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Signalling by the fungus Pythium ultimum represses expression of two ribosomal RNA operons with key roles in the rhizosphere ecology of Pseudomonas fluorescens F113
Author(s) -
Smith Loraine M.,
Tola Elisabetta,
DeBoer Paulo,
O'gara Fergal
Publication year - 1999
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1046/j.1462-2920.1999.00067.x
Subject(s) - biology , pseudomonas fluorescens , operon , transposable element , pythium ultimum , mutant , gene , rhizosphere , reporter gene , genetics , northern blot , lac operon , ribosomal rna , gene expression , microbiology and biotechnology , botany , bacteria , rhizoctonia solani
Pseudomonas fluorescens F113 produces antifungal metabolites that protect the roots of sugarbeet from the fungus Pythium ultimum . The phytopathogen, in turn, has the ability to downregulate the expression of genes fundamental to the rhizosphere competence of the bacterial strain. This paper describes the characterization of two of these genes, which were isolated by screening a mini‐Tn 5 :: lacZ mutant bank for differential expression of β‐galactosidase in the presence of P. ultimum . In order to identify the genes affected in reporter mutants SF3 and SF5, the transposons and flanking regions were cloned. Sequence analysis of the regions flanking the transposons in SF3 revealed that mini‐Tn 5 :: lacZ had inserted into a tRNA Ile gene, which maps within a ribosomal RNA ( rrn ) operon. In SF5, the transposon inserted between the promoter of a second rrn operon and a gene encoding a 16S rRNA. Southern blot analysis demonstrated that there are five rrn operons in P. fluorescens F113 and that the transposons in SF3 and SF5 had inserted into two different operons. Further characterization of these mutants suggests that their reduced rhizosphere competence is not the result of reduced viability in the short term but may be accounted for partly by reduced growth rates under conditions that support rapid growth. Analysis of lacZ expression in the reporter mutants indicate that the marked rrn operons are regulated differently, suggesting different physiological roles.