The sigma factor sigma s affects antibiotic production and biological control activity of Pseudomonas fluorescens Pf-5.

Abstract

Pseudomonas fluorescens Pf-5, a rhizosphereinhabiting bacterium that suppresses several soilborne pathogens of plants, produces the antibiotics pyrrolnitrin, pyoluteorin, and 2,4-diacetylphloroglucinol. A gene necessary for pyrrolnitrin production by Pf-5 was identified as rpoS, which encodes the stationary-phase sigma factor as. Several pleiotropic effects of an rpoS mutation in Escherichia coli also were observed in an RpoS-mutant of Pf-5. These included sensitivities of stationary-phase cells to stresses imposed by hydrogen peroxide or high salt concentration. A plasmid containing the cloned wild-type rpoS gene restored pyrrolnitrin production and stress tolerance to the RpoS-mutant of Pf-5. The RpoS-mutant overproduced pyoluteorin and 2,4-diacetylphloroglucinol, two antibiotics that inhibit growth of the phytopathogenic fungus Pythium ultimum, and was superior to the wild type in suppression of seedling damping-off of cucumber caused by Pythium ultimum. When inoculated onto cucumber seed at high cell densities, the RpoS-mutant did not survive as well as the wild-type strain on surfaces of developing seedlings. Other stationary-phase-specific phenotypes of Pf-5, such as the production of cyanide and extracellular protease(s) were expressed by the RpoS-mutant, suggesting that a-s is only one of the sigma factors required for the transcription of genes in stationary-phase cells of P. fluorescens. These results indicate that a sigma factor encoded by rpoS influences antibiotic production, biological control activity, and survival of P. fluorescens on plant surfaces.

Regulatory roles of psrA and rpoS in phenazine-1-carboxamide synthesis by Pseudomonas chlororaphis PCL1391

“…1). A role of rpoS in antibiotic production has been reported (Sarniguet et al, 1995;Suh et al, 1999), but not for regulating PCN production. The inhibitory effect of RpoS on quorum sensing and pyocyanin in P. aeruginosa (Whiteley et al, 2000) or of PsrA and RpoS on quorum sensing in P. putida WCS358 (Bertani & Venturi, 2004) is the opposite of what we observed for strain PCL1391.…”

“…However, the results are different depending on the species and the antibiotic considered. For example, an rpoS mutation results in a decrease of pyrrolnitrin production by P. fluorescens, but in an increase of pyoluteorin and 2,4-diacetylphloroglucinol production by the same strain (Sarniguet et al, 1995) and of pyocyanin in P. aeruginosa (Suh et al, 1999). …”

“…rpoS encodes the stationary-phase alternative sigma factor s s , which is responsible for the switch in gene expression occurring upon exposure of cells to starvation and/ or various stresses (Lange & Hengge-Aronis, 1991). In Pseudomonas species, rpoS mutants are often affected in their secondary metabolism, and particularly in their antibiotic production (Sarniguet et al, 1995;Suh et al, 1999). However, the results are different depending on the species and the antibiotic considered.…”

Differential regulation of phenazine biosynthesis by RpeA and RpeB in Pseudomonas chlororaphis 30-84

“…Plasmid pJEL5649 containing rpoS from P. fluorescens Pf-5 (Sarniguet et al, 1995) was labelled with digitoxin according to the manufacturers' instructions (Boehringer Mannheim). Five cosmids were identified in the 30-84 genomic library that contained chromosomal DNA with homology to the rpoS probe.…”

A proteomic study of Methylobacterium extorquens reveals a response regulator essential for epiphytic growth

“…S is a master regulator of the general stress response in bacteria that belong to Gammaproteobacteria (43). Mutants deficient in S are less able to survive upon starvation and are more sensitive to oxidative and osmotic stress as well as UV and desiccation stress in both logarithmic-and stationary-phase cells in Enterobacteriaceae and pseudomonads (44)(45)(46). In Bacillus, B has been postulated to be the functional homologue of S .…”