Sarniguet A, Kraus J, Henkels M D, Muehlchen A M, Loper J E
Institut National de la Recherche Agronomique, Centre de Recherches de Rennes, Le Rheu, France.
Proc Natl Acad Sci U S A. 1995 Dec 19;92(26):12255-9. doi: 10.1073/pnas.92.26.12255.
Pseudomonas fluorescens Pf-5, a rhizosphere-inhabiting 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 sigma s. 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-diacetyl-phloroglucinol, 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 sigma 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.
荧光假单胞菌Pf-5是一种栖居于根际的细菌，可抑制多种植物土传病原菌，它能产生抗生素吡咯菌素、绿脓菌素和2,4-二乙酰基间苯三酚。Pf-5产生吡咯菌素所必需的一个基因被鉴定为rpoS，它编码稳定期σ因子σs。在Pf-5的RpoS-突变体中也观察到了大肠杆菌中rpoS突变的几种多效性效应。这些效应包括稳定期细胞对过氧化氢或高盐浓度所施加压力的敏感性。含有克隆的野生型rpoS基因的质粒恢复了Pf-5的RpoS-突变体的吡咯菌素产生和胁迫耐受性。RpoS-突变体过量产生绿脓菌素和2,4-二乙酰基间苯三酚，这两种抗生素可抑制植物病原真菌终极腐霉的生长，并在抑制终极腐霉引起的黄瓜幼苗猝倒方面优于野生型。当以高细胞密度接种到黄瓜种子上时，RpoS-突变体在发育中的幼苗表面的存活情况不如野生型菌株。Pf-5的其他稳定期特异性表型，如氰化物和细胞外蛋白酶的产生，在RpoS-突变体中也有表达，这表明σs只是荧光假单胞菌稳定期细胞中基因转录所需的σ因子之一。这些结果表明rpoS编码的σ因子影响荧光假单胞菌在植物表面的抗生素产生、生物防治活性和存活。
