The Pathogen Acinetobacter Baumannii uses Light as a Signal for the Regulation of Virulence

Acinetobacter baumannii is a human bacterial pathogen with pronounced morbidity and mortality rates in immunocompromised patients. With the prominent rise of multidrug-resistant strains, understanding the mechanisms by which this bacterium regulates its virulence is imperative for the development of alternative treatments and prevention. Our laboratory has previously showed that one such environmental signal to which A. baumannii responds is light.

     Earlier, we had determined that the photoreceptor BlsA is primarily responsible for light-mediated regulation at 24ºC; BlsA regulates a myriad of virulence factors including iron-uptake, motility, and acetoin metabolism. Through the Beckman funds, we were able to broaden BlsA’s sphere of influence to include A. baumannii’s response to oxidative stress, specifically through differential regulation of catalase and superoxide dismutase activities. Additionally, we showed that specific amino acid residues of the C-terminal region of BlsA are critical for this regulation and interaction with protein partners that effect light-mediated regulatory responses. Ultimately, these findings further characterized the overall structural mechanisms of BlsA that allow light-mediated regulation in A. baumannii at 24ºC, a temperature that reflects the nosocomial environment.

     Notably, we have also found that light regulation occurs at the human-host relevant temperature of 37ºC, a condition at which BlsA no longer functions as an active photoreceptor. In particular, we have shown upregulation of the conjugation of a plasmid conferring multidrug-resistance under darkness. This finding has led us to further clarify the importance of this plasmid for A. baumannii virulence, with primary focus on peroxide resistance, motility, and macrophage uptake of bacteria. 

     Overall, our findings provide a more global insight into how A. baumannii is able to use light as a signal to confer virulence both in and outside of the host.