The GacS sensor kinase controls phenotypic reversion of small colony variants isolated from biofilms of Pseudomonas aeruginosa PA14.
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.
Davies
James A
JA
Department of Biological Sciences, University of Calgary, Calgary, AB, Canada.
Harrison
Joe J
JJ
Marques
Lyriam L R
LL
Foglia
Ginevra R
GR
Stremick
Carol A
CA
Storey
Douglas G
DG
Turner
Raymond J
RJ
Olson
Merle E
ME
Ceri
Howard
H
D015107:4-Butyrolactone / Q000031:analogs & derivatives / Q000096:biosynthesis; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018441:Biofilms / Q000187:drug effects / Q000254:growth & development*; D008826:Microbial Sensitivity Tests; D010641:Phenotype; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000201:enzymology / Q000472:pathogenicity / Q000502:physiology*; D014774:Virulence
D001426:Bacterial Proteins; C091100:GacA protein, Bacteria; C088386:homoserine lactone; D011494:Protein Kinases; D015107:4-Butyrolactone