How dormant bacterial spores process environmental cues

Despite being biochemically inactive, long dormant bacterial spores can process environmental cues over time by gradually releasing stored electrochemical potential to resume biological activity and growth at an appropriate time, researchers report. The findings reveal a cellular decision-making mechanism that operates in physiologically inactive cells. Sensing the onset of harsh environmental conditions, spore-forming organisms, including bacteria and fungi, can enter dormant states that can persist for years, even decades, until conditions become more favorable for germination. Although the dormant state of bacterial spores is generally thought to be devoid of biological activity, dormant spores retain the ability to process environmental cues that can signal release from dormancy. However, how physiologically inactive spores achieve this level of environmentally aware decision-making remains unknown. Using a mathematical model and experiments on thousands of Bacillus subtilis spores, Kaito Kikuchi and colleagues show that dormancy release may be explained by electrochemical-state switching, similar to that used by neurons. Similar to a decision-making mechanism in neurobiology known as “integrate-and-fire,” bacterial spores use an electrochemical potential caused by a gradient of potassium-ion (K⁺) concentrations across the dormant spore membrane to trigger germination. As spores are transiently and repeatedly exposed to environmental cues, more K⁺ are effluxed from the spore’s core to its inner membrane until a critical threshold is reached, switching the spore state from dormant to active. This mechanism allows environmental cues to be monitored over time without the need for energy production in the dormant spore. “Future work examining the germination behavior of spores originating from divergent taxa may provide useful insights into how environmental conditions dictate thresholds for germination,” write Jonathan Lombardino and Briana Burton in a related Perspective.