The Gac regulon of Pseudomonas fluorescens SBW25

Abstract

Transcriptome analysis of Pseudomonas fluorescens SBW25 showed that 702 genes were differentially regulated in a gacS::Tn5 mutant, with 300 and 402 genes up- and downregulated respectively. Similar to the Gac regulon of other Pseudomonas species, genes involved in motility, biofilm formation, siderophore biosynthesis and oxidative stress were differentially regulated in the gacS mutant of SBW25. Our analysis also revealed, for the first time, that transcription of 19 rhizosphere-induced genes and of genes involved in type II secretion, (exo)polysaccharide and pectate lyase biosynthesis, twitching motility and an orphan non-ribosomal peptide synthetase (NRPS) were significantly affected in the gacS mutant. Furthermore, the gacS mutant inhibited growth of oomycete, fungal and bacterial pathogens significantly more than wild type SBW25. Since RP-HPLC analysis did not reveal any potential candidate metabolites, we focused on the Gac-regulated orphan NRPS gene cluster that was predicted to encode an eight-amino-acid ornicorrugatin-like peptide. Site-directed mutagenesis indicated that the encoded peptide is not involved in the enhanced antimicrobial activity of the gacS mutant but may function as a siderophore. Collectively, this genome-wide analysis revealed that a mutation in the GacS/A two-component regulatory system causes major transcriptional changes in SBW25 and significantly enhances its antimicrobial activities by yet unknown mechanisms.

The Gac/Rsm Signaling Pathway of a Biocontrol Bacterium, Pseudomonas chlororaphis O6

“…For example, production of pyoverdine-like siderophores and indole acetic acid (IAA) from tryptophan (Kang et al, 2006) are increased in a PcO6 gacS mutant. This control of siderophore production by Gac/Rsm was not restricted to PcO6, but were observed similar repressive effects of Gac on siderophore production in P. fluorescens Pf-5 (Hassan et al, 2010) and P. fluorescens SBW25 (Cheng et al, 2013).…”

“…The Gac/Rsm regulon is far-reaching, controlling expression of the about 10% genes of the genome in P. fluorescens Pf-5, P. fluorescens SBW25, and Pc30-84 (Cheng et al, 2013;Hassan et al, 2010;Wang et al, 2013). The Gac/Rsm regulon includes expression of alternative sigma factors, each of which has its own regulatory network (Fig.…”

The Global Response Regulator ExpA Controls Virulence Gene Expression through RsmA-Mediated and RsmA-Independent Pathways in Pectobacterium wasabiae SCC3193

“…Some of the larger operons of significantly downregulated virulence-related genes in the expA mutant were involved in the general secretion pathway (gspSBCDEFGHIJKLMO operon, W5S_1291 to W5S_1305), the type VI secretion system (T6SS) cluster called T6SS-1 in SCC3193 (3), the T6SS-related hcp and vgrG genes, and PCWDE production. Many of these alterations in gene expression were similar to those found in gacA mutants of Pseudomonas species (11,34,46,51,52). When more relaxed significance cutoff values (a P value of Յ0.005 instead of an FDR of Յ0.05) were used, the downregulation of genes involved in flagellar biosynthesis (fliRQPONMLKJIHGF, W5S_1790 to W5S_ 1802) and phosphonate metabolism (phnGHIJKLMNP, W5S_ 0593 to W5S_0601) was apparent as well in the expA mutant, particularly during stationary growth (see Data Set S4 in the supplemental material).…”

The Two-Component Regulators GacS and GacA Positively Regulate a Nonfluorescent Siderophore through the Gac/Rsm Signaling Cascade in High-Siderophore-Yielding Pseudomonas sp. Strain HYS

“…In Pseudomonas fluorescens and Pseudomonas chlororaphis, a defect in gacS-gacA causes increased production of siderophores, including pyoverdine and pyochelin (25)(26)(27)(28), together with an increase in the expression of siderophore-related genes, as shown by transcriptome analysis of P. fluorescens (28,29). In contrast, gacA mutants of Pseudomonas aeruginosa M18 and Pseudomonas marginalis exhibit reduced pyoverdine production (30,31).…”