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J. Bacteriol., Aug 1995, 4658-4668, Vol 177, No. 16
SI Grewal, B Han and K Johnstone
Pseudomonas tolaasii, the causal agent of brown blotch disease of Agaricus
bisporus, spontaneously gives rise to morphologically distinct stable
sectors, referred to as the phenotypic variant form, at the margins of the
wild-type colonies. The phenotypic variant form is nonpathogenic and
differs from the wild type in a range of biochemical and physiological
characteristics. A genomic cosmid clone (pSISG29) from a wild-type P.
tolaasii library was shown to be capable of restoring a range of
characteristics of the phenotypic variant to those of the wild-type form,
when present in trans. Subcloning and saturation mutagenesis analysis with
Tn5lacZ localized a 3.0-kb region from pSISG29, designated the pheN locus,
required for complementation of the phenotypic variant to the wild-type
form. Marker exchange of the Tn5lacZ-mutagenized copy of the pheN locus
into the wild-type strain demonstrated that a functional copy of the pheN
gene is required to maintain the wild-type pathogenic phenotype and that
loss of the pheN gene or its function results in conversion of the
wild-type form to the phenotypic variant form. The pheN locus contained a
2,727-bp open reading frame encoding an 83-kDa protein. The predicted amino
acid sequence of the PheN protein showed homology to the sensor and
regulator domains of the conserved family of two component bacterial sensor
regulator proteins. Southern hybridization analysis of pheN genes from the
wild type and the phenotypic variant form revealed that DNA rearrangement
occurs within the pheN locus during phenotypic variation. Analysis of pheN
expression with a pheN::lacZ fusion demonstrated that expression is
regulated by environmental factors. These results are related to a model
for control for phenotypic variation in P. tolaasii.
Copyright © 1995, American Society for Microbiology
Identification and characterization of a locus which regulates multiple functions in Pseudomonas tolaasii, the cause of brown blotch disease of Agaricus bisporus
Department of Plant Sciences, University of Cambridge, United Kingdom.
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