Isolation and Taxonomic Identification of Cultivable Heterotrophic Bacteria from Deep Sediment of the Mariana Trench

To investigate the diversity of culturable heterotrophic bacteria in deep-sea sediments from the Mariana Trench, this study focused on a sediment core collected from the Challenger Deep at a depth of 10 816 meters on July, 2020. Samples from the surface and various depths within the sediment core were selected, and multiple enrichment and isolation techniques were employed to enhance the culturability of marine bacteria from extreme environments. Cultivation was performed at three temperatures (4, 16, and 28 ℃) using two solid media (MA and R2A) for direct plating, and three enrichment media (IMB, IMB-DMSP, and IMB-Rpf) for selective cultivation. A total of 517 strains of heterotrophic bacteria were obtained, and preliminary identification of potentially novel bacterial taxa was conducted based on 16S rRNA gene sequence comparisons. The results revealed that the isolated 517 strains belonged to 4 phyla (Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes), 8 classes, 30 orders, 42 families, 74 genera, and 144 species. Different enrichment strategies yielded distinct bacterial isolates, with the IMB-Rpf medium enabling the recovery of a broader diversity of microbial species. The addition of revival factors such as DMSP and supernatants from Mcrococcus luteus had selective enrichment effects on various culturable microbial populations in the sediments. Additionally, compositional differences in the cultured bacterial species were observed among different sediments depths. 51 strains from the 4 phyla represented potential new taxonomic units, including 3 potential new genera and 41 potential new species. Notably, 2 strains of them belonged to the class Sphingobacteriia, which have not previously been isolated from Mariana Trench sediments. The research results will provide a substantial resource of deep-sea bacterial strains for future scientific studies and offer new insights into the isolation and cultivation of microorganisms from extreme deep-sea environments.