Department of Microbe-Plant Interactions, Faculty of Biology/Chemistry, University of Bremen, P.O. Box 330440, 28334 Bremen, Germany.
Mol Plant Microbe Interact. 2017 Oct;30(10):778-785. doi: 10.1094/MPMI-01-17-0013-R. Epub 2017 Jul 26.
The habitat of the nitrogen-fixing endophyte Azoarcus sp. strain BH72 is grass roots grown under waterlogged conditions that produce, under these conditions, ethanol. Strain BH72 is well equipped to metabolize ethanol, with eight alcohol dehydrogenases (ADHs), of which ExaA2 and ExaA3 are the most relevant ones. exaA2 and exaA3 cluster and are surrounded by genes encoding two-component regulatory systems (TCSs) termed ExaS-ExaR and ElmS-GacA. Functional genomic analyses revealed that i) expression of the corresponding genes was induced by ethanol, ii) the genes were also expressed in the rhizoplane or even inside of rice roots, iii) both TCSs were indispensable for growth on ethanol, and iv) they were important for competitiveness during rice root colonization. Both TCSs form a hierarchically organized ethanol-responsive signal transduction cascade with ExaS-ExaR as the highest level, essential for effective expression of the ethanol oxidation system based on ExaA2. Transcript and expression levels of exaA3 increased in tcs deletion mutants, suggesting no direct influence of both TCSs on its ethanol-induced expression. In conclusion, this underscores the importance of ethanol for the endophytic lifestyle of Azoarcus sp. strain BH72 and indicates a tight regulation of the ethanol oxidation system during root colonization.
固氮内生菌 Azoarcus sp. 菌株 BH72 的栖息地是生长在水淹条件下的草根，在这种条件下会产生乙醇。菌株 BH72 非常适合代谢乙醇，有 8 种醇脱氢酶（ADHs），其中 ExaA2 和 ExaA3 是最相关的两种。exaA2 和 exaA3 聚类并被编码两个组分调节系统（TCSs）的基因包围，这些基因分别称为 ExaS-ExaR 和 ElmS-GacA。功能基因组分析表明：i）相应基因的表达受乙醇诱导，ii）这些基因也在根际甚至在水稻根内表达，iii）这两个 TCSs 对乙醇生长是必不可少的，iv）它们对水稻根定殖期间的竞争力很重要。这两个 TCSs 形成了一个层次化的乙醇响应信号转导级联，以 ExaS-ExaR 为最高级，这对基于 ExaA2 的乙醇氧化系统的有效表达是必不可少的。在 tcs 缺失突变体中，exaA3 的转录和表达水平增加，表明这两个 TCSs 对其乙醇诱导表达没有直接影响。总之，这突显了乙醇对 Azoarcus sp. 菌株 BH72 内生生活方式的重要性，并表明在根定殖过程中对乙醇氧化系统进行了严格的调控。
