Bioreactor microbial ecosystems with differentiated methanogenic phenol biodegradation and competitive metabolic pathways unraveled with genome-resolved metagenomics

Feng Ju, Yubo Wang, Tong Zhang

Methanogenic biodegradation of aromatic compounds depends on syntrophic metabolism. However, metabolic enzymes and pathways of uncultured microorganisms and their ecological interactions with methanogenic consortia are unknown because of their resistance to isolation and limited genomic information. Genome-resolved metagenomics approaches were used to reconstruct and dissect 23 prokaryotic genomes from 37 and 20 °C methanogenic phenol-degrading reactors. Comparative genomic evidence suggests that temperature difference leads to the colonization of two distinct cooperative sub-communities that can respire sulfate/sulfite/sulfur or nitrate/nitrite compounds and compete for uptake of methanogenic substrates (e.g., acetate and hydrogen). This competition may differentiate methanogenesis. The uncultured ε-Proteobacterium G1, whose close relatives have broad ecological niches including the deep-sea vents, aquifers, sediment, limestone caves, spring, and anaerobic digesters, is implicated as a Sulfurovum-like facultative anaerobic diazotroph with metabolic versatility and remarkable environmental adaptability. We provide first genomic evidence for butyrate, alcohol, and carbohydrate utilization by a Chloroflexi T78 clade bacterium, and phenol carboxylation and assimilatory sulfite reduction in a Cryptanaerobacter bacterium. Genome-resolved metagenomics enriches our view on the differentiation of microbial community composition, metabolic pathways, and ecological interactions in temperature-differentiated methanogenic phenol-degrading bioreactors. These findings suggest optimization strategies for methanogenesis on phenol, such as temperature control, protection from light, feed desulfurization, and hydrogen sulfide removal from bioreactors. Moreover, decoding genome-borne properties (e.g., antibiotic, arsenic, and heavy metal resistance) of uncultured bacteria help to bring up alternative schemes to isolate them.