AUTHOR=Zhang Qing Xia , Xiong Zheng Wen , Li Shen Yu , Yin Yue , Xing Cheng Lin , Wen De Yu , Xu Jian , Liu Qin 

TITLE=Regulatory roles of RpoS in the biosynthesis of antibiotics 2,4-diacetyphloroglucinol and pyoluteorin of Pseudomonas protegens FD6

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.993732

DOI=10.3389/fmicb.2022.993732

ISSN=1664-302X

ABSTRACT=<p>The rhizosphere microbe <italic>Pseudomonas protegens</italic> FD6 possesses beneficial traits such as the production of antibiotics like pyoluteorin (Plt) and 2,4-diacetylphloroglucinol (2,4-DAPG). The alternative RpoS (σ<sup>38</sup> factor), as a master regulator, activates or inhibits the transcription of stationary phase genes in several biocontrol organisms. Here, we investigated the complicated function and regulatory mechanism of RpoS in the biosynthesis of 2,4-DAPG and Plt in strain FD6. Phenotypic assays suggested that ΔrpoS was impaired in biofilm formation, swimming motility, swarming motility, and resistance to stress, such as heat, H<sub>2</sub>O<sub>2</sub> and 12% ethanol. The RpoS mutation significantly increased both 2,4-DAPG and Plt production and altered the transcription and translation of the biosynthetic genes <italic>phlA</italic> and <italic>pltL</italic>, indicating that RpoS inhibited antibiotic production by FD6 at both the transcriptional and translational levels. RpoS negatively controlled 2,4-DAPG biosynthesis and transcription of the 2,4-DAPG operon <italic>phlACBD</italic> by directly interacting with the promoter sequences of <italic>phlG</italic> and <italic>phlA.</italic> In addition, RpoS significantly inhibited Plt production and the expression of its operon <italic>pltLABCDEFG</italic> by directly binding to the promoter regions of <italic>pltR, pltL and pltF.</italic> Further analyzes demonstrated that a putative R147 mutation in the RpoS binding domain abolished its inhibitory activity on the expression of <italic>pltL</italic> and <italic>phlA</italic>. Overall, our results reveal the pleiotropic regulatory function of RpoS in <italic>P. protegens</italic> FD6 and provide the basis for improving antibiotic biosynthesis by genetic engineering in biocontrol organisms.</p>