Discovery of an Antibiotic-Related Small Protein of Biocontrol Strain Pseudomonas sp. Os17 by a Genome-Mining Strategy.

Kasumi Takeuchi,Kosumi Yamada,Wataru Tsuchiya,Zui Fujimoto,Nobutaka Someya,Toshimasa Yamazaki

doi:10.3389/fmicb.2020.605705

Abstract

Many root-colonizing Pseudomonas spp. exhibiting biocontrol activities produce a wide range of secondary metabolites that exert antibiotic effects against other microbes, nematodes, and insects in the rhizosphere. The expression of these secondary metabolites depends on the Gac/Rsm signal transduction pathway. Based on the findings of a previous genomic study on newly isolated biocontrol pseudomonad strains, we herein investigated the novel gene cluster OS3, which consists of four genes (Os1348–Os1351) that are located upstream of putative efflux transporter genes (Os1352–Os1355). Os1348 was predicted to encode an 85-aa small precursor protein, the expression of which was under the control of GacA, and an X-ray structural analysis suggested that the Os1348 protein formed a dimer. The mutational loss of the Os1348 gene decreased the antibiotic activity of Pseudomonas sp. Os17 without changing its growth rate. The Os1349–1351 genes were predicted to be involved in post-translational modifications. Intracellular levels of the Os1348 protein in the deficient mutant of each gene differed from that in wild-type cells. These results suggest that Os1348 is involved in antibiotic activity and that the structure or expression of this protein is under the control of downstream gene products.

Highlights

Root-colonizing fluorescent pseudomonads are known to be plant-beneficial strains that suppress the growth of other microbes, including plant pathogens, nematodes, and insects
Pseudomonas protegens strains CHA0 and Pf-5 have been used as model strains in research on the biosynthesis and regulation of secondary metabolites by these pseudomonads
We demonstrated that the function of the well-known Gac/Rsm signal transduction pathway (Lapouge et al, 2008; Kidarsa et al, 2013; Valentini and Filloux, 2016) was conserved in Os17, in which the production of rhizoxin analogs was under the control of GacA (Takeuchi et al, 2015)

Summary

INTRODUCTION

Root-colonizing fluorescent pseudomonads are known to be plant-beneficial strains that suppress the growth of other microbes, including plant pathogens, nematodes, and insects Strains in this group have the potential to produce various secondary metabolites and enzymes with antibiotic activities, which enable them to compete with other microbes, thereby facilitating niche adaptation in the rhizosphere. Comparative genomics among closely related strains revealed phenotype-specific genes, thereby enabling us to identify strainspecific biocontrol factor(s). In addition to these strain-specific gene clusters, clusters commonly shared by the genomes of Os17 and St29, but absent from the genomes of P. protegens, are of interest because they may contribute to establishing the uniqueness of this putative novel species. We demonstrated that the downstream genes of Os1348 affected the protein status of Os1348

MATERIALS AND METHODS

RESULTS

DISCUSSION

DATA AVAILABILITY STATEMENT