Circadian rhythms in the critical human pathogen Acinetobacter baumannii

Abstract

Acinetobacter baumannii is recognized as the paradigm of multidrug resistant superbug, topping the WHO priority list of critical human pathogens. Interestingly, it senses and responds to blue light, which modulates global aspects of its physiology including the pathogenicity. We hypothesized that light could serve as a signal to synchronize the bacterial physiology to the host’s behavior, or to the environment. At environmental temperatures, light regulation is mainly governed by the BLUF-type photoreceptor BlsA. In this work, we identified the existence of daily rhythms in blsA expression displaying a robust response to light, as well as endogenous circadian rhythms in A. baumannii. In fact, we show that blsA gene expression can be synchronized to 24-hour blue light-dark cycles, which immediately resynchronizes after a phase shift due to a longer night. Upon release to constant darkness, bacterial populations present free-running oscillations with a period close to 24 hours. Furthermore, our data indicate that BlsA is involved in synchronization to the zeitgeber during light-dark cycles. Importantly, β-lactamase activity varied along the day in cultures under light-dark period, establishing a new paradigm. Our work contributes to the developing field of circadian clocks in bacterial human pathogens, which could impact the microorganisms’ lifestyle and pathogenicity.