Articles
INFLUENCE OF RPOS ON COLONIZATION OF PEAR BLOSSOMS BY THE BACTERIAL ANTAGONIST PSEUDOMONAS FLUORESCENS A506
Article number
489_115
Pages
647 – 648
Language
Abstract
Establishment of populations of bacterial antagonists on blossoms is an important step in biological control of fire blight.
Bacterial cells unable to tolerate environmental stresses encountered on blossoms are unlikely to persist in the field.
The global regulator gene rpoS encodes for a protein (RpoS) that mediates coordinated expression of phenotypes associated with stationary phase cells (i.e. production of secondary metabolites and tolerance to environmental stresses). An RpoS mutant of the rhizosphere inhabitant Pseudomonas fluorescens strain 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 field soils.
Stock cultures of A506 had a frame-shift mutation in rpoS that resulted in the production of a truncated RpoS. The rpoS containing the frame-shift mutation isolated from A506 did not complement an RpoS mutant of Pf-5. We repaired the frame-shift mutation in rpoS in A506 with PCR. The repaired rpoS produced a full-length transcript of RpoS and complemented an RpoS mutant of Pf-5. A506, a derivative of A506 with an nptl-insertion in rpoS (RpoS–), and an isolate with a repaired rpoS (RpoS+), were similar in their tolerance to several stresses imposed in laboratory assays, except the RpoS+ isolate maintained significantly higher population sizes than the other strains under conditions of starvation.
Under field conditions, A506 established similar population sizes on pear blossoms as the RpoS– and RpoS+ derivatives.
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.
Bacterial cells unable to tolerate environmental stresses encountered on blossoms are unlikely to persist in the field.
The global regulator gene rpoS encodes for a protein (RpoS) that mediates coordinated expression of phenotypes associated with stationary phase cells (i.e. production of secondary metabolites and tolerance to environmental stresses). An RpoS mutant of the rhizosphere inhabitant Pseudomonas fluorescens strain 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 field soils.
Stock cultures of A506 had a frame-shift mutation in rpoS that resulted in the production of a truncated RpoS. The rpoS containing the frame-shift mutation isolated from A506 did not complement an RpoS mutant of Pf-5. We repaired the frame-shift mutation in rpoS in A506 with PCR. The repaired rpoS produced a full-length transcript of RpoS and complemented an RpoS mutant of Pf-5. A506, a derivative of A506 with an nptl-insertion in rpoS (RpoS–), and an isolate with a repaired rpoS (RpoS+), were similar in their tolerance to several stresses imposed in laboratory assays, except the RpoS+ isolate maintained significantly higher population sizes than the other strains under conditions of starvation.
Under field conditions, A506 established similar population sizes on pear blossoms as the RpoS– and RpoS+ derivatives.
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.
Publication
Authors
V.O. Stockwell, M.J. Hagen, C.A. Whistler, J.E. Loper
Keywords
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