Roles of Organohalide-Respiring Dehalococcoidia in Carbon Cycling

Abstract

The class Dehalococcoidia within the Chloroflexi phylum comprises the obligate organohalide-respiring genera Dehalococcoides, Dehalogenimonas, and “Candidatus Dehalobium.” Knowledge of the unique ecophysiology and biochemistry of Dehalococcoidia has been largely derived from studies with enrichment cultures and isolates from sites impacted with chlorinated pollutants; however, culture-independent surveys found Dehalococcoidia sequences in marine, freshwater, and terrestrial biomes considered to be pristine (i.e., not impacted with organohalogens of anthropogenic origin). The broad environmental distribution of Dehalococcoidia, as well as other organohalide-respiring bacteria, supports the concept of active halogen cycling and the natural formation of organohalogens in various ecosystems. Dechlorination reduces recalcitrance and renders organics susceptible to metabolic oxidation by diverse microbial taxa. During reductive dechlorination, hydrogenotrophic organohalide-respiring bacteria, in particular Dehalococcoidia, can consume hydrogen to low consumption threshold concentrations (<0.3 nM) and enable syntrophic oxidation processes. These functional attributes and the broad distribution imply that Dehalococcoidia play relevant roles in carbon cycling in anoxic ecosystems.

Prokaryotic, Fungal, and Unicellular Eukaryotic Core Communities Across Three Sympatric Marine Sponges From the Southwestern Atlantic Coast Are Dominated Largely by Deterministic Assemblage Processes

“…These compounds are well known in Aplysina species ( Lira et al, 2011 ) and provide protection against predation ( Loh and Pawlik, 2014 ). However, it was demonstrated that Dehalococcoidia might be able to deactivate the chemical defense systems by dehalogenating halogenated signaling molecules ( Yang et al, 2020 ). Therefore, these functions might be executed by the enriched lineages associated with A. fulva .…”

Novel Chloroflexi genomes from the deepest ocean reveal metabolic strategies for the adaptation to deep-sea habitats

“…3) and previous studies [26,27]. In addition, the degradation of recalcitrant OM by Chloro exi may produce semi-labile intermediates serving as substrates for other taxa in the microbial community [38], which might be one of the reasons for previous observations that Chloro exi lineages play important roles in interactive networks of microbial community in the sediment of the hadal trenches [27].…”

“…Currently, deep-sea Chloro exi have mainly been implied in reductive dehalogenation [9,36,37], a strictly anaerobic process which utilizes halogenated organic compounds as electron acceptor to oxidize hydrogen (or formate) [38]. In contrast, the hydrolytic and oxidative degradation of organohalides are aerobic processes [35].…”

Bacterial and Archaeal Diversity and Abundance in Shallow Subsurface Clay Sediments at Jianghan Plain, China

“…Elusimicrobia, another microbial population appearing in bottom samples A5 and A6 (Figure 4), might contribute to various substrates for methanogens by sugar fermentation to acetate, malate and butyrate, suggested by recent reconstructed Elusimicrobia genomes analysis from groundwater and other natural environments (Meheust et al, 2020). Beyond methanogenesis, these fermentation products could also to be used by the members in class Dehalococcoidia residing in bottom samples A5 and A6 ( Figure 4B) to respire the organohalide, a widespread recalcitrant pollutant in groundwater systems (Yang et al, 2020).…”