Inactivation of the GacA response regulator in Pseudomonas fluorescens Pf‐5 has far‐reaching transcriptomic consequences

Abstract

Summary The GacS/GacA signal transduction system is a central regulator in Pseudomonas spp., including the biological control strain P. fluorescens Pf‐5, in which GacS/GacA controls the production of secondary metabolites and exoenzymes that suppress plant pathogens. A whole genome oligonucleotide microarray was developed for Pf‐5 and used to assess the global transcriptomic consequences of a gacA mutation in P. fluorescens Pf‐5. In cultures at the transition from exponential to stationary growth phase, GacA significantly influenced transcript levels of 635 genes, representing more than 10% of the 6147 annotated genes in the Pf‐5 genome. Transcripts of genes involved in the production of hydrogen cyanide, the antibiotic pyoluteorin and the extracellular protease AprA were at a low level in the gacA mutant, whereas those functioning in siderophore production and other aspects of iron homeostasis were significantly higher in the gacA mutant than in wild‐type Pf‐5. Notable effects of gacA inactivation were also observed in the transcription of genes encoding components of a type VI secretion system and cytochrome c oxidase subunits. Two novel gene clusters expressed under the control of gacA were identified from transcriptome analysis, and we propose global‐regulator‐based genome mining as an approach to decipher the secondary metabolome of Pseudomonas spp.

Bibliographic Information