Long‐term investigation of microbial community composition and transcription patterns in a biogas plant undergoing ammonia crisis

Abstract

Summary Ammonia caused disturbance of biogas production is one of the most frequent incidents in regular operation of biogas reactors. This study provides a detailed insight into the microbial community of a mesophilic, full‐scale biogas reactor (477 kWh h −1 ) fed with maize silage, dried poultry manure and cow manure undergoing initial process disturbance by increased ammonia concentration. Over a time period of 587 days, the microbial community of the reactor was regularly monitored on a monthly basis by high‐throughput amplicon sequencing of the archaeal and bacterial 16S rRNA genes. During this sampling period, the total ammonia concentrations varied between 2.7 and 5.8 g l −1 [ NH 4 + –N]. To gain further inside into the active metabolic pathways, for selected time points metatranscriptomic shotgun analysis was performed allowing the quantification of marker genes for methanogenesis, hydrolysis and syntrophic interactions. The results obtained demonstrated a microbial community typical for a mesophilic biogas plant. However in response to the observed changing process conditions (e.g. increasing NH 4 + levels, changing feedstock composition), the microbial community reacted highly flexible by changing and adapting the community composition. The Methanosarcina ‐dominated archaeal community was shifted to a Methanomicrobiales‐dominated archaeal community in the presence of increased ammonia conditions. A similar trend as in the phylogenetic composition was observed in the transcription activity of genes coding for enzymes involved in acetoclastic methanogenesis and syntrophic acetate oxidations (Codh/Acs and Fthfs). In accordance, Clostridia simultaneously increased under elevated ammonia concentrations in abundance and were identified as the primary syntrophic interaction partner with the now Methanomicrobiales‐dominated archaeal community. In conclusion, overall stable process performance was maintained during increased ammonia concentration in the studied reactor based on the microbial communities’ ability to flexibly respond by reorganizing the community composition while remaining functionally stable.

Immediate Effects of Ammonia Shock on Transcription and Composition of a Biogas Reactor Microbiome

“…The starting material was obtained from a recently described reactor (Fischer et al, 2018). The volume of the commercial biogas fermenter was 2,800 m 3 , the organic load rate was 4.1 kg of organic dry matter per m 3 per day (3.7–4.5 within a year before and after sampling), and the hydraulic retention time was 76.1 days (varied between 69 and 93 days within a year before and after sampling).…”

“…Quality-trimmed sequences were analyzed using MOTHUR software, version 1.35.1 (Schloss et al, 2009). The analysis of the reads was performed as described recently (Fischer et al, 2018). Sequences were taxonomically classified using the Greengenes database (Version 13_05_99) (DeSantis et al, 2006).…”

“…Especially the methanogenic community appeared to be very sensitive toward changes in ammonia conditions. Among the methanogens, acetoclastic methanogenesis was observed to be inhibited already at lower ammonia levels whereas hydrogenotrophic methanogenesis was less sensitive toward increased ammonia concentrations (Sprott and Patel, 1986; Schnürer et al, 1994; Fotidis et al, 2014; Fischer et al, 2018).…”

“…Aiming to investigate the immediate response of the microbial community, its composition and gene expression in response to a rapid NH4+ upshift, we applied multiple analysis techniques in a replicated lab-scale simulation of a drastic increase in ammonium concentration from 4.9 to 8.0 g/L TAN using an inoculum from a previously described commercial biogas reactor. This reactor and its microbial community were already adapted to increased ammonium concentrations of 4.9 g/L TAN (Fischer et al, 2018). Methane production was used to monitor overall microbial metabolic productivity during the experiment.…”

Reduction in Hg phytoavailability in soil using Hg‐volatilizing bacteria and biochar and the response of the native bacterial community

“…Microbial community structure is critical for the maintenance of the health and stability of soil ecosystems because of the key role of various microorganisms in matter cycling and ecosystem service supply in soil (Wu et al ., ; Fischer et al ., ). Additionally, the microbial community can serve as a bioindicator of environmental variation (Castro et al ., ; Zhang et al ., ).…”