Abstract: Upwelling promotes material cycling and energy flow in offshore ecosystems through enhanced diffusion and unique environmental driving, which directly affects the growth, reproduction, and distribution of organisms in the environment. There are a large number of uncultivated and difficult to cultivate microorganisms and new gene resources. In this study, 27 seawater samples were collected from the surface, middle and bottom layers of the upwelling area in eastern Guangdong to explore the diversity and distribution patterns of bacteria and their correlation with depth. A total of 1928 bacterial strains were isolated by pure culture method, and identified by 16S rRNA gene sequence, the results showed that these bacteria were distributed in 5 phyla, 9 classes, 32 orders, 54 families, 121 genera and 262 species. Among them, Proteobacteria was the dominant phylum, accounting for 46.9%. Actinomycetia was the dominant class, accounting for 44.8%. Microbacteriales was the dominant order, accounting for 21.2%. In general, the diversity of strains isolated from the mid-level seawater was significantly lower than that from the surface and bottom seawater environments, but the dominant populations obtained from the three levels of seawater environments were basically the same, and the most optimal group was Microbacteriales. The number of potential new bacteria isolated from different water layers was ranked as bottom layer > surface layer > middle layer. The rate of potential new bacteria isolated from different media was ranked as follows: 2216E medium >R2A medium >ISP2 medium >MSM medium >IMK medium. Canonical Correspondence Analysis (CCA) of bacterial diversity and environmental factors showed that The environmental factors that significantly affected the changes of diversity were chlorophyll content (Chl), reactive silicate (ASS), reactive phosphate (AP), ammonia and some amino acids (Amm), and biochemical oxygen demand (BOD). In this study, we systematically investigated the diversity and distribution of culturable Marine microorganisms in the upwelling area of eastern Guangdong. The results accumulated key microbial information and data for the study of culturable bacterial diversity in different water layers in the offshore upwelling area, and also provided reference for the exploration and utilization of species and gene resources in the typical offshore upwelling environment.

Key words: East Guangdong upwelling, culturable bacterial diversity, different isolation medium, different water layers