Sprenger Wander W, Hackstein Johannes H P, Keltjens Jan T
Department of Microbiology, Faculty of Science, Radboud University of Nijmegen, Nijmegen, The Netherlands.
FEMS Microbiol Ecol. 2007 May;60(2):266-75. doi: 10.1111/j.1574-6941.2007.00287.x. Epub 2007 Mar 16.
Methanomicrococcus blatticola is an obligately anaerobic methanogen that derives the energy for growth exclusively from the reduction of methylated compounds to methane with molecular hydrogen as energy source. Competition for methanol (concentration below 10 microM) and H(2) (concentration below 500 Pa), as well as oxidative stress due to the presence of oxygen are likely to occur in the peripheral region of the cockroach hindgut, the species' normal habitat. We investigated the ecophysiological properties of M. blatticola to explain how it can successfully compete for its methanogenic substrates. The organism showed affinities for methanol (K(m)=5 microM; threshold<1 microM) and hydrogen (K(m)=200 Pa; threshold <0.7 Pa) that are superior to other methylotrophic methanogens (Methanosphaera stadtmanae, Methanosarcina barkeri) investigated here. Thermodynamic considerations indicated that 'methanol respiration', i.e. the use of methanol as the terminal electron acceptor, represents an attractive mode of energy generation, especially at low hydrogen concentrations. Methanomicrococcus blatticola exploits the opportunities by specific growth rates (>0.2 h(-1)) and specific growth yields (up to 7 g of dry cells per mole of methane formed) that are particularly high within the realm of mesophilic methanogens. Upon oxygen exposure, part of the metabolic activity may be diverted into oxygen removal, thus establishing appropriate anaerobic conditions for survival and growth.
拟粪甲烷微球菌是一种专性厌氧产甲烷菌，其生长所需能量仅来自于以分子氢为能源将甲基化化合物还原为甲烷。在蟑螂后肠的外周区域（该物种的正常栖息地），可能会发生对甲醇（浓度低于10微摩尔）和氢气（浓度低于500帕）的竞争，以及由于氧气存在而产生的氧化应激。我们研究了拟粪甲烷微球菌的生态生理特性，以解释它如何能够成功地竞争产甲烷底物。该生物体对甲醇（米氏常数K(m)=5微摩尔；阈值<1微摩尔）和氢气（K(m)=200帕；阈值<0.7帕）的亲和力优于这里研究的其他甲基营养型产甲烷菌（史氏甲烷球形菌、巴氏甲烷八叠球菌）。热力学考虑表明，“甲醇呼吸”，即以甲醇作为末端电子受体，是一种有吸引力的能量产生方式，尤其是在低氢气浓度下。拟粪甲烷微球菌通过特定生长速率（>0.2 h(-1)）和特定生长产率（每形成一摩尔甲烷最多可产生7克干细胞）利用这些机会，在嗜温产甲烷菌范围内，这些速率和产率特别高。暴露于氧气后，部分代谢活性可能会转向去除氧气，从而为生存和生长建立适当的厌氧条件。
