Introduction: Circadian rhythm disruption is prevalent in modern society, particularly in night shift workers. Circadian misalignment - the misalignment between the central circadian clock and behavioral/environmental cycles (i.e., sleep/wake, fasting/feeding, dark/light) results in adverse metabolic effects. Potential underlying mechanisms for these adverse effects include alterations in the orogastrointestinal microbiota. However, it remains to be established whether human salivary microbiota have circadian rhythmicity and whether circadian disruption impacts circadian rhythms, bacterial diversity, community structure, and composition of the microbiota.