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

Abstract

The biotechnological process of biogas production from organic material is carried out by a diverse microbial community under anaerobic conditions. However, the complex and sensitive microbial network present in anaerobic degradation of organic material can be disturbed by increased ammonia concentration introduced into the system by protein-rich substrates and imbalanced feeding. Here, we report on a simulated increase of ammonia concentration in a fed batch lab-scale biogas reactor experiment. Two treatment conditions were used simulating total ammonia nitrogen concentrations of 4.9 and 8.0 g/L with four replicate reactors. Each reactor was monitored concerning methane generation and microbial composition using 16S rRNA gene amplicon sequencing, while the transcriptional activity of the overall process was investigated by metatranscriptomic analysis. This allowed investigating the response of the microbial community in terms of species composition and transcriptional activity to a rapid upshift to high ammonia conditions. Clostridia and Methanomicrobiales dominated the microbial community throughout the entire experiment under both experimental conditions, while Methanosarcinales were only present in minor abundance. Transcription analysis demonstrated clostridial dominance with respect to genes encoding for enzymes of the hydrolysis step (cellulase, EC 3.2.1.4) as well as dominance of key genes for enzymes of the methanogenic pathway (methyl-CoM reductase, EC 2.8.4.1; heterodisulfide reductase, EC 1.8.98.1). Upon ammonia shock, the selected marker genes showed significant changes in transcriptional activity. Cellulose hydrolysis as well as methanogenesis were significantly reduced at high ammonia concentrations as indicated by reduced transcription levels of the corresponding genes. Based on these experiments we concluded that, apart from the methanogenic archaea, hydrolytic cellulose-degrading microorganisms are negatively affected by high ammonia concentrations. Further, Acholeplasma and Erysipelotrichia showed lower abundance under increased ammonia concentrations and thus might serve as indicator species for an earlier detection in order to counteract against ammonia crises.

Deterministic Processes Drive the Microbial Assembly During the Recovery of an Anaerobic Digester after a Severe Ammonia Shock

“…The acetate was probably oxidised by syntrophic acetate oxidisers into H2 and CO2 directly consumed by the hydrogenotrophic archaea. The modification of the methanogenic pathway under ammonia inhibition was already observed in previous studies (Fischer et al, 2019).…”

A biogeographic 16S rRNA survey of bacterial communities of ureolytic biomineralization from California public restrooms

“…when compared to flush-type urinals [45][46][47]. In biogas reactors, Firmicutes dominated the community composition in environments with total ammoniacal nitrogen concentrations (TAN) ranging from 2.4 to 4.2 g/L [47].…”

Anaerobic Digestion of Blood from Slaughtered Livestock: A Review

“…Immediate effects of ammonia shock, resulting from protein-rich feed, on the transcription and composition of a biogas reactor microbiome were assessed by Fisher et al [84] using 16S rRNA gene amplicon sequencing. Clostridia and Bacteroidia were the first and second most dominant classes in the digester.…”