Genome-centric metagenomic analysis revealed the microbial shifts in response to long-chain fatty acids (LCFA) in anaerobic digestion with hydrochar

Excessive long-chain fatty acids (LCFA) concentration inhibits the normal operation of anaerobic digestion (AD), while the influence of the concentration changes on the microbial communities in the AD has not been explored. In this study, three concentrations (0.25 gCOD/L, 0.5 gCOD/L, 1 gCOD/L) of oleate were investigated in AD to reveal the changes of microbial communities, and hydrochar (HC) was used as an additive to enhance the degradation of oleate in AD. The control groups were unable to maintain stable methanogenesis at all oleate concentrations after the second batch cultivation. However, the addition of HC effectively promoted the methanogenesis under all concentration conditions in the two consecutive batch cultivation. Microbial analysis of AD with HC showed that the relative abundances of Proteobacteria and Firmicutes were increased with increasing oleate concentration and the genus Azospira and genus Methanobacterium were the most abundant bacteria and archaea among the three groups, respectively. Genome-centric metagenomic analysis identified two previously unreported LCFA-degrading bacteria, namely Bin5 Azospira oryzae and Bin82 Pseudomonas balearica. Several microbes were significantly enriched at high oleate concentrations, which might be due to their possession of genes related to DNA repair, maintaining osmotic adjustment, pH homeostasis, and peptidoglycan and liposaccharide biosynthesis.