Affiliation:
1. Département de Microbiologie Fondamentale, Université de Lausanne, CH-1015 Lausanne
2. Phytopathology Group, Institute of Plant Sciences, Swiss Federal Institute of Technology, CH-8092 Zürich, Switzerland
Abstract
ABSTRACT
In the biocontrol strain
Pseudomonas fluorescens
CHA0, the Gac/Rsm signal transduction pathway positively controls the synthesis of antifungal secondary metabolites and exoenzymes. In this way, the GacS/GacA two-component system determines the expression of three small regulatory RNAs (RsmX, RsmY, and RsmZ) in a process activated by the strain's own signal molecules, which are not related to
N
-acyl-homoserine lactones. Transposon Tn
5
was used to isolate
P. fluorescens
CHA0 insertion mutants that expressed an
rsmZ-gfp
fusion at reduced levels. Five of these mutants were
gacS
negative, and in them the
gacS
mutation could be complemented for exoproduct and signal synthesis by the
gacS
wild-type allele. Furthermore, two thiamine-auxotrophic (
thiC
) mutants that exhibited decreased signal synthesis in the presence of 5 × 10
−8
M thiamine were found. Under these conditions, a
thiC
mutant grew normally but showed reduced expression of the three small RNAs, the exoprotease AprA, and the antibiotic 2,4-diacetylphloroglucinol. In a gnotobiotic system, a
thiC
mutant was impaired for biological control of
Pythium ultimum
on cress. Addition of excess exogenous thiamine restored all deficiencies of the mutant. Thus, thiamine appears to be an important factor in the expression of biological control by
P. fluorescens
.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
22 articles.
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