Light signal transduction through the global regulator BlsA, a BLUF-type photoreceptor from the human pathogen Acinetobacter baumannii

M. A. MUSSI

Barcelona

Congreso; 17th International Congress on Photobiology & 18th Congress of the European Society for Photobiology; 2019

European Society for Photobiology and

Light exerts a global effect on the physiology of the important human pathogen Acinetobacter baumannii at moderate temperatures, likely modulating the microorganism' persistence in the environment. Persistence in the clinical settings is a key aspect determining A. baumannii success as a pathogen. We have shown that light modulates biofilm formation, motility and virulence against Candida albicans. Light also modulates metabolic pathways including trehalose biosynthesis, a disaccharide likely involved in resistance to diseccation, and the phenylacetic acid degradation pathway. Light enhances antioxidant enzyme levels such as catalase, and modulates susceptibility and tolerance to some antibiotics. In addition, light induces the expression of whole gene clusters and pathways, including one involved in lipid modification, the complete type VI secretion system (T6SS) and efflux pumps. Many of these processes are controlled by a short Blue Light Using Flavin (BLUF) protein, BlsA, the only canonical photoreceptor codified in the genome of A. baumannii. We have disclosed the light signal transduction mechanism mediated by this photoreceptor by showing that BlsA binds to and antagonizes the functioning of the transcriptional repressor Fur only in the dark at 23ºC, likely by reducing its ability to bind to Acinetobactin promoters, with enhanced gene expression of the corresponding genes and growth under iron deprivation at this condition. Recently, we have broadened our understanding of BlsA functioning by showing that this photoreceptor can antagonize the functioning of other transcriptional regulators also under blue light such as the acetoin repressor AcoN. Indeed, BlsA interacts with AcoN only under blue light but not in the dark at 23 °C. Moreover, the acetoin catabolic genes acoA, acoB and acoC were induced at this condition in a BlsA and AcoN-dependent manner. Consistently, growth on acetoin was supported under blue light rather than in the dark through BlsA and AcoN. The data support a model in which BlsA interacts with and likely sequesters the acetoin repressor in the presence of light, relieving acetoin catabolic genes from repression and leading to much better growth at this condition. The phenomena depend on temperature, consistently with recent findings indicating BlsA functioning only at low-moderate temperatures. Overall, the global regulator BlsA can function both under blue light and in the dark modulating different transcriptional regulators simultaneously at moderate temperatures, leading to regulation of different sets of genes and cellular processes. BlsA probes to be unique regarding its dual activity under illumination and in the dark.