Communications biologyOct 1, 2025

The human pathogen Acinetobacter baumannii shows daily rhythms controlled by light

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗OA ↗

Updated Jun 27, 2026

Abstract

Essence

Acinetobacter baumannii showed light-synchronized and free-running rhythms close to 24 hours, implicating in circadian-like timing.

Evidence

This bacterial physiology experiment measured blsA promoter activity and rhythmic behavior under 24-hour blue light-dark cycles, phase shifts, and constant darkness, including BlsA-related comparisons.

Caveat

The work demonstrates rhythms in bacterial populations under experimental light conditions but does not test direct effects on infection, host behavior, or pathogenicity.

Simplified

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 pathogenicity. We hypothesized that light could serve as a signal to synchronize the bacterial physiology to the host's behavior and/or to the environment. At environmental temperatures, light regulation is mainly governed by the photoreceptor . In this work, we identified the existence of daily rhythms in blsA promoter activity displaying a robust response to light, as well as endogenous in A. baumannii. In fact, we show that blsA promoter activity can be synchronized to 24-hour blue light-dark cycles, which immediately resynchronizes after a phase shift. 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 light-dark cycles. In fact, under constant darkness without previous entrainment, A. baumannii is rhythmic, but acrophases are not clusterized, behaving as the blsA mutant under light-dark cycles. Our work contributes to the developing field of circadian clocks in bacterial pathogens, which could impact in the microorganisms' lifestyle and pathogenicity.