Although of limited metabolic diversity, methanogenic archaea or methanogens possess great phylogenetic and ecological diversity. Only three types of methanogenic pathways are known: CO(2)-reduction, methyl-group reduction, and the aceticlastic reaction. Cultured methanogens are grouped into five orders based upon their phylogeny and phenotypic properties. In addition, uncultured methanogens that may represent new orders are present in many environments. The ecology of methanogens highlights their complex interactions with other anaerobes and the physical and chemical factors controlling their function.

Metabolic, phylogenetic, and ecological diversity of the methanogenic archaea.

Methanosarcina: the rediscovered methanogen for heavy duty biomethanation.

Effect of process temperature on bacterial and archaeal communities in two methanogenic bioreactors treating organic household waste.

Microbial characteristics in anaerobic digestion process of food waste for methane production–A review

Anaerobic digestion is the method of wastes treatment aimed at a reduction of their hazardous effects on the biosphere. The mutualistic behavior of various anaerobic microorganisms results in the decomposition of complex organic substances into simple, chemically stabilized compounds, mainly methane and CO2. The conversions of complex organic compounds to CH4 and CO2 are possible due to the cooperation of four different groups of microorganisms, that is, fermentative, syntrophic, acetogenic, and methanogenic bacteria. Microbes adopt various pathways to evade from the unfavorable conditions in the anaerobic digester like competition between sulfate reducing bacteria (SRB) and methane forming bacteria for the same substrate. Methanosarcina are able to use both acetoclastic and hydrogenotrophic pathways for methane production. This review highlights the cellulosic microorganisms, structure of cellulose, inoculum to substrate ratio, and source of inoculum and its effect on methanogenesis. The molecular techniques such as DGGE (denaturing gradient gel electrophoresis) utilized for dynamic changes in microbial communities and FISH (fluorescent in situ hybridization) that deal with taxonomy and interaction and distribution of tropic groups used are also discussed.

https://downloads.hindawi.com/journals/tswj/2014/183752.pdf

Microbial ecology of anaerobic digesters: the key players of anaerobiosis.

Methanosarcina species with a high maximum specific growth rate (mumax) and high half-saturation coefficient (KS) and Methanosaeta species with a low mumax and low KS are the only known aceticlastic methanogens. Because of Methanosaeta's low KS, the low acetate concentrations in conventional, mesophilic anaerobic digestion yield Methanosaeta dominance. However, Methanosarcina absorbs increases in acetate more efficiently and thus promotes more stable digestion. This paper tests the hypothesis that decreasing digester feeding frequencies can increase Methanosarcina predominance. Two acetate-fed reactors were established at a 17-day solids retention time. One reactor was fed hourly, and one was fed once daily. Microscopic and molecular methods were used to verify that the hourly fed reactor enriched for Methanosaeta, while the daily fed reactor enriched for Methanosarcina. Growth and substrate-use kinetics were measured for each reactor. A digester overload condition was simulated, and the Methanosarcina-enriched reactor was found to perform better than the Methanosaeta-enriched reactor. These findings indicate that Methanosarcina dominance can be achieved with infrequent feedings, leading to more stable digestion.

https://www.jstor.org/stable/info/25053536

Growth kinetics and competition between Methanosarcina and Methanosaeta in mesophilic anaerobic digestion.

Monitoring the role of aceticlasts in anaerobic digestion: Activity and capacity

The Growth Kinetics and Competition Between Methanosarcina and Methanosaeta in Mesophilic Anaerobic Digestion

Methanosarcina species with a high maximum specific growth rate (^max) and high half-saturation coefficient (Ks) and Methano saeta species with a low |xmax and low ^s are the only known aceticlastic methanogens. Because of Methanosaeta's low Ks, the low acetate concentrations in conventional, mesophilic anaerobic digestion yield Methanosaeta dominance. However, Methanosarcina absorbs increases in acetate more efficiently and thus promotes more stable digestion. This paper tests the hypothesis that decreasing digester feeding frequencies can increase Methanosarcina predominance. Two acetate-fed reactors were established at a 17-day solids retention time. One reactor was fed hourly, and one was fed once daily. Microscopic and molecular methods were used to verify that the hourly fed reactor enriched for Methanosaeta, while the daily fed reactor enriched for Methanosarcina. Growth and substrate-use kinetics were mea sured for each reactor. A digester overload condition was simulated, and the Methanosarcina-enriched reactor was found to perform better than the Methanosaeta-enriched reactor. These findings indicate that Methanosarcina dominance can be achieved with infrequent feedings, leading to more stable digestion. Water Environ. Res., 78, 486 (2006).

Anne Conklin

Papers

Growth kinetics and competition between Methanosarcina and Methanosaeta in mesophilic anaerobic digestion.

Monitoring the role of aceticlasts in anaerobic digestion: Activity and capacity

The Growth Kinetics and Competition Between Methanosarcina and Methanosaeta in Mesophilic Anaerobic Digestion

Growth Kinetics and Competition Between Methanosarcina and Methanosaeta in

Monitoring the Role of Acetoclasts in Anaerobic Digestion: Activity and Capacity