THE INTESTINAL MICROBIOME OF SEA CUCUMBER APOSTICHOPUS JAPONICUS DURING THE AESTIVATION PERIOD

Sea cucumber Apostichopus japonicus is an economically important marine echinoderm in China. The optimal temperature for feeding and growth of A. japonicus is around 14—16℃, while it enters an aestivation state when the temperature exceeds 25℃. Among marine invertebrates, A. japonicus has emerged as a suitable model organism for investigating aestivation induced by environmental factors, primarily due to increased temperature. The studies on elucidating the aestivation mechanism A. japonicus is increasing in recent years, which focused on physiology, metabolism, gene expression, and epigenetic regulation. The intestinal microbiota plays an essential role in the growth, development, and immune regulation of the host, while the knowledge regarding the succession of intestinal microbial community in A. japonicus during the aestivation period is still unclear. In this study, sea cucumbers with an average weight of (54.39±2.94) g were collected and acclimated for two weeks in a recirculating aquaculture system at 15℃. After acclimation, a total of 300sea cucumbers were randomly allocated into 10 tanks with five replicates of non-aestivation group (NAT) and aestivation group (AT). In the NAT group, the temperature was maintained at 15℃, while in the AT group, the water temperature increased from 15℃ to 26℃. The aestivation period lasted for one month, then the temperature decreased from 26℃ to 16—17℃ until the AT group recovered and began feeding activities. Seven times were collected according the temperature in the AT group, including after acclimation (1 time, labeled NAT0 and AT0), during aestivation (five times, NAT1-5 and AT1-5), and arousal from aestivation (1 time, labeled NAT6 and AT6). The intestinal microbial communities were investigated using high-throughput sequencing. The results showed that a total of 11552 ASVs, with only 14.57% shared between the NAT and AT groups. The intestinal and richness of microbial diversity were assessed using the Shannon and Chao 1 indices, showing distinct temporal dynamics both in the NAT and AT groups. The richness and diversity in AT1 and AT2samples were significantly lower than that in AT0 (P<0.05). The NMDS analysis based on Bray-Curtis distances showed that samples in the NAT and AT groups clustered separately, with significant differences confirmed by Anosim analysis. Proteobacteria, Bacteroidota, Firmicutes, Verrucomicrobiota, Actinobacteriota and Campylobacterota were the dominant phyla, with relative abundances ranging from 90.01% to 99.80%. The composition of the dominant genera differed significantly during the aestivation period. LEfSe analysis identified 9 biomarkers, including 7 of NAT and 2 of AT. Co-occurrence network analysis revealed that the NAT group had a more complex network structure than that of AT. The neutral model analysis (NCM) revealed that both NAT and AT microbial communities were predominantly influenced by deterministic processes. These findings provide valuable insights into the mechanisms of sea cucumber aestivation and offer a theoretical basis for the healthy breeding of A. japonicus in summer.