The gut microbial of sea urchin ( <i>Strongylocentrotus intermedius</i> ) under different temperatures: Microbial structure and co-occurrence patterns

The gut bacterial community plays a vital role in adjusting host adaptation to temperature variation, a key factor influencing physiology. Currently, the effects of temperature on the bacterial community of sea urchins remain unknown. In this study, the structural alterations and community reassembly of the gut bacterial community in sea urchins ( Strongylocentrotus intermedius ) under different temperatures (13 ℃, 16 ℃, 19 ℃, 22 ℃, and 25 ℃) were investigated by high-throughput sequencing. After 30 days of exposure, high temperatures increase bacterial diversity and alter the structure of the bacterial community. Proteobacteria, Bacteroidota, and Firmicutes were the dominant bacterial communities of S. intermedius , accounting for more than 80% of the total relative abundance. At 13 ℃, 16 ℃, and 19 ℃, Desulforhopalus , Cohaesibacter , and Pseudomonas were the dominant genera, with relative abundances of 34.25%, 11.71%, and 31.49%, respectively, whereas Ruegeria (30.21%) and Sphingomonas (33.23%) became dominant at 22 ℃ and 25 ℃. Functional prediction based on the KEGG database indicated that key metabolic pathways, including amino acid, carbohydrate, energy, and lipid metabolism, exhibited significant alterations across the different temperatures (P &lt; 0.05). Co-occurrence network analysis revealed that gut bacterial community network complexity was higher at 13 °C and 25 °C than at other temperatures, with the 13 °C and 25 °C groups exhibiting the greatest number of nodes (99) and edges (824). In addition, temperature fluctuations strengthened the deterministic assembly of the gut bacterial community, increased the host’s selective effect on gut bacteria, and reduced stochasticity. This study aims to provide some theoretical basis for the temperature effects of the gut bacterial community in the sea urchin.