1887

Abstract

The biocontrol agent F113 undergoes phenotypic variation during rhizosphere colonization, and this variation has been related to the activity of a site-specific recombinase encoded by the gene. Here, it is shown that a second recombinase encoded by the gene is also implicated in phenotypic variation. A putative gene from this strain was cloned, and sequence analysis confirmed that it encoded a site-specific recombinase of the integrase family. Mutants affected in the or genes produced a very low quantity of phenotypic variants compared to the wild-type strain, both under prolonged cultivation in the laboratory and after rhizosphere colonization, and they were severely impaired in competitive root colonization. Overexpression of the genes encoding either recombinase resulted in a substantial increment in the production of phenotypic variants under both culture and rhizosphere colonization conditions, implying that both site-specific recombinases are involved in phenotypic variation. Overexpression of the gene suppressed the phenotype of a mutant, but overexpression of the gene had no effect on the phenotype of an mutant. Genetic analysis of the phenotypic variants obtained after overexpression of the genes encoding both the recombinases showed that they carried mutations in the / genes, which are necessary to produce a variety of secondary metabolites. These results indicate that the Gac system is affected by the activity of the site-specific recombinases. Transcriptional fusions of the and genes with a promoterless gene showed that both genes have a similar expression pattern, with maximal expression during stationary phase. Although the expression of both genes was independent of diffusible compounds present in root exudates, it was induced by the plant, since bacteria attached to the root showed enhanced expression.

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2005-03-01
2019-11-21
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