A review of Methanoculleus: a hydrogenotrophic methanogens frequently observed in anaerobic habitats
Summary:
Keywords: Methanoculleus, hydrogenotrophic pathway, methane production
Introduction:
Methane is an important greenhouse gas due to its capability of retaining heat and its release from many nature sources, including wetlands, fresh water or sea water sediments, and animal manure, etc. There are two main means of atmospheric methane production, biogenic and abiogenic. Since 70%-80% of atmospheric methane is of biological origin (Le Mer and Roger, 2001), research in microbiological methane productions is critical to control the release of methane. On the other side, methane is also a reproducible fuel. More anaerobic biological treatment …show more content…
Unlike Methanosaeta, Methanosarcina, and other acetoclastic or methylotrophic methanogens, which are capable of reducing carbon dioxide to methane through electrical connections with some bacteria, Methanoculleus often take hydrogenotrophic pathway, which involves the reduction of CO2 to CH4, utilizing H2 and reduced cofactors as electron donors (Goldman et al., 2009). As many hydrogenotrophic methanogens, some of the Methanoculleus are thought to be autotrophic, requiring only CO2, H2, and inorganic salts to produce energy through methanogenesis and synthesize biomass through CO2 fixation (Reeve et al., 1997).
Although Methanoculleus have been found constantly, knowledge of their roles and functions in the microbial community is still limited. This article reviews the characteristics of Methanoculleus and tries to understand their importance in both nature and biological treatment processes.
Physiology of Methanoculleus isolates:
In taxonomy, the hydrogenotrophic methanogens genus Methanoculleus belong to phylum Euryachaeota, class Methanomicrobia, order Methanomicrobiales, and family Methanomicrobiaceae.
By the year of 2016, there are 13 isolated and named Methanoculleus species (short as M. in this article): M. bourgensis, M. …show more content…
All the Methanoculleus cells were reported as irregular cocciod, with M. oldenburgensis as fimbriate irregular cocciod. No motility was observed for any of these cells. Cell sizes of the Methanoculleus species with validly published names are similar. Some major phenotypic differences were as follows: (1) Flagellation was observed with M. chikugoensis, M. horonobensis, M. marisnigri, M. palmolei, M. submarinus, and M. thermophilus while M. bourgensis, and M. olentangyi were reported no flagellation. (2) M. bourgensis, M. olentangyi, M. receptaculi, and M. thermophilus tend to survive in higher temperatures (higher than 30 oC) while the others have wider range of survival temperatures, as low as 10-25 oC. Nevertheless, except for M. chikugoensis and M. marisnigri, whose optimum temperatures are 25-30 and 20-25 oC respectively, all Methanoculleus have a higher optimum temperatures higher than 37 oC, with the optimized temperatures for M. receptaculi and M. thermophilus as 50-55 and 55 oC respectively, to be the highest. (3) The pH range of the Methanoculleus species are close to neutral, with optimum pH of M. receptaculi being 7.5-6.8 and it of M. oldenburgensis and M. taiwanensis being 8, slightly distinct from others. (4) The optimum NaCl tolerance are similarly comparatively low for all the Methanoculleus species apart from it of M. oldenburgensis
Summary:
Keywords: Methanoculleus, hydrogenotrophic pathway, methane production
Introduction:
Methane is an important greenhouse gas due to its capability of retaining heat and its release from many nature sources, including wetlands, fresh water or sea water sediments, and animal manure, etc. There are two main means of atmospheric methane production, biogenic and abiogenic. Since 70%-80% of atmospheric methane is of biological origin (Le Mer and Roger, 2001), research in microbiological methane productions is critical to control the release of methane. On the other side, methane is also a reproducible fuel. More anaerobic biological treatment …show more content…
Unlike Methanosaeta, Methanosarcina, and other acetoclastic or methylotrophic methanogens, which are capable of reducing carbon dioxide to methane through electrical connections with some bacteria, Methanoculleus often take hydrogenotrophic pathway, which involves the reduction of CO2 to CH4, utilizing H2 and reduced cofactors as electron donors (Goldman et al., 2009). As many hydrogenotrophic methanogens, some of the Methanoculleus are thought to be autotrophic, requiring only CO2, H2, and inorganic salts to produce energy through methanogenesis and synthesize biomass through CO2 fixation (Reeve et al., 1997).
Although Methanoculleus have been found constantly, knowledge of their roles and functions in the microbial community is still limited. This article reviews the characteristics of Methanoculleus and tries to understand their importance in both nature and biological treatment processes.
Physiology of Methanoculleus isolates:
In taxonomy, the hydrogenotrophic methanogens genus Methanoculleus belong to phylum Euryachaeota, class Methanomicrobia, order Methanomicrobiales, and family Methanomicrobiaceae.
By the year of 2016, there are 13 isolated and named Methanoculleus species (short as M. in this article): M. bourgensis, M. …show more content…
All the Methanoculleus cells were reported as irregular cocciod, with M. oldenburgensis as fimbriate irregular cocciod. No motility was observed for any of these cells. Cell sizes of the Methanoculleus species with validly published names are similar. Some major phenotypic differences were as follows: (1) Flagellation was observed with M. chikugoensis, M. horonobensis, M. marisnigri, M. palmolei, M. submarinus, and M. thermophilus while M. bourgensis, and M. olentangyi were reported no flagellation. (2) M. bourgensis, M. olentangyi, M. receptaculi, and M. thermophilus tend to survive in higher temperatures (higher than 30 oC) while the others have wider range of survival temperatures, as low as 10-25 oC. Nevertheless, except for M. chikugoensis and M. marisnigri, whose optimum temperatures are 25-30 and 20-25 oC respectively, all Methanoculleus have a higher optimum temperatures higher than 37 oC, with the optimized temperatures for M. receptaculi and M. thermophilus as 50-55 and 55 oC respectively, to be the highest. (3) The pH range of the Methanoculleus species are close to neutral, with optimum pH of M. receptaculi being 7.5-6.8 and it of M. oldenburgensis and M. taiwanensis being 8, slightly distinct from others. (4) The optimum NaCl tolerance are similarly comparatively low for all the Methanoculleus species apart from it of M. oldenburgensis