Identification of a 3-Component Regulatory System that Regulates
Biofilm Maturation
and Virulence Gene Expression
We have identified
a 3-component regulatory system that controls biofilm maturation in P. aeruginosa.
The SadARS system has sequence similarity to the Bvg system of the pathogen Bordetella
pertussis. The organization of the region is shown to the right.
Mutations in this region do not have any apparent effect on biofilm formation in the flow cell system at early time periods (up to 2 days). However, by 5 days, while the WT makes a typical structure of large macrocolonies surrounded by open channels, the original transposon mutation (sad-160::Tn5) or constructed insertion/deletion strains result in a homogeneous biofilm lacking wide channels.
We used DNA microarrays to identify genes controlled by the SadARS system. We identified numerous genes controlled by this regulatory system. One set of genes controlled by SadARS in biofilm-grown cells, but not planktonic cells, are those genes required for the type III secretion system (TTSS). Interestingly, mutations in the TTSS of P. aeruginosa (i.e., pcrY and popB) enhanced biofilm formation. As shown below, adherence of these mutant strains to a plastic surface at the air-liquid interface (ALI) resulted in denser biofilms than those formed by the WT.
Our current model is based on the idea that bacteria may have a choice – cause a chronic infection (which requires the TTSS) or initiate a chronic, biofilm infection wherein virulence factors are down regulated. Based on the phenotype of the sadARS mutant, we believe this decision point comes downstream of microcolony formation, as illustrated below.
For more information about this work, please go to:
O'Toole GA. 2004. Microbiology: Jekyll or hide? Nature. 432:680-1