Gut microbiota as a key regulator of stress responsivity via the circadian system

The circadian system coordinates physiological and behavioral responses to environmental challenges across the day. Increasing evidence suggests that the gut microbiota may be an important component of this temporal regulation. The microbiome exhibits robust daily oscillations and communicates extensively with metabolic, neuroendocrine, and neural systems, creating opportunities for bidirectional interactions between microbial and host circadian rhythms. Recent work demonstrates that disruption of the gut microbiota alters circadian regulation of the hypothalamic-pituitary-adrenal axis, leading to changes in glucocorticoid rhythmicity and time-of-day-dependent alterations in stress responsivity. These findings highlight the microbiota as a potential regulator of how organisms adapt to environmental challenges at different times of day. Together with emerging work on microbiota-derived signals and circadian physiology, these findings support an expanding view of the gut microbiome as an integral component of the biological systems that coordinate physiology and behavior over time.