Submitted to: Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2005
Publication Date: 10/1/2005
Citation: Stockwell, V.O., Loper, J.E. 2005. The sigma factor rpos is required for stress tolerance and environmental fitness of pseudomonas fluorescens pf-5. Microbiology. 151:3001-3009. Interpretive Summary: This research is part of an ongoing program to identify factors that influence the success of biological control for management of plant diseases. Growers need reliable biological control agents that they can depend upon to manage plant diseases in agriculture, so our research is focused on identifying factors that influence the effectiveness of biological control agents. In this manuscript, we describe the influence of a global regulatory gene, rpoS, on the biological control agent Pseudomonas fluorescens Pf-5. We show that this gene influences the capacity of Pf-5 to colonize seed and root surfaces in an agricultural field. We also show that rpoS is required for Pf-5 to survive exposure to UV light, freezing temperatures, desiccation, and starvation, all of which are likely to occur on surfaces of plants in the field. This research is important as one component in a larger program to identify sources of variation in biological control, thereby working towards the development of more reliable biologically-based management programs for agriculture.
Technical Abstract: Many microorganisms exist in natural habitats that are subject to severe or dramatically fluctuating environmental conditions. Such is the case for bacteria inhabiting plant surfaces where they are exposed to UV irradiation, oxygen radicals, and large fluctuations in temperature and moisture. This study focuses on the role of RpoS, a central regulator of stationary-phase gene expression in bacterial cells, in stress response and environmental fitness of Pseudomonas fluorescens Pf-5. Strain Pf-5 is a rhizosphere-inhabiting bacterium that suppresses plant diseases caused by several plant pathogenic fungi and Oomycetes. Previous studies demonstrated that rpoS was required for osmotic and oxidative stress resistance of Pf-5. The results of this study demonstrate a role for rpoS in tolerance of Pf-5 to freezing, starvation, UV irradiation, and desiccation stress. In field studies, an rpoS mutant was compromised in rhizosphere colonization of plants in dry soil, whereas similar rhizosphere populations were established by Pf-5 and an rpoS mutant in well-irrigated soils. RpoS is a key determinant in stress response and environmental fitness of the rhizosphere bacterium P. fluorescens Pf-5.