甲烷氧化细菌催化二氧化碳生物合成甲醇的研究

Biosynthesis of Methanol from Carbon Dioxide by Methanotrophic Bacteria

甲烷氧化细菌中包含的甲烷单加氧酶(MMO)、甲醇脱氢酶(ADH)、甲醛脱氢酶(FaldDH)、甲酸脱氢酶(FateDH)经过一系列反应能够把甲烷深度氧化生成二氧化碳,并生成一定的能量物质.把二氧化碳还原为甲醇是一个需要能量的过程,目前还没有已知的有机体在温和条件下完成这一反应.研究发现,甲基弯菌MethylosinustrichosporiumIMV3011可以催化二氧化碳生物转化生成甲醇.在休眠的悬浮细胞中充入二氧化碳后,反应一段时间在反应液中检测到了甲醇.二氧化碳转化成甲醇是一个需要能量推动的反应,为了补充反应所消耗的能量,反应一段时间后需要用甲烷进行再生,以恢复细胞中的还原当量NADH.我们进行了反应再生的交替连续批式反应,甲醇积累量能够维持在一个比较稳定的水平.理论上,反应不会增加温室效应,这是一个有效的、环境友好的、可恢复的反应过程.

Methanotrophs can oxidize methane to carbon dioxide through sequential reactions catalyzed by a series of enzymes including methane monooxygenase, methanol dehydrogenase, formaldehyde dehydrogenase, and formate dehydrogenase. Reducing carbon dioxide to methanol is an opposite reaction of methanol oxidation, which requires a considerable amount of energy. So far there are no known organisms whose normal biological role is reduction of carbon dioxide to methanol. In this communication, we report that bioconversion of carbon dioxide to methanol was successfully achieved using resting cells of methanotrophic bacteria of Methylosinus trichosporium IMV 3011 as biocatalysts. Extracellular methanol accumulation has been found in the carbon dioxide incubations. The conversion of carbon dioxide to methanol is energy-intensive and requires reducing equivalent to push the reaction along against energy laws. For long-term maintenance of methanol synthesis, methane was selected as a substrate for regeneration of reducing equivalent. By alternate reaction and regeneration, the results show that resting cell of M. trichosporium IMV 3011 can be used for many times to catalyze the reduction of carbon dioxide, in which the origin of the reducing equivalent is methane. It is possible to theoretically deduce that the overall reaction for methanol synthesis can be completed by biocatalysis using greenhouse gases (carbon dioxide and methane) as raw materials without adding hydrogen. This new route should be environmentally friendly and a selective process operating at room temperature and normal pressure. Also, it is theoretically possible that the overall reaction can produce methanol without adding to the greenhouse effect.