Insights into the mechanism of light and temperature perception through BlsA in Acinetobacter baumannii.

VALLE LORENA; ABATEDAGA INÉS; GOLIC A.E.; BORSARELLI C.; MÜLLER G.L.; M. A. MUSSI

Villa Carlos Paz, Cordoba

Congreso; XIII Encuentro Latinoamericano de Fotoquímica y Fotobiología (XIII ELAFOT); 2017

The ability of Acinetobacter baumannii to move is considered a pathogenicity factor given that it could contribute to bacterial persistence and dissemination in the nosocomial setting, in addition to biofilm formation and bacterial resistance to antimicrobial compounds. We have demonstrated that motility is modulated by light at 24ºC in this microorganism [1], resulting in inhibition of motility under blue light while the bacteria move throughout the plate in the dark. This bacterial response depends on the expression of the blue-light-sensing A (blsA) gene, which codes for a photoreceptor protein that contains an N-terminal blue-light-sensing-using flavin (BLUF) domain. Hence, the blsA transcript and protein levels were lower at 37°C than at 24°C in cells obtained from motility plates [1], with the concomitant lack of photoregulation at high temperatures. More recently, we extended the study of the BlsA photocycle as a function of temperature by spectroscopic characterization [2], demonstrating that between 15°C < T < 25°C the photoactivation to the signaling state sBlsA occurred with an average quantum yield of 0.20 ± 0.03, but it was practically inoperative at T > 30°C, due to conformational changes produced in the nanocavity of FAD. This effect would be important when the photoreceptor is already present in the cell to avoid almost instantaneously further signaling process when it is no longer necessary, for example under circumstances of temperature changes possibly faced by the bacteria, allowing us to propose a model of integration of both light and temperature signals through BlsA [2].To broaden our knowledge on the mechanism of signal perception and transduction in A. baumannii, in this work we have focused on the characterization of the transition from the photoregulation-proficient to the light-insensitive states observed in this organism, mediated by BlsA. Our results using strain ATCC 17978 show that the critical temperature for motility photoregulation is 24 (±0.06) ºC. In particular, we observe inhibition of motility at 23 and 24ºC under blue light, while the bacteria are able to move from 25 until 37ºC under the same illumination conditions. We further characterized this effect by studying blsA transcript levels in cells obtained from motility plates at these temperatures through qRT-PCR and found that blsA levels are important for adaptation to temperature changes, in addition to other more instantaneous mechanisms such as control of BlsA photoactivity. When the photocycle of BlsA protein was characterized by static and dynamic fluorescence spectroscopy at temperatures ranging from 14 to 37 (±0.1) ºC, we found a loss of the photocycling ability around 24-25ºC, since above this temperature fluorescence data indicated a loosening of the nanocavity of FAD.Hence, we demonstrate by the linking of physiological and biophysical data how evolution has chosen this combined light and temperature modulation to ensure the survival of this pathogen, also modulating global features related to persistence and virulence in the nosocomial pathogen Acinetobacter baumannii. Getting insights into the mechanism of light perception and transduction could contribute to broaden our understanding of this important behavior.[1] M. A. Mussi, J. A. Gaddy, M. Cabruja, B. A. Arivett, A. M. Viale, R. Rasia, L. A. Actis. The Opportunistic Human Pathogen Acinetobacter baumannii Senses and Responds to Light. J. Bacteriol. 2010, 192, p. 6336.[2] I. Abatedaga, L. Valle, A.E. Golic, G. Muller, M. Cabruja, F.E. Morán Vieyra, P.C. Jaime, M.A. Mussi , C.D. Borsarelli. Integration of temperature and blue light sensing in Acinetobacter baumannii through the BlsA sensor. Photochem. Photobiol. 2017, 93, 805-814.