Abstract:[Background] Most marine microorganisms are uncultivated. In order to excavate the culturable microbial resources in the marine ecosystem, we tried some methods, such as oligotrophic culture. [Objective] To compare the differences in bacterial population, community structure and utilization characteristics of carbon sources of South China Sea under different low-nutrient culture conditions. [Methods] The seawater samples from South China Sea were cultured in the original 2216E medium (group Y), diluted 10 times (group Y-10) and 50 times (group Y-50) in 2216E culture medium. The number of bacteria and the structure of bacterial communities were detected by real-time PCR and 16S rRNA gene. The number of heterotrophic bacteria was also counted by plate counting method, and the culturable bacteria were separated and identified. The utilization characteristics of carbon sources of bacterial communities in different media were analyzed by Biolog EcoPlateTM method. [Results] The total number of bacteria in Y group was higher than that in Y-10 group and Y-50 group (P>0.05), but the number of heterotrophic bacteria was significantly higher than that in Y-10 group and Y-50 group (P<0.05). The sequencing of 16S rRNA gene shows that the bacterial community structure was significantly different under different dilution multiples, in the Y group, 10 phyla and 193 genera were detected, and the dominant groups were Proteobacteria (56.44%) and Bacteroides (37.27%); in the Y-10 group, 15 phyla and 220 genera were detected, and the dominant groups were Proteobacteria (40.30%), Bacteroides (36.91%) and Firmicutes (17.30%); in the Y-50 group, 14 phyla and 226 genera were detected, and the dominant groups were Proteobacteria (45.19%), Bacteroides (25.29%), Planctomycetes (13.58%) and Firmicutes (11.21%). Through plate culture, 14 dominant bacteria of 6 genera were isolated from Y group and Y-10 group, 13 dominant bacteria of 7 genera were isolated from Y-50 group. Among them, Bacillus is the common dominant bacteria. Four dominant bacteria (1 strain of Microbacterium, 1 strain of Vibro, 1 strain of Idiomarina, 1 strain of Halobacillus) screened by diluting 10 times of culture medium and nine dominant bacteria (1 strain of Alcanivorax, 1 strain of Sulfitobacter, 1 strain of Alteromonas, 1 strain of Pseudomonas, 2 strains of Exiguobacterium, 3 strains of Vibro) screened by diluting 50 times of culture medium were different from the original culture medium. Through low-nutrient culture, the metabolic activity and McIntosh index of culturable bacterial communities increased significantly (P<0.05), and its utilization rate of polymers, carboxylic acids, amino acids and carbohydrates also increased significantly (P<0.05). [Conclusion] Low-nutrient culture can increase the richness and diversity of bacterial community, improve the metabolic activity of culturable bacteria and the utilization of carbon sources, especially polymers, carboxylic acids, amino acids and carbohydrates. Therefore, in the collection and recovery of culturable bacteria samples in the pelagic area of South China Sea, more abundant culturable microbial resources can be obtained through low-nutrient culture method.
