The ability of bacteria to use natural carbon sources greatly affects their growth and survival in the environment. Bacteria have evolved versatile abilities to use environmental carbon sources, but their diversity and assimilation pathways remain largely unexplored. Trans-aconitic acid, a geometric isomer of cis-aconitic acid involved in the tricarboxylic acid cycle, has long been considered a natural carbon source metabolizable by bacteria. However, its catabolism and ecological role in linking bacterial interactions with the environments remain unclear. Here, we identify a regulatory system in Bacillus velezensis FZB42 that is capable of sensing and catabolizing trans-aconitic acid. The system consists of a tar operon, an adjacent positive regulatory gene tarR, and a shared promoter. After receiving the trans-aconitic acid signal, the TarR protein interacts directly with the promoter, initiating the expression of the membrane transporter TarB and aconitate isomerase TarA encoded by the operon, which function in importing the trans-aconitic acid and isomerizing it into the central intermediate cis-aconitic acid. Subsequent soil colonization experiments reveal that trans-aconitic acid assimilating ability can give its coding bacteria a growth and competitive advantage. Bioinformatics analyses coupled with bacterial isolation experiments further show that the assimilation system of trans-aconitic acid is widely distributed in the bacterial domain, and its assimilating bacteria also extensively distributed in nature, indicating an important role of trans-aconitic acid metabolism in bacterial carbon acquisition. This work emphasizes the importance of metabolic adaptation to environmental carbon sources for bacterial survival and may provide inspiration for engineering microbes with enhanced environmental competitiveness.

中文翻译：

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反式阿炮酸同化系统作为一种广泛的环境适应细菌机制


细菌利用天然碳源的能力极大地影响了它们在环境中的生长和生存。细菌已经进化出利用环境碳源的多种能力，但它们的多样性和同化途径在很大程度上仍未得到探索。反式乌头酸是参与三羧酸循环的顺式乌头酸的几何异构体，长期以来一直被认为是可被细菌代谢的天然碳源。然而，它在将细菌相互作用与环境联系起来的分解代谢和生态作用仍不清楚。在这里，我们在 Bacillus velezensis FZB42 中鉴定了一个能够感应和分解代谢反式乌头酸的调节系统。该系统由一个 tar 操纵子、一个相邻的阳性调节基因 tarR 和一个共享启动子组成。接收到反式乌头酸信号后，TarR 蛋白直接与启动子相互作用，启动由操纵子编码的膜转运蛋白 TarB 和乌头酸异构酶 TarA 的表达，其功能是输入反式乌头酸并将其异构化到中央中间体顺式乌头酸中。随后的土壤定植实验表明，反式乌头酸同化能力可以赋予其编码细菌生长和竞争优势。生物信息学分析结合细菌分离实验进一步表明，反式乌云酸的同化系统广泛分布在细菌领域，其同化细菌在自然界中也广泛分布，表明反式乌云酸代谢在细菌碳获取中具有重要作用。 这项工作强调了代谢适应环境碳源对细菌生存的重要性，并可能为具有增强环境竞争力的工程微生物提供灵感。