Broad-spectrum biocontrol by Pseudomonas protegens CHA0 and other fluorescent pseudomonads is achieved through the generation of various secondary metabolites with antibiotic activities against not only other microbes but, also, nematodes and insects present in the rhizosphere. A previous metabolomic study demonstrated that intracellular low–molecular weight effectors, such as guanosine tetraphosphate and γ-aminobutyrate, function as important signals in niche adaptation by strain CHA0 to plant roots. We investigated the role of amino acids in the biocontrol trait of P. protegens Cab57 towards Pythium damping off and root rot in cucumber. Among the 11 amino acids tested, only glutamate markedly enhanced the efficacy of biocontrol. An RNA-Seq analysis revealed that glutamate upregulated the expression of a chitinase gene cluster (c21370-c21380, in which the c21370 gene was annotated as a gene encoding the chitin-binding protein cbp and the c21380 gene encoded chitinase chiC) in strain CHA0. Glutamate upregulated the expression of the regulatory small RNA rsmZ but reduced the production levels of other Gac/Rsm-regulated biocontrol factors, such as 2,4-diacetylphloroglucinol and pyoluteorin. The promoter activity of cbp and chitinase activity were characterized in detail; their activities were up-regulated in response to glutamate and their expression was under the control of GacA. Therefore, glutamate appears to be essential for biocontrol activity in which chitinase production is regulated in response to glutamate.

Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

保护假单胞菌CHA0 和其他荧光假单胞菌的广谱生物防治是通过产生各种具有抗生素活性的次生代谢产物来实现的，这些代谢物不仅针对其他微生物，而且还针对根际存在的线虫和昆虫。先前的代谢组学研究表明，细胞内低分子量效应子，例如四磷酸鸟苷和γ-氨基丁酸，在菌株 CHA0 对植物根部的生态位适应中发挥重要信号作用。我们研究了氨基酸在P. protegens Cab57 对黄瓜腐霉猝倒病和根腐病的生防性状中的作用。在测试的 11 种氨基酸中，只有谷氨酸显着增强了生物防治的功效。RNA-Seq分析显示，谷氨酸上调了菌株CHA0中几丁质酶基因簇（c21370-c21380，其中c21370基因注释为编码几丁质结合蛋白cbp的基因，c21380基因编码几丁质酶chiC）的表达。谷氨酸上调调节小RNA rsmZ的表达，但降低其他Gac/Rsm调节的生物防治因子的产生水平，例如2,4-二乙酰间苯三酚和脓毒素。对cbp启动子活性和几丁质酶活性进行了详细表征；它们的活性在谷氨酸的作用下上调，并且它们的表达受到 GacA 的控制。因此，谷氨酸似乎对于生物防治活动至关重要，其中几丁质酶的产生根据谷氨酸进行调节。

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