Involvement of SOS response and c-di-GMP signaling in biofilm formation of pseudomonas aeruginosa via DNA and protein release
Biofilm formation by Pseudomonas aeruginosa, an opportunistic human pathogen, is associated with high rates of illness and death in patients with cystic fibrosis, with immunecompromised states, with burn and wound infections. Exposure to antimicrobial therapy is likely to stimulate biofilm formation. Biofilm stimulation by such agents as DNA replication inhibitors might be launched via sophisticated mechanisms: the inhibitors trigger the bacterial SOS response to repair DNA damage while biofilm formation involves a signaling pathway via bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP). The signaling pathway has profound effects on bacterial physiology while the SOS response generates genetic instability. Pathogens under these influences may evolve, and unexpected traits, such as protective biofilms, may emerge. Our central hypothesis is that in response to replication inhibition, P. aeruginosa biofilm formation is controlled by SOS through Arr, and the biofilms serve as a rehabilitation center for cells with replication damage. This hypothesis is essentially grounded on our studies that P. aeruginosa under replication inhibition tends to form biofilms via Arr, a c-di-GMP phosphodiesterase that degrades c-di-GMP. In this study, fact that the SOS response is involved in the stimulation of biofilm was confirmed by the reduced biofilm in RecA mutant, in comparison to wild type and RecA complimentary strain, and the observations of Z-stack readings made by the confocal laser scanning microscopy. The DNA and protein release are SOS controlled is confirmed by the increase in the DNA and protein release in the presence of replication inhibitors at different time points. The protein release with biofilm stimulation is noted by the increase in the biofilm by the SOS mutant RecA in the presence of the wild type proteins. The involvement of the Arr was observed by the protein profiles of the wild type and Arr mutant. The rehabilitation of the bacteria in biofilm cells is noticed by the observation of the lanes in pulsed field gel electrophoresis with 8hr biofilm and 24hr biofilm cells in which the DNA damage is reduced in case of 24hrs samples.