Entrainment of the Circadian Clock of the Enteric Bacterium <i>Klebsiella aerogenes</i> by Temperature Cycles

Abstract

We have previously shown that the gastrointestinal bacterium, Klebsiella (nee Enterobacter) aerogenes, expresses an endogenously generated and temperature-compensated circadian rhythm in swarming motility and gene expression. As a human gastrointestinal commensal, we hypothesized that this circadian rhythm may be synchronized/entrained in vivo by the daily rhythm in body temperature (TB). Cultures of K. aerogenes transformed to express a plasmid containing luxCDABE with a MotA promoter exhibited rhythms in bioluminescence and in spatial distribution on the culture dish with a circadian period (τ). To determine entrainment, cultures were exposed to temperature cycles of 1o (35oC-36oC) or 3oC (34oC-37oC) in amplitude and cycles with varying periods (T cycles) of T=22 hours, T=24 hours, or T=28 hours. Bacteria entrained to all 3 T cycles at both temperature amplitudes with stable phase relationships (Ψ) to the Zeitgebers. To better understand the nature of this entrainment, a phase response curve (PRC) was constructed in response to 1 hr. pulses of 3oC increase in temperature (34oC-37oC) at different circadian phases (Φ) of the bioluminescence rhythm. A very high amplitude PRC, with small phase shifts (ΔΦ) during subjective day, large phase delays (-ΔΦ) during early subjective night, and large phase advances (+ΔΦ) during late subjective night was constructed, explaining the entrainment patterns of these bacteria. A phase transition curve (PTC) revealed a Type 0 PRC. To determine whether spatial patterns of bioluminescence rhythms contributed to the overall circadian organization of K. aerogenes, cultures were imaged for 2.5 days in a cooled CCD camera system, revealing a spatiotemporal pattern the circadian rhythmicity. These data are consistent with the hypothesis that the K. aerogenes circadian clock entrains to its host via detection of and phase-shifting to the daily pattern of TB.