BlsA is a low to moderate temperature blue light photoreceptor in the human pathogen Acinetobacter baumannii

ADRIAN GOLIC; LORENA VALLE; CLARISA E. ALVAREZ; CLARISA PARODI; PAULA C. JAIME; CLAUDIO D. BORSARELLI; INES ABATEDAGA; MARIA ALEJANDRA MUSSI

Frontiers in microbiology

Frontiers

Lugar: Laussane; Año: 2019

Light is an environmental signal that produces extensive effects on the physiology ofthe human pathogen Acinetobacter baumannii. Many of the bacterial responses tolight depend on BlsA, a blue-light- using FAD (BLUF)-type photoreceptor, which alsointegrates temperature signals. In this work, we disclose novel mechanistic aspectsof the function of BlsA. First, we show that light modulation of motility occurs only attemperatures lower than 24C, a phenotype depending on BlsA. Second, blsA transcriptlevels were significantly reduced at temperatures higher than 25C, in agreement withBlsA protein levels in the cell which were undetectable at 26C and higher temperatures.Also, quantum yield of photo-activation of BlsA (lBlsA) between 14 and 37C, showedthat BlsA photoactivity is greatly compromised at 25C and absent above 28C.Fluorescence emission and anisotropy of the cofactor together with the intrinsic proteinfluorescence studies suggest that the FAD binding site is more susceptible to structuralchanges caused by increments in temperature than other parts of the protein. Moreover,BlsA itself gains structural instability and aggregates aggressively at temperatures above30C. Overall, BlsA is a low to moderate temperature photoreceptor, whose functioningis highly regulated in the cell, with control points at expression of the cognate gene aswell as photoactivity.