Microbial Community Dynamics and Stability during an Ammonia-Induced Shift to Syntrophic Acetate Oxidation

Abstract

g Anaerobic digesters rely on the diversity and distribution of parallel metabolic pathways mediated by complex syntrophic microbial communities to maintain robust and optimal performance. Using mesophilic swine waste digesters, we experimented with increased ammonia loading to induce a shift from aceticlastic methanogenesis to an alternative acetate-consuming pathway of syntrophic acetate oxidation. In comparison with control digesters, we observed shifts in bacterial 16S rRNA gene content and in functional gene repertoires over the course of the digesters' 3-year operating period. During the first year, under identical startup conditions, all bioreactors mirrored each other closely in terms of bacterial phylotype content, phylogenetic structure, and evenness. When we perturbed the digesters by increasing the ammonia concentration or temperature, the distribution of bacterial phylotypes became more uneven, followed by a return to more even communities once syntrophic acetate oxidation had allowed the experimental bioreactors to regain stable operation. The emergence of syntrophic acetate oxidation coincided with a partial shift from aceticlastic to hydrogenotrophic methanogens. Our 16S rRNA gene analysis also revealed that acetatefed enrichment experiments resulted in communities that did not represent the bioreactor community. Analysis of shotgun sequencing of community DNA suggests that syntrophic acetate oxidation was carried out by a heterogeneous community rather than by a specific keystone population with representatives of enriched cultures with this metabolic capacity.

Comparing the inhibitory thresholds of dairy manure co-digesters after prolonged acclimation periods: Part 2 – correlations between microbiomes and environment

“…S4). As noted above, Werner et al (2014) previously observed a decrease in community evenness with initial ammonia stress in swine waste anaerobic digesters, which also negatively affected reactor performance. However, performance eventually recovered, and this recovery coincided with a shift in the microbiome towards syntrophic acetate oxidation and greater community evenness.…”

“…High free ammonia concentrations have previously been shown to inhibit acetoclastic methanogens (Angenent et al, 2002;Werner et al, 2014), which can lead to a build-up of acetate. The buildup of acetate can make beta-oxidation of higher-chain VFAs less thermodynamically favorable and lead to an accumulation of higherchain VFAs in the reactor.…”

“…S4). Previously, Werner et al (2014) noted that perturbations due to ammonia stress led to an initial decline in community evenness in swine manure anaerobic digesters. As total and free ammonia levels increased in the reactor during CT-II, the microbiome clearly diverged from the other reactor microbiomes along PC2 in the PCoA (Fig.…”

Changing Feeding Regimes To Demonstrate Flexible Biogas Production: Effects on Process Performance, Microbial Community Structure, and Methanogenesis Pathways

“…Syntrophic acetate-oxidizing bacteria (SAOB) capable of SAO were detected in laboratory-scale mesophilic CSTRs with high ammonia concentrations (37) and in industrial mesophilic or thermophilic CSTRs (38). Another recent finding has also shown that high levels of ammonia in mesophilic swine waste digesters induce a shift from AM to SAO and the latter is carried out by a dynamic and heterogeneous community with this metabolic capacity rather than known defined cultures of SAOB (39). Further research on the identity of the bacterial communities in our DDGS-fed reactors would provide a better insight into the role of each functional group within the bacterial community.…”

Waste Conversion into n-Caprylate and n-Caproate: Resource Recovery from Wine Lees Using Anaerobic Reactor Microbiomes and In-line Extraction

“…Anaerobic digesters employ reactor microbiomes (open cultures of microbial consortia) to convert complex organic wastes into methane-rich biogas, which is a reliable source of renewable electricity (Weiland, 2006). Reactor microbiomes can be shaped for various processes and products because they are reproducible and predictable (Werner et al, 2011, 2014; Vanwonterghem et al, 2014). In anaerobic digesters, reactor microbiomes hydrolyze complex molecules into monomers during the first step of a four-step anaerobic food web.…”