Influences of the diurnal cycle on gut microbiota in the Chinese swamp shrimp (Neocaridina denticulata)

ABSTRACT The circadian rhythm is an essential environmental factor affecting several physiological activities in organisms, including crustaceans. However, daily variations in the gut bacterial community composition of crustaceans remain poorly understood. This study aimed to elucidate variations in the gut bacterial community composition of the Chinese swamp shrimp Neocaridina denticulata with the diurnal cycle. The gut samples of 600 shrimps were collected at four time points (6:00, 12:00, 18:00, and 24:00) within a 24 h period and 16S rRNA high-throughput gene sequencing was applied. The alpha-diversity and richness of the gut bacterial community were highest in the 24:00 group. Food digestion- and absorption-related pathways were highly enriched, indicating that metabolic process pathways are influenced by the daily cycle. Opportunistic pathogenic bacteria, including Flavobacterium, Acinetobacter, and Pseudomonas, were well-represented in the 18:00 and 24:00 groups, suggesting that the daily cycle shapes pathogenic bacterial community composition in the shrimp intestine. Our findings provide new insights into the role of diurnal cycles on gut bacteria in crustaceans and may aid in improving N. denticulata aquaculture.