Glutamate Positively Regulates Chitinase Activity and the Biocontrol Efficacy of Pseudomonas protegens

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 gamma-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 bio-control. An RNA-Seq analysis revealed that glutamate upregu-lated 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 chiti-nase chiC) in strain CHA0. Glutamate upregulated the expres-sion of the regulatory small RNA rsmZ but reduced the pro-duction levels of other Gac/Rsm-regulated biocontrol factors, such as 2,4-diacetylphloroglucinol and pyoluteorin. The pro -moter activity of cbp and chitinase activity were characterized in detail; their activities were up-regulated in response to glu-tamate and their expression was under the control of GacA. Therefore, glutamate appears to be essential for biocontrol ac-tivity in which chitinase production is regulated in response to glutamate.

Automated summary

Glutamate enhances the biocontrol activity of Pseudomonas protegens Cab57 against Pythium damping off and root rot in cucumber by upregulating the expression of a chitinase gene cluster. The production levels of other biocontrol factors are reduced by glutamate. Glutamate plays an essential role in biocontrol activity where chitinase production is regulated.