CONICET | Buscador de Institutos y Recursos Humanos

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 recently 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 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. We recently showed that blsA transcript and protein levels are lower at 37°C than at 24°C in cells obtained from motility plates [1], with the concomitant lack of photoregulation at high temperatures. Another point of control occurs on the functionality of the BlsA photocycle itself at different temperatures, which occurs with an average quantum yield of photoactivation of the signaling state of 0.20 _ 0.03 at 15°C < T < 25°C, but is practically inoperative at T > 30°C, as a result of 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 [2],.This allowed us to propose a model of integration of both light and temperature signals throught BlsA. To broaden our knowledge on the mechanisms of signal perception and transduction, we characterized in this work the events that take place at critical temperatures where photoregulation stops occurring, and also by means of both physiological as well as biophysical data. Our results using strain Acinetobacter baumannii ATCC 17978 show that critical temperature for motility photoregulation is 24ºC, implying that at 24ºC we observe inhibition of motility under blue light, while the bacteria move at 25ºC under the same conditions. We further characterized this effect by studying blsA transcript levels in cells obtained from motility plates at these temperatures through qRT-PCR. In particular, we focused in temperature changes from 23 through 26ºC, from 24 directly to 37ºC, and also in changes from light to dark or viceversa in the short scale of time at different temperatures. Our results indicate that blsA levels change in concert with the photoregulation phenotype, showing intermediate levels at in the short-time scale. Light conditions modulate global features related to persistence and virulence in the nosocomial pathogen Acinetobacter baumannii, and getting insights into the mechanism of light perception and transduction could contribute to broaden our understanding of this important behavior

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