Indirect Evidence Link PCB Dehalogenation with Geobacteraceae in Anaerobic Sediment-Free Microcosms

Abstract

Although polychlorinated biphenyls (PCBs) production was brought to a halt 30 years ago, recalcitrance to degradation makes them a major environmental pollutant at a global scale. Previous studies confirmed that organohalide-respiring bacteria (OHRB) were capable of utilizing chlorinated congeners as electron acceptor. OHRB belonging to the Phyla Chloroflexi and Firmicutes are nowadays considered as the main PCB-dechlorinating organisms. In this study, we aimed at exploring the involvement of other taxa in PCB dechlorination using sediment-free microcosms (SFMs) and the Delor PCB mixture. High rates of congener dehalogenation (up to 96%) were attained in long-term incubations of up to 692 days. Bacterial communities were dominated by Chloroflexi, Proteobacteria, and Firmicutes, among strictly simplified community structures composed of 12 major phyla only. In a first batch of SFMs, Dehalococcoides mccartyi closely affiliated with strains CG4 and CBDB1 was considered as the main actor associated with congener dehalogenation. Addition of 2-bromoethanesulfonate (BES), a known inhibitor of methanogenic activity in a second batch of SFMs had an adverse effect on the abundance of Dehalococcoides sp. Only two sequences affiliated to this Genus could be detected in two (out of six) BES-treated SFMs, contributing to a mere 0.04% of the communities. BES-treated SFMs showed very different community structures, especially in the contributions of organisms involved in fermentation and syntrophic activities. Indirect evidence provided by both statistical and phylogenetic analysis validated the implication of a new cluster of actors, distantly affiliated with the Family Geobacteraceae (Phylum δ-Proteobacteria), in the dehalogenation of low chlorinated PCB congeners. Members of this Family are known already for their dehalogenation capacity of chlorinated solvents. As a result, the present study widens the knowledge for the phylogenetic reservoir of indigenous PCB dechlorinating taxa.

Microbial community changes in methanogenic granules during the transition from mesophilic to thermophilic conditions

“…Among these microbes, genus T78 is a candidatus genus because of its unique 16S rRNA gene sequences compared with other genera belonging to the same taxon. This genus was previously found in anaerobic digestion and biogas systems, possibly metabolizing alcohols and carbohydrates via syntrophic interactions (Praveckova et al 2016). Members from Genus T78 were taxonomically assigned to family Anaerolinaceae and predominated in the community throughout all three experiment periods.…”

Impact of hydraulic retention time and current on the microbial community and denitrification genes in a continuous‐flow biofilm electrode reactor

“…As the applied current was increased to 20 mA, Paracoccus , SHD‐231 , T78 , Longilinea , Steroidobacter and Azoarcus decreased in relative abundance, whereas Hyphomicrobium and Clostridium increased. Among these species, genus T78 was detected in an anaerobic digestion system, and could utilize alcohols and carbohydrates via syntrophic interactions . The decrease in T78 could be ascribed to the sharp decrease in the order Anaerolineales.…”

Characterization of the belowground microbial community in a poplar-assisted bioremediation strategy for restoring a multi-contaminated soil

“…The comparison of DNA and cDNA showed that in fact different bacterial genera or percentages of each taxonomic group were active in the soil studied, highlighting not only the role of Proteobacteria, but also some differences in the percentages of some classes between the bulk soil and rhizosphere. The Proteobacteria group includes most bacterial species involved in the main biogeochemical cycles and is typically the most abundant phylum found in a good quality state soil [34] and several Alpha-, Beta-, and Gammaproteobacteria species have been reported to be able to degrade PCBs and increase with a plant presence [13,35]. Interestingly, in cDNA a higher percentage of Firmicutes was also found and in this group there are several bacteria able to resist and remove HMs [36,37,38].…”