New Insights into the Diurnal Rhythmicity of Gut Microbiota and Its Crosstalk with Host Circadian Rhythm

SIMPLE SUMMARY: There is a growing consensus that the gut microbiota exhibits diurnal oscillation. The rhythmicity of gut microbiota has fundamental implications for host physiology, metabolism, and health. Further, the gut microbiota rhythmicity can regulate the host’s circadian rhythm. Therefore, in this review, we aimed to highlight the rhythmic phenomenon of the gut microbiota and elucidate its fundamental roles in host physiology, metabolism, and health, and illuminate the possible interactions between the gut microbiota rhythmicity and host circadian rhythm. Insights into these questions facilitate the development of chronotherapy. ABSTRACT: Unlike the strictly hierarchical organization in the circadian clock system, the gut microbiota rhythmicity has a more complex multilayer network of all taxonomic levels of microbial taxa and their metabolites. However, it is worth noting that the functionality of the gut microbiota rhythmicity is highly dependent on the host circadian clock and host physiological status. Here, we discussed the diurnal rhythmicity of the gut microbiota; its crucial role in host physiology, health, and metabolism; and the crosstalk between the gut microbial rhythmicity and host circadian rhythm. This knowledge lays the foundation for the development of chronotherapies targeting the gut microbiota. However, the formation mechanism, its beneficial effects on the host of gut microbial rhythmicity, and the dynamic microbial–host crosstalk are not yet clear and warrant further research.