The GacS sensor kinase controls phenotypic reversion of small colony variants isolated from biofilms of Pseudomonas aeruginosa PA14

• Published in: FEMS microbiology ecology Vol. 59; no. 1; pp. 32 - 46
• Main Authors: Davies, James A., Harrison, Joe J., Marques, Lyriam L. R., Foglia, Ginevra R., Stremick, Carol A., Storey, Douglas G., Turner, Raymond J., Olson, Merle E., Ceri, Howard
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.01.2007; Blackwell; Oxford University Press
• Subjects: 4-Butyrolactone - analogs & derivatives; 4-Butyrolactone - biosynthesis; Amikacin; Antibiotics; Antiinfectives and antibacterials; Antimicrobial agents; Antimicrobial resistance; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; biofilm; Biofilms; Biofilms - drug effects; Biofilms - growth & development; Biological and medical sciences; Cations; Cell culture; Cell density; Colonies; Complementation; Drug resistance; Ecology; Fundamental and applied biological sciences. Psychology; Histidine; Histidine kinase; Hydrogen peroxide; Kinases; Lactones; Microbial Sensitivity Tests; Microbiology; Miscellaneous; Morphology; Mutation; Pathogens; Phenotype; Phenotypic reversion; Piperacillin; Protein Kinases - genetics; Protein Kinases - metabolism; Pseudomonas aeruginosa; Pseudomonas aeruginosa - drug effects; Pseudomonas aeruginosa - enzymology; Pseudomonas aeruginosa - pathogenicity; Pseudomonas aeruginosa - physiology; quorum sensing; Reversion; Rifampin; small colony variant; two‐component signal transduction; Virulence; quorum sensing; two-component signal transduction; antimicrobial resistance; biofilm; small colony variant; Pseudomonadales; Amikacin; Virulence; Antimicrobial agent; Regulation(control); Reversion; Histidine; Gene; Bacteria; Pseudomonadaceae; Pseudomonas aeruginosa; Serum; Antituberculous agent; Peroxides; Human; Enzyme; Transferases; Metabolism; Hydrogen Peroxides; Strain; two- component signal transduction; Resistance; Kinase; Biofilm; Cations; Mutation; Antibacterial agent; antimicrobia resistance
• ISSN: 0168-6496; 1574-6941
• DOI: 10.1111/j.1574-6941.2006.00196.x

Abstract The GacS/GacA two-component regulatory system in pseudomonads regulates genes involved in virulence, secondary metabolism and biofilm formation. Despite these regulatory functions, some Pseudomonas species are prone to spontaneous inactivating mutations in gacA and gacS. A gacS− strain of Pseudomonas aeruginosa PA14 was constructed to study the physiological role of this sensor histidine kinase. This loss-of-function mutation was associated with hypermotility, reduced production of acylhomoserine lactones, impaired biofilm maturation, and decreased antimicrobial resistance. Biofilms of the gacS− mutant gave rise to phenotypically stable small colony variants (SCVs) with increasing frequency when exposed to silver cations, hydrogen peroxide, human serum, or certain antibiotics (tobramicin, amikacin, azetronam, ceftrioxone, oxacilin, piperacillin or rifampicin). When cultured, the SCV produced thicker biofilms with greater cell density and greater antimicrobial resistance than did the wild-type or parental gacS− strains. Similar to other colony morphology variants described in the literature, this SCV was less motile than the wild-type strain and autoaggregated in broth culture. Complementation with gacS in trans restored the ability of the SCV to revert to a normal colony morphotype. These findings indicate that mutation of gacS is associated with the occurrence of stress-resistant SCV cells in P. aeruginosa biofilms and suggests that in some instances GacS may be necessary for reversion of these variants to a wild-type state.