The contribution of host tissue location and sex to epiphytic bacterial community assembly of Sargassum thunbergii

The formation of epiphytic bacterial communities on macroalgae is closely related to host identity, but the effects of tissue location and sex of the host alga on this process, especially the relative contributions of these two factors, have not been studied. Here, the epiphytic bacterial community on three different tissues (tip, receptacle and holdfast) of male and female Sargassum thunbergii in the intertidal zone of Qingdao was investigated using high-throughput sequencing, and the results revealed obvious tissue and sex specificity of the epiphytic bacteria and significant differences from seawater bacterial samples. The biodiversity indexes, specific bacteria, biomarkers, indicator taxa and predicted function of epiphytic bacteria differed significantly among tissues of S. thunbergii and between sexes for the same tissue, confirming that both algal tissue location and sex impacted epiphytic bacterial community assembly on S. thunbergii. Additionally, & beta;-diversity analysis showed that tissue location contributed more than host sex to epiphytic bacterial community structure, and the contributions of these two factors varied among tissues. Sex contributed less to epiphytic bacteria on the holdfast than on the tip and receptacle. Furthermore, the tissue and sex specificity of epiphytic bacteria on S. thunbergii were likely related mainly to host metabolism but also to the interaction between bacteria and algae and adaptability to the environment. This study shed light on the drivers of macroalga-associated bacterial community structure and broaden our understanding of the relationship between macroalgae and their epiphytic bacteria.