Seasonal effects on bacterial community between intestine of Collichthys lucidus and water environment from Pearl River Estuary

Collichthys lucidus is a common dominant and economically important fish species in the Pearl River Estuary. To reveal the ecological characteristics of C. lucidus, we applied high-throughput sequencing technology of 16S rRNA gene to investigate the effects of seasonal changes on the bacterial community structure in the intestines and water body of the Pearl River Estuary. The bacterial community in the fish intestines was predominantly composed of members of Proteobacteria (78.89%), followed by Firmicutes (6.70%) and Bacteroidota (5.45%), while Proteobacteria (40.32%) and Bacteroidota (37.97%) dominated the surrounding water. Besides, we observed the seasonal changes in the dominant bacterial genera in the intestine of C. lucidus. The relative abundance of Psychrobacter was significantly higher in spring and summer, whereas Photobacterium predominated in autumn. However, Pseudomonas, Sva0996 marine group, Vibrio and Methylobacterium were more abundant in winter. The α-diversity index values of the intestinal bacteria of C. lucidus were highest in winter but lowest in autumn. PCoA and ANOSIM analyses reveal no significant differences in the intestinal bacterial composition between spring and summer (p>0.05), whereas significant differences were observed in the other seasons (p<0.05). The seasonal changes in the bacterial composition of surrounding water were similar to those in the fish intestinal bacteria. Mantel test analysis finds out that five bacterial genera (Tenacibaculum, Psychrobacter, Candidatus_Actinomarina, Salinimonas, OM60NOR5_clade) in water environment showed a significantly positive correlation with the intestinal bacteria of C. lucidus (r>0.4, p<0.01). Bacterial co-occurrence network analysis shows that the proportion of shared bacterial communities between the fish intestines and the water environment was lowest in winter but highest in summer. The results indicate that seasonal changes can impact both the intestinal bacterial communities of C. lucidus from the Pearl River Estuary and bacterial communities in water body.