title: Regulation of GacA in Pseudomonas chlororaphis Strains Shows a Niche Specificity.
abstract: The GacS/GacA two-component system plays a central role in the regulation of a broad range of biological functions in many bacteria. In the biocontrol organism Pseudomonas chlororaphis, the Gac system has been shown to positively control quorum sensing, biofilm formation, and phenazine production, but has an overall negative impact on motility. These studies have been performed with strains originated from the rhizosphere predominantly. To investigate the level of conservation between the GacA regulation of biocontrol-related traits in P. chlororaphis isolates from different habitats, the studies presented here focused on the endophytic isolate G5 of P. chlororaphis subsp. aurantiaca. A gacA mutant deficient in the production of N-acylhomoserine lactones (AHLs) and phenazine was isolated through transposon mutagenesis. Further phenotypic characterization revealed that in strain G5, similar to other P. chlororaphis strains, a gacA mutation caused inability to produce biocontrol factors such as phenazine, HCN and proteases responsible for antifungal activity, but overproduced siderophores. LC-MS/MS analysis revealed that AHL production was also practically abolished in this mutant. However, the wild type exhibited an extremely diverse AHL pattern which has never been identified in P. chlororaphis. In contrast to other isolates of this organism, GacA in strain G5 was shown to negatively regulate biofilm formation and oxidative stress response whilst positively regulating cell motility and biosynthesis of indole-3-acetic acid (IAA). To gain a better understanding of the overall impact of GacA in G5, a comparative proteomic analysis was performed revealing that, in addition to some of the traits like phenazine mentioned above, GacA also negatively regulated lipopolysaccharide (LPS) and trehalose biosynthesis whilst having a positive impact on energy metabolism, an effect not previously described in P. chlororaphis. Consequently, GacA regulation shows a differential strain dependency which is likely to be in line with their niche of origin.
authors.affiliation: School of Food and Biological Engineering, Jiangsu University, Zhenjiang, 212013, China; Institute of Life Sciences, Jiangsu University, Zhenjiang, 212013, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.affiliation: Institute of Life Sciences, Jiangsu University, Zhenjiang, 212013, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.affiliation: School of Life Sciences, Centre for Biomolecular Sciences, University of Nottingham, Nottingham, NG7 2RD, United Kingdom.
authors.forename: Jean-Frédéric
authors.initials: JF
authors.lastname: Dubern
authors.affiliation: Department of Plant Pathology, Shandong Agricultural University, Taian, 271018, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: School of Life Sciences, Centre for Biomolecular Sciences, University of Nottingham, Nottingham, NG7 2RD, United Kingdom.
authors.forename: Nigel
authors.initials: N
authors.lastname: Halliday
authors.affiliation: Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, 76100, Israel.
authors.forename: Leonid
authors.initials: L
authors.lastname: Chernin
authors.affiliation: Department of Plant Pathology, Shandong Agricultural University, Taian, 271018, China.
authors.forename: Kexiang
authors.initials: K
authors.lastname: Gao
authors.affiliation: School of Life Sciences, Centre for Biomolecular Sciences, University of Nottingham, Nottingham, NG7 2RD, United Kingdom.
authors.forename: Miguel
authors.initials: M
authors.lastname: Cámara
authors.affiliation: Institute of Life Sciences, Jiangsu University, Zhenjiang, 212013, China.
authors.forename: Xiaoguang
authors.initials: X
authors.lastname: Liu
mesh_terms: D054742:Acyl-Butyrolactones / Q000378:metabolism*; D000935:Antifungal Agents / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics*; D018441:Biofilms / Q000254:growth & development; D002465:Cell Movement / Q000235:genetics; D004734:Energy Metabolism / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D006856:Hydrogen Cyanide / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism; D008070:Lipopolysaccharides / Q000096:biosynthesis; D018384:Oxidative Stress / Q000235:genetics; D010619:Phenazines / Q000378:metabolism*; D040901:Proteomics; D011549:Pseudomonas / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D053038:Quorum Sensing / Q000235:genetics; D053719:Tandem Mass Spectrometry; D014199:Trehalose / Q000096:biosynthesis
chemical_list: D054742:Acyl-Butyrolactones; D000935:Antifungal Agents; D001426:Bacterial Proteins; C091100:GacA protein, Bacteria; D007210:Indoleacetic Acids; D008070:Lipopolysaccharides; D010619:Phenazines; C000598831:phenazine; D006856:Hydrogen Cyanide; C030737:indoleacetic acid; D014199:Trehalose