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

ADRIAN GOLIC; LORENA VALLE; GABRIELA MÜLLER; CLAUDIO D. BORSARELLI; INES ABATEDAGA; MARIA ALEJANDRA MUSSI

Villa Carlos Paz, Cordoba, Argentina

Conferencia; XIII ELAFOT 2017; 2017

The ability of Acinetobacter baumannii to move is considered a pathogenicity factor given that itcould contribute to bacterial persistence and dissemination in the nosocomial setting, in addition tobiofilm formation and bacterial resistance to antimicrobial compounds. We have demonstrated thatmotility is modulated by light at 24ºC in this microorganism [1], resulting in inhibition of motilityunder blue light while the bacteria move throughout the plate in the dark. This bacterial responsedepends on the expression the blue-light- sensing A (blsA) gene, which codes for a photoreceptorprotein that contains an N-terminal blue-light- sensing-using flavin (BLUF) domain. Hence, the blsAtranscript 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 extendedthe 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 occuredwith an average quantum yield of 0.20  0.03, but it was practically inoperative at T > 30°C, due toconformational changes produced in the nanocavity of FAD. This effect would be important when thephotoreceptor is already present in the cell to avoid almost instantaneously further signaling processwhen it is no longer necessary, for example under circumstances of temperature changes possiblyfaced by the bacteria, allowing us to propose a model of integration of both light and temperaturesignals 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 thephotoregulation-proficient to the light-insensitive states observe in this organism, mediated by BlsA.Our results using strain ATCC 17978 show that the critical temperature for motility photoregulation is24ºC. In particular, we observed inhibition of motility at 23 and 24ºC under blue light, while thebacteria were able to move from 25 until 37ºC under the same illumination conditions. We furthercharacterized this effect by studying blsA transcript levels in cells obtained from motility plates atthese temperatures through qRT-PCR. In particular, we focused in temperature changes from 23through 26 ºC, and our preliminary results show a sequential reduction in blsA levels under blue lightas temperature increases. We also studied blsA levels when temperature shifted from 24 to 37ºC in ashort physiological time scale, and observed a decrease in blsA levels progressively with time,reaching a minimun at 60 min. This provides an indication that control of blsA levels are important foradaptation to temperature changes, in addition to other more instantaneous mechanisms such ascontrol of BlsA photoactivity. To further characterize the transition, we studied the bacterial motilityin plates subjected to cyclic temperature changes from 24 to 37ºC, with a 6 hs-duration each period.Our results indicate that temperature changes from 24 to 37 and viceversa are reversible and thebacteria are able to perceive and regulate motility according to each condition, despite at differentgrowth phases we observed differential speed in adaptation.Light conditions modulate global features related to persistence and virulence in the nosocomialpathogen Acinetobacter baumannii, and getting insights into the mechanism of light perception andtransduction 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 OpportunisticHuman Pathogen Acinetobacter baumannii Senses and Responds to Light. Journal of Bacteriology, Dec. 2010,Vol 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 ,Borsarelli C.D. (2017). Integration of temperature and blue light sensing in Acinetobacter baumannii throughthe BlsA sensor. Photochem. Photobiol. 93, 805-814.