Investigation of the diversity of homoacetogenic bacteria in mesophilic and thermophilic anaerobic sludges using the formyltetrahydrofolate synthetase gene

Abstract

Homoacetogenic bacteria are strict anaerobes capable of autotrophic growth on H(2)/CO(2) or CO, and of heterotrophic growth on a wide range of sugars, alcohols, methoxylated aromatic compounds and one carbon compounds, yielding acetate as their sole metabolic end-product. Batch activity tests on anaerobic granular sludge, using H(2)/CO(2) as a substrate and 2-bromoethanesulfonate (BES) as a specific methanogenic inhibitor revealed that H(2)/CO(2) conversion and concomitant acetate production commenced only after a lag period of 60-100 h. This finding suggests that the homoacetogenic population of digester sludge could be maintained by heterotrophic growth on sugars or other organic compounds, rather than by autotrophic growth on H(2)/CO(2). In the present study, two upflow anaerobic sludge bed (UASB) reactors were operated at 37 degrees C and 55 degrees C for two distinct trial periods, each characterised by the application of influents designed to enrich for homoacetogenic bacteria. Specific primers designed for the amplification of the functional gene encoding formyltetrahydrofolate synthetase (FTHFS), a key enzyme in the acetyl-CoA pathway of acetogenesis, were used as a specific probe for acetogenic bacteria. The diversity of acetogens in the granular sludge cultivated in each reactor was revealed by application of FTHFS targeted PCR. Results show that biomass acetogenic composition was dependent upon the operational temperature of the reactor and the substrate supplied as influent.

Volatile fatty acids productions by mesophilic and thermophilic sludge fermentation: Biological responses to fermentation temperature

“…It was revealed by FTHFS clone libraries that homoacetogens mainly belonged to two phyla, Firmicutes and Proteobacteria (Ryan et al, 2008). In this study, MR and TR of semi-continuous tests had similar abundances of Firmicutes (18.3% in MR and 20.2% in TR), but the abundance of Proteobacteria in TR was more than 10% higher than MR (Fig.…”

“…A key enzyme in this CO 2 fixation pathway, formyltetrahydrofolate synthase (FTHFS), is conservative in structure and function (Xu et al, 2009). So the gene encoding FTHFS combined with clone library or real-time PCR assay can be used to identify and enumerate homoacetogens (Ryan et al, 2008;Xu et al, 2009). Though it was found that homoacetogens favored low temperature (Kotsyurbenko et al, 2001), FTHFS clone libraries revealed that they could have high diversity under mesophilic and thermophilic conditions (Ryan et al, 2008;Siriwongrungson et al, 2007).…”

“…So the gene encoding FTHFS combined with clone library or real-time PCR assay can be used to identify and enumerate homoacetogens (Ryan et al, 2008;Xu et al, 2009). Though it was found that homoacetogens favored low temperature (Kotsyurbenko et al, 2001), FTHFS clone libraries revealed that they could have high diversity under mesophilic and thermophilic conditions (Ryan et al, 2008;Siriwongrungson et al, 2007). However, up to now little has been known about homoacetogens abundances under mesophilic and thermophilic conditions, and their relationships with the fermented VFAs are also needed to be investigated.…”

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

“…Degenerated primers, designed to target a functional gene encoding a key enzyme in this pathway, 10-formyltetrahydrofolate synthetase (FTHFS) (11), have been used in several investigations to study acetogenic populations in different environments, such as salt marshes (12), hindguts (19), anaerobic sludge (21), human faeces (17) and microbial electrolysis cells (18).…”

Presence of Novel, Potentially Homoacetogenic Bacteria in the Rumen as Determined by Analysis of Formyltetrahydrofolate Synthetase Sequences from Ruminants

“…At present, only a limited number of FTHFS sequences have been deposited in databases, and the vast majority of them are partial sequences retrieved from complex microbial communities. FTHFS sequences have been surveyed in sludge (39,43,54), termites (40,44), salt marsh plant roots (21), horse manure (22), cow manure, freshwater sediment, rice field soil, and sewage (54), but so far only one study has investigated bovine ruminal FTHFS sequences (30). The rumen FTHFS sequences had low levels of similarity to the FTHFS sequences of known homoacetogens and could be sequences of novel homoacetogens.…”