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Inaugural Article: Carbon dioxide fixation as a central redox cofactor recycling mechanism in bacteria

机译:开篇文章:二氧化碳固定是细菌中一个重要的氧化还原辅助因子回收机制

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摘要

The Calvin-Benson-Bassham cycle (Calvin cycle) catalyzes virtually all primary productivity on Earth and is the major sink for atmospheric CO2. A less appreciated function of CO2 fixation is as an electron-accepting process. It is known that anoxygenic phototrophic bacteria require the Calvin cycle to accept electrons when growing with light as their sole energy source and organic substrates as their sole carbon source. However, it was unclear why and to what extent CO2 fixation is required when the organic substrates are more oxidized than biomass. To address these questions we measured metabolic fluxes in the photosynthetic bacterium Rhodopseudomonas palustris grown with 13C-labeled acetate. R. palustris metabolized 22% of acetate provided to CO2 and then fixed 68% of this CO2 into cell material using the Calvin cycle. This Calvin cycle flux enabled R. palustris to reoxidize nearly half of the reduced cofactors generated during conversion of acetate to biomass, revealing that CO2 fixation plays a major role in cofactor recycling. When H2 production via nitrogenase was used as an alternative cofactor recycling mechanism, a similar amount of CO2 was released from acetate, but only 12% of it was reassimilated by the Calvin cycle. These results underscore that N2 fixation and CO2 fixation have electron-accepting roles separate from their better-known roles in ammonia production and biomass generation. Some nonphotosynthetic heterotrophic bacteria have Calvin cycle genes, and their potential to use CO2 fixation to recycle reduced cofactors deserves closer scrutiny.
机译:卡尔文-本森-巴萨姆循环(卡尔文循环)催化了地球上几乎所有的初级生产力,是大气中CO2的主要吸收者。 CO 2固定的一种不太受赞赏的功能是作为电子接受过程。众所周知,产氧光养细菌在以光为唯一能源和以有机底物为唯一碳源生长时,需要卡尔文循环来接受电子。但是,尚不清楚当有机底物比生物质更易被氧化时,为什么需要CO 2固定以及在何种程度上需要CO 2固定。为了解决这些问题,我们测量了由 13 C标记的乙酸盐生长的光合细菌紫红假单胞菌的代谢通量。 R. palustris代谢提供给CO2的22%乙​​酸盐,然后使用Calvin循环将68%的此CO2固定在细胞材料中。这种Calvin循环通量使R. palustris能够重新氧化将乙酸盐转化为生物质过程中产生的几乎一半的还原型辅因子,这表明CO2固定在辅因子循环中起着重要作用。当将通过固氮酶产生的氢气用作替代性辅因子回收机制时,乙酸盐会释放出相似量的二氧化碳,但加尔文循环只能重新吸收其​​中的12%。这些结果表明,N2固定和CO2固定具有电子接受作用,而在氨生产和生物质产生中它们的作用更为人所共知。一些非光合作用的异养细菌具有卡尔文循环基因,它们利用CO2固定来回收还原的辅因子的潜力值得进一步研究。

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