Submitted to: Acta Horticulturae
Publication Type: Abstract Only
Publication Acceptance Date: 3/3/1999
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: We evaluated the role of the global regulatory gene rpoS in stress response of two biological control agents, the rhizosphere bacterium Pseudomonas fluorescens Pf-5 and P. fluorescens A506. The rpoS gene encodes for a protein (RpoS) that mediates coordinated expression of phenotypes expressed by stationary phase cells. An rpoS mutant of Pf-5 did not produce the secondary metabolite pyrrolnitrin; exhibited decreased tolerance to oxidative, freezing, and starvation stresses imposed in the laboratory; and established lower population sizes than wild-type Pf-5 in the rhizosphere of bean, particularly when planted in dry soil. Stock cultures of A506 had a frame-shift mutation in rpoS that resulted in the production of a non-functional, truncated RpoS protein. We repaired the frame-shift mutation, and the repaired rpoS produced a full-length, functional RpoS protein. A506 was more sensitive to starvation than was a derivative strain with the repaired rpoS; but the responses of these strains to other stresses imposed in the laboratory were similar. Under field conditions, A506 and the RpoS+ derivative strain established similar population sizes on pear blossoms. The importance of expression of attributes associated with stationary phase cells and the influence of rpoS on fitness of P. fluorescens on plant tissues was strain-dependant.