Exploring the diversity of cultivated bacteria in the Western Pacific waters through improved culture media

Abstract:

[Objective] The complex marine environment of the Western Pacific has unique ecosystems and biological communities, and contains abundant marine microbial resources. The community structure of bacteria in different water depths in the Western Pacific was studied based on isolation culture technique. We tried to improve the capturability of marine bacteria by modifying the culture medium. [Methods] We used five different culture media in this study: improved 2216E agar medium (IMA), R2A agar medium (R2A), MBM agar medium (MBM), thiosulfate citrate bile salts sucrose agar medium (TCBS) and improved 2216E liquid enriched medium (IMB). Through strain isolation and 16S rRNA gene sequence identification, the community structure and diversity of culturable bacteria from the surface layer to 6000 meters water depth of the Western Pacific were analyzed. We compared the similarities and differences of bacterial diversity in different culture media. [Results] In this study, we isolated and identified 1293 strains in total, which affiliated to four phyla, seven classes, 14 orders, 26 families, 52 genera and 119 species. Proteobacteria were the dominant group recovered from the seawaters. At the class level, γ-Proteobacteria, α-Proteobacteria, and Actinobacteria_c were the dominant microflora. The most dominant phyla obtained from the five cultures were all Proteobacteria, and the most dominant class was γ-Proteobacteria. Except for the TCBS in which the dominant order was Vibrionales, the most dominant order in other four media was Alteromonadales. In addition, the five media exhibited different selectivity at each taxonomic level. The diversity of the cultivable bacteria in the five culture media from high to low was R2A, IMA, MBM, TCBS and IMB. The most unique genera (up to 10) were isolated from R2A. With the increase of water depth, the number of cultivable heterotrophic microorganisms showed a decreasing trend. A total of 68 strains were potential new bacteria among all the isolates, and the rates of new bacteria were relatively high among IMA, R2A and MBM. [Conclusion] In this study, cultivable bacteria from the seawater of the Western Pacific were studied by using five different culture media, showing a high diversity and revealing the selectivity of different media for cultivable marine bacteria. This research has provided valuable microbial resources for other ecological and molecular studies, and it has also brought more inspiration for using improved culture medium to isolate uncultured marine microorganisms in the future.