Md. Parkins et al., Pseudomonas aeruginosa GacA, a factor in multihost virulence, is also essential for biofilm formation, MOL MICROB, 40(5), 2001, pp. 1215-1226
We have investigated a potential role for GacA, the response regulator of t
he GacA/GacS two-component regulatory system, in Pseudomonas aeruginosa bio
film formation. When gacA was disrupted in strain PA14, a 10-fold reduction
in biofilm formation capacity resulted relative to wild-type PA14. However
, no significant difference was observed in the planktonic growth rate of P
A14 gacA(-). Providing gacA in trans on the multicopy vector pUCP-gacA abro
gated the biofilm formation defect. Scanning electron microscopy of biofilm
s formed by PA14 gacA(-) revealed diffuse clusters of cells that failed to
aggregate into microcolonies, implying a deficit in biofilm development or
surface translocation. Motility assays revealed no decrease in PA14 gacA(-)
twitching or swimming abilities, indicating that the defect in biofilm for
mation is independent of flagellar-mediated attachment and solid surface tr
anslocation by pili. Autoinducer and alginate bioassays were performed simi
larly, and no difference in production levels was observed, indicating that
this is not merely an upstream effect on either quorum sensing or alginate
production. Antibiotic susceptibility profiling demonstrated that PA14 gac
A(-) biofilms have moderately decreased resistance to a range of antibiotic
s relative to PA14 wild type. This study establishes GacA as a new and inde
pendent regulatory element in P. aeruginosa biofilm formation.