Leisinger T ... -  《-》