SOS involvement in stress-inducible biofilm formation

Abstract

Bacterial biofilm formation can be induced by antimicrobial and DNA damage agents. These agents trigger the SOS response, in which SOS sensor RecA stimulates auto-cleavage of repressor LexA. These observations lead to a hypothesis of a connection between stress-inducible biofilm formation and the RecA-LexA interplay. To test this hypothesis, three biofilm assays were conducted, viz. the standard 96-well assay, confocal laser scanning microscopy, and the newly developed biofilm-on-paper assay. It was found that biofilm stimulation by the DNA replication inhibitor hydroxyurea was dependent on RecA and appeared repressed by the non-cleavable LexA of Pseudomonas aeruginosa. Surprisingly, deletion of lexA led to reduction of both normal and stress-inducible biofilm formation, suggesting that the wild-type LexA contributes to biofilm formation. The decreases was not the result of poor growth of the mutants. These results suggest SOS involvement in hydroxyurea-inducible biofilm formation. In addition, with the paper biofilm assay, it was found that degradation of the biofilm matrix DNA by DNase I appeared to render the biofilms susceptible to the replication inhibitor. The puzzling questions concerning the roles of LexA in DNA release in the biofilm context are discussed.

Keywords:

• Pseudomonas aeruginosa
• bacterial biofilm
• DNA replication inhibitor
• DNA damage
• recombination
• SOS response

Acknowledgements

The authors thank Dr Pradeep K. Singh for the recA strains, Dr Mark D. Sutton for the lexA strains, and Dr Floyd E. Romesberg for the LexA non-cleavable strain. They also thank Dr Colleen Witt and Ms Yan Wu for CLSM at UTSA RCMI, Drs James Chambers and Luke Duam for assisting with setting up the laboratory, Drs Jilani Chaudry and Richard G. LeBaron and Ms M. M. Navarro for kind technical support, Reshma Maredia and Ruby Gonzalez for assistance with the paper biofilm assays, and Ms Maria Macias and Aijie Liu for laboratory maintenance. Finally, they are grateful to the US Air Force at Brooks City Base in San Antonio for kind support of facilities. This work was supported by the start-up fund provided by the University of Texas at San Antonio, an Entrepreneur Initiative Grant from Brooks Air Force Base in San Antonio, and the San Antonio Area Foundation.