Physiological and genetic basis for self‐aggregation of a thermophilic hydrogenotrophic methanogen, M ethanothermobacter strain CaT 2

• Published in: Environmental microbiology reports Vol. 6; no. 3; pp. 268 - 277
• Main Authors: Kosaka, Tomoyuki, Toh, Hidehiro, Fujiyama, Asao, Sakaki, Yoshiyuki, Watanabe, Keiji, Meng, Xian‐Ying, Hanada, Satoshi, Toyoda, Atsushi
• Format: Journal Article
• Language: English
• Published: 01.06.2014
• ISSN: 1758-2229; 1758-2229
• DOI: 10.1111/1758-2229.12128

Summary Several thermophilic hydrogenotrophic methanogens naturally aggregate in their habitats in association with hydrogen‐producing bacteria for efficient transfer of the methane fermentation intermediates to produce methane. However, physiology of aggregation and the identity of aggregation‐specific genes remain to be elucidated. Here, we isolated and characterized a hydrogen and formate‐utilizing M ethanothermobacter sp. CaT 2 that is capable of self‐aggregation and utilizing formate. CaT 2 produced methane from propionate oxidation in association with a syntrophic propionate‐oxidizing bacterium faster than other methanogens, including M ethanothermobacter thermautotrophicus Δ H and M ethanothermobacter thermautotrophicus   Z ‐245. CaT 2 also aggregated throughout the culture period and was coated with polysaccharides, which was not found on the Δ H and Z ‐245 cells. Sugar content (particularly of rhamnose and mannose) was also higher in the CaT 2 cells than the Δ H and Z ‐245 cells. Comparative genomic analysis of CaT 2 indicated that four candidate genes, all of which encode glycosyltransferase, were involved in aggregation of CaT 2. Transcriptional analysis showed that one glycosyltransferase gene was expressed at relatively high levels under normal growth conditions. The polysaccharide layer on the CaT 2 cell surface, which is probably assembled by these glycosyltransferases, may be involved in cell aggregation.