Methanogen

About: Methanogen is a research topic. Over the lifetime, 1146 publications have been published within this topic receiving 48254 citations.

Microbial community dynamics in batch high-solid anaerobic digestion of food waste under mesophilic conditions.

Abstract: Microbial community shifts, associated with performance data, were investigated in an anaerobic batch digester treating high-solid food waste under mesophilic conditions using, a combination of molecular techniques and chemical analysis methods. The batch process was successfully operated with an organic removal efficiency of 44.5% associated with a biogas yield of 0.82 L/g VSremoval. Microbial community structures were examined by denaturing gel gradient electrophoresis. Clostridium and Symbiobacterium organisms were suggested to be mainly responsible for the organic matter catabolism in hydrolysis and acidogenesis reactions. The dynamics of archaeal and methanogenic populations were monitored using real-time PCR targeting 16S rRNA genes. Methanosarcina was the predominant methanogen, suggesting that the methanogenesis took place mainly via an aceticlastic pathway. Hydrogenotrophic methanogens were also supported in high-solid anaerobic digestion of food waste through syntrophism with syntrophic bacterium. Microbial community shifts showed good agreement with the performance parameters in anaerobic digestion, implying the possibility of diagnosing a high-solid anaerobic digestion process by monitoring microbial community shifts. On the other hand, the batch results could be relevant to the start-up period of a continuous system and could also provide useful information to set up a continuous operation.

Alamethicin Suppresses Methanogenesis and Promotes Acetogenesis in Bioelectrochemical Systems

Abstract: Microbial electrosynthesis (MES) systems with mixed cultures often generate a variety of gaseous and soluble chemicals. Methane is the primary end product in mixed-culture MES because it is the thermodynamically most favorable reduction product of CO 2 . Here, we show that the peptaibol alamethicin selectively suppressed the growth of methanogens in mixed-culture MES systems, resulting in a shift of the solution and cathode communities to an acetate-producing system dominated by Sporomusa, a known acetogenic genus in MES systems. Archaea in the methane-producing control were dominated by Methanobrevibacter species, but no Archaea were detected in the alamethicin-treated reactors. No methane was detected in the mixed-culture reactors treated with alamethicin over 10 cycles (∼3 days each). Instead, acetate was produced at an average rate of 115 nmol ml −1 day −1 , similar to the rate reported previously for pure cultures of Sporomusa ovata on biocathodes. Mixed-culture control reactors without alamethicin generated methane at nearly 100% coulombic recovery, and no acetate was detected. These results show that alamethicin is effective for the suppression of methanogen growth in MES systems and that its use enables the production of industrially relevant organic compounds by the inhibition of methanogenesis.

Acetate, a key intermediate in methanogenesis

Abstract: Acetate is the chief precursor of methane in anaerobic fermentations. Methane can be formed from H 2 and CO 2 by most methanogenic bacteria, but these substrates can also be converted to acetate by Clostridium aceticum , isolated from sludge. Its activity may increase the fraction of methane arising from acetate. Anaerobic 2% Ca acetate mineral enrichments forming methane were transferred weekly with a one-sixth volume inoculum. The rate of methane production was 9 μmoles ml −1 day −1 . Methanosarcina barkeri was the chief methanogen in the enrichment but numerous non-methanogens were present, three of which were isolated. In pure cultures of M. barkeri in medium supplemented with trypticase and yeast extract the rate of methanogenesis was 20 ymoles ml −1 day −1 , and similar supplementation of the enrichment culture increased the rate from 9 to 23 μmoles ml −1 day −1 . The rate of methane production was affected not only by M . barkeri but also by the non-methanogens in the enrichment. Microbiological analyses of methanogenic ecosystems is recommended as a means to provide clues of value in practical applications.

The effect of methanogen growth on mineral substrates: will Ni markers of methanogen‐based communities be detectable in the rock record?

Abstract: Methanogens, thought to be present on early Earth, have a high requirement for Ni, suggesting that Ni utilization could be a potential biosignature for methanogens if enhanced Ni extraction from surrounding minerals accompanies methanogenic growth. To test the potential for such Ni extraction from minerals by methanogens, Ni release from Ni-containing silicate glass was measured in Ni-free growth medium in the presence of the methanogen Methanothermobacter thermoautotrophicus (average pH ∼ 7.0) and observed to be higher than an abiotic control (average pH ∼ 6.8). However, batch dissolution experiments and a siderophore assay indicate that cell exudates such as siderophores, low molecular weight organic acids, or lysates accompanying cell death are not responsible for the observed increase in Ni release rate. In addition, scanning electron microscopy (SEM) shows little to no evidence of direct microbe‐mineral interactions such as biofilms or pitting. Instead, comparison with abiotic experiments suggests that changes in pH due to CO 2 uptake may be responsible for enhanced dissolution in the presence of metabolizing cells. These results document that methanogens may not preferentially extract Ni from surrounding minerals although they may indirectly affect mineral reaction rates that are pH sensitive. Thus identifiable Ni biosignatures may not exist in the rock record to document the presence of methanogens on early Earth or Mars.