The nexus of syntrophy‐associated microbiota in anaerobic digestion revealed by long‐term enrichment and community survey

Abstract

Anaerobic digestion (AD) processes are known to effectively convert organic waste to CO2 and CH4 , but much of the microbial ecology remains unclear. Specifically, we have limited insights into symbiotic syntroph and methanogen ('syntrophy') acid degradation, although they are essential for preventing process deterioration. Also, we often observed many uncharacterized or uncultivated organisms, but poorly understood their role(s) in relation to syntrophy. To define syntrophy-associated populations, this study enriched methanogenic communities with propionate, butyrate, benzoate, acetate, formate and H2 from two different inocula over 3 years. 16S pyrotag analysis revealed core populations of known syntrophs (six clades) and methanogens (nine clades) associated with acid degradation, and evidence for substrate- and/or inoculum-dependent specificity in syntrophic partnerships. Based on comprehensive re-evaluation of publically available microbial community data for AD, the known syntrophs and methanogens identified were clearly representatives of the AD-associated syntrophs and methanogens. In addition, uncultivated clades related to Bacteroidetes, Firmicutes, Actinobacteria and Chloroflexi were ubiquitously found in AD and enrichments. These organisms may be universally involved in AD syntrophic degradation, but only represented <23% of the yet-to-be-cultivated organisms (89 of 390 clades). Thus, the contribution of these uncultured organisms in AD remains unclear and warrants further investigation.

Microbial dark matter ecogenomics reveals complex synergistic networks in a methanogenic bioreactor

“…Hydrogenedentes' (formerly NKB19): a lipolytic glycerol degrader Hydrogenedentes is often associated with methanogenic environments (Riviere et al, 2009;Narihiro et al, 2014), but its ecological role has remained enigmatic. While the genomic technology available for our previous study was insufficient for metagenomically capturing Hydrogenedentes, implementing modern sequencing platforms allowed construction of a Hydrogenedentes pangenome and transcriptome.…”

Effects of added enzymes on sorted, unsorted and sorted-out barley: A model study on realtime viscosity and process potentials using rapid visco analyser

“…Nevertheless, the cultivation of pure cultures to be used as bioaugmentation inocula has specific technical difficulties and is cost-expensive due to required sterile conditions and special growth media (De Roy et al, 2014). Contrary to pure cultures, ammonia acclimatized (enriched) cultures have lower requirements to sterility (Narihiro et al, 2015). Additionally, adaptation of the AD process to high ammonia loads is well established (Rajagopal et al, 2013;Tian et al, 2017).…”

Syntrophy in Anaerobic Digestion

“…In other words, recent studies are trying to circumvent the limitation and laboriosness of isolation work, in particular, the isolation of syntrophs, one of the most difficult and time-consuming tasks. The state-of-the-art technologies have now proven that community structure and functional networks can be envisaged to a certain extent (Nobu et al 2014b;Narihiro et al 2014) and deciphering the byzantine community network using such approaches will progress rapidly over the next decade. Nonetheless, the most important point is that one can never circumvent isolation in order to comprehensively characterize a microorganism and unveil its true entity.…”

“…Metagenomics, including functional genes using high-throughput sequencing, is now extensively underway (Lykidis et al 2011;Nelson et al 2011;Sundberg et al 2013;Werner et al 2011;Narihiro et al 2014;Nobu et al 2014b). This striking approach is now uncovering a wider variety of organisms and functions within AD than ever thought.…”