CONICET | Buscador de Institutos y Recursos Humanos

Acinetobacter baumannii has been recognized by the World Health Organization as one of the most threatening pathogens deserving urgent action. Key factors determining its success as pathogen include its extraordinary ability to develop resistance to antimicrobials as well as to persist in the hospital environment. Quorum sensing regulates bacterial population´s behavior in response to diverse environmental signals, modulating motility and biofilm formation in A. baumannii. The QS circuit of A. baumannii consists of the AbaI inducer and its cognate receptor AbaR. AbaI is a sensor that functions as an auto-inducer synthase producing homoserine lactones (HSL), while AbaR functions as a HSL receptor inducing a cascade leading ultimately to diverse cellular responses. On its side, the AidA enzyme is capable of hydrolysing the HSL molecules.We have extensively studied the response to light of these pathogens at environmental temperatures such as 23ºC, which depends on the BLUF photoreceptor BlsA. In this work, we show that light modulates the production of secreted molecules that modulate motility, since only the filtered supernatant of 17978 cells recovered from motility plates incubated in the dark, but not under blue light, were able to promote motility in the abaI mutant in the dark, which on its own is not able to move neither in the dark nor under blue light as is unable to synthesize HSL. In the presence of light, neither the filtered supernatant of 17978 cells obtained from motility plates incubated in the dark nor under blue light, was able to induce motility in the 17978 wild type or in the abaI mutant, suggesting the production of lactonase/s in this condition. The presence of lactonase/s in the wild type as well as in the abaI mutant supernatants only under blue light was further confirmed by motility assays supplemented with sonicated cellular extracts. qRT-PCR analyses showed, as expected, that the expression of abaI is modulated by light, being induced in the dark respect to light. These results support the above notion that HSL are produced in the dark and not under blue light in the wild type. The induction is dependent on BlsA, since photoregulation is lost in the blsA mutant. On its side, aidA expression is also photoregulated being induced in the presence of light, showing an inverse pattern than abaI, and dependency on BlsA. The modulation by light of the production of HSL in 17978 through BlsA was also confirmed by using the biological HSL sensor Chromobacterium violaceum. The overall data indicate that light modulates quorum sensing in A. baumannii.