Laboratory of Proteomics and Microbiology, Research Institute for Biosciences, University of Mons, Avenue du champs de Mars, 6 (Pentagone 3B), 7000, Mons, Belgium.
Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA.
BMC Microbiol. 2020 May 20;20(1):126. doi: 10.1186/s12866-020-01814-7.
The great metabolic versatility of the purple non-sulfur bacteria is of particular interest in green technology. Rhodospirillum rubrum S1H is an α-proteobacterium that is capable of photoheterotrophic assimilation of volatile fatty acids (VFAs). Butyrate is one of the most abundant VFAs produced during fermentative biodegradation of crude organic wastes in various applications. While there is a growing understanding of the photoassimilation of acetate, another abundantly produced VFA, the mechanisms involved in the photoheterotrophic metabolism of butyrate remain poorly studied.
In this work, we used proteomic and functional genomic analyses to determine potential metabolic pathways involved in the photoassimilation of butyrate. We propose that a fraction of butyrate is converted to acetyl-CoA, a reaction shared with polyhydroxybutyrate metabolism, while the other fraction supplies the ethylmalonyl-CoA (EMC) pathway used as an anaplerotic pathway to replenish the TCA cycle. Surprisingly, we also highlighted a potential assimilation pathway, through isoleucine synthesis and degradation, allowing the conversion of acetyl-CoA to propionyl-CoA. We tentatively named this pathway the methylbutanoyl-CoA pathway (MBC). An increase in isoleucine abundance was observed during the early growth phase under butyrate condition. Nevertheless, while the EMC and MBC pathways appeared to be concomitantly used, a genome-wide mutant fitness assay highlighted the EMC pathway as the only pathway strictly required for the assimilation of butyrate.
Photoheterotrophic growth of Rs. rubrum with butyrate as sole carbon source requires a functional EMC pathway. In addition, a new assimilation pathway involving isoleucine synthesis and degradation, named the methylbutanoyl-CoA (MBC) pathway, could also be involved in the assimilation of this volatile fatty acid by Rs. rubrum.
紫色非硫细菌的巨大代谢多样性在绿色技术中特别有趣。红螺菌 S1H 是一种 α-变形菌，能够异养光合同化挥发性脂肪酸（VFAs）。丁酸是在各种应用中发酵生物降解粗有机废物时产生的最丰富的 VFA 之一。虽然人们对另一种大量产生的 VFA 乙酸盐的光同化作用有了越来越多的了解，但丁酸的异养光合作用代谢所涉及的机制仍研究甚少。
在这项工作中，我们使用蛋白质组学和功能基因组学分析来确定参与丁酸光同化作用的潜在代谢途径。我们提出，一部分丁酸转化为乙酰辅酶 A，这一反应与聚羟基丁酸代谢共享，而另一部分丁酸提供乙基丙二酰辅酶 A（EMC）途径，作为补充 TCA 循环的同化途径。令人惊讶的是，我们还强调了一种潜在的同化途径，通过异亮氨酸合成和降解，允许将乙酰辅酶 A 转化为丙酰辅酶 A。我们暂命名该途径为甲基丁酰辅酶 A 途径（MBC）。在丁酸条件下的早期生长阶段观察到异亮氨酸丰度增加。然而，尽管 EMC 和 MBC 途径似乎同时被使用，但全基因组突变体适应性测定突出了 EMC 途径是丁酸同化所必需的唯一途径。
以丁酸为唯一碳源的红螺菌的异养光合生长需要功能性 EMC 途径。此外，涉及异亮氨酸合成和降解的新同化途径，命名为甲基丁酰辅酶 A（MBC）途径，也可能参与红螺菌对这种挥发性脂肪酸的同化。
