Changes in the Acetogenic Population in a Mesophilic Anaerobic Digester in Response to Increasing Ammonia Concentration

Abstract

Changes in the acetogenic population were investigated in an experimental laboratory-scale biogas reactor (37°C) subjected to gradually elevated ammonia levels (0.8 to 6.9 g NH4 + -N L −1 ). A shift from aceticlastic acetate degradation to syntrophic acetate oxidation had previously been confirmed in this reactor. In a parallel control reactor, operating at constant ammonia levels (0.65-0.90 g NH 4 + -N L −1 ), acetate degradation proceeded via the aceticlastic pathway throughout the operating period (660 d). The acetogenic populations in the reactors were analysed using degenerated primers designed to target the functional gene encoding a key enzyme of the acetyl-CoA pathway, 10-formyltetrahydrofolate synthetase (FTHFS). The analysis consisted of terminal restriction fragment length polymorphism (T-RFLP) analysis coupled with the construction of clone libraries, and quantitative PCR (qPCR) analysis. The T-RFLP data obtained were statistically analysed by non-metric multidimensional scaling. The most abundant FTHFS genes recovered in the clone libraries were assigned to terminal restriction fragments of the T-RFLP profile. The results of the investigation clearly indicated that increased ammonia concentration substantially influenced the putative acetogenic population structure and caused two distinct shifts of the most abundant members; however, the identity of the dominating species remains unknown, as none of the genes had been identified previously. Despite the shifts in the population, the qPCR analysis revealed a relatively stable abundance of the acetogenic population throughout the operation.

Anaerobic co-digestion of kitchen waste and pig manure with different mixing ratios

“…In a previous study, it was found that slight inhibition happened until the ammonia nitrogen concentration was tested to be 3000 mg/L in a piggery waste experiment (50). It was also reported that for dealing with organic municipal wastes, the process remained stable and the methane yield kept normal at the pH value of 7.9 and ammonia nitrogen concentration reached 3300 mg/L (51). Some researchers also suggested that free ammonia which was determined by three parameters (total ammonia concentration, temperature and pH) was the most important component causing ammonia inhibition (21,25) and the advised value of free ammonia was below 150 mg/L (52) or at least no more than 220 mg/L which was the half toxic inhibition constant (53).…”

Agricultural biogas production in Germany - from practice to microbiology basics

“…A recent metaproteome study came to very similar conclusions at the protein level [80]. Also at high ammonia levels, there are many lines of evidence confirming that strictly hydrogenotrophic Archaea with different syntrophic bacterial partners are the workhorse teams producing methane via the acetate oxidation pathway (SAO) at meso-and thermophilic conditions [48,[81][82][83]. The most important reason for these strain-and stressinduced population shifts is probably that particularly Methanobacterium and Methanothermobacter archaea have higher growth rates than Methanosarcina representatives and are thus more capable of coping with the dilution rate under the influence of stress factors in flow-through processes.…”

Methanogenic Population and CH 4 Production in Swedish Dairy Cows Fed Different Levels of Forage

“…The program used was as follows: initial temperature of 95°C for 7 min followed by 55 cycles of 95°C for 40 s, 58°C (for total methanogens, 66°C, and for the order Methanobacteriales, 60°C) for 60 s, and 72°C for 40 s. DNA standard curves were prepared from pure cultures of Methanobrevibacter ruminantium DSMZ 1093 and Methanoculleus bourgensis DSMZ 3045 using the specific primer sets for Methanobacteriales, Methanomicrobiales, and total methanogens. The standard was prepared as described in the work of Westerholm et al (40). The specificity of the target PCR product was estimated by melt curve analysis, which consisted of 50 gradual denaturation cycles.…”