Abundance and Molecular Diversity of Thraustochytrids in Coastal Waters of Southern China

Abstract

Thraustochytrids are unicellular fungi-like (heterotrophic) marine protists and have long been considered to play an important role in the biogeochemical cycles of the coastal oceans. However, the significance of their ecological functions and diversity in marine ecosystems remain largely unknown. In this report, we examined the spatial and temporal variations of planktonic thraustochytrids, their relationship with other environmental factors, and their diversity in the subtropical coastal waters of China. The abundance of planktonic thraustochytrids ranged from 2.56 × 10⁵ to 17.57 × 10⁵ cells L⁻¹ with highest abundance detected in polluted coastal water and the Spring (March) season. Thraustochytrids biomass was greater than bacterial biomass in most of seawater samples, ranging from 32.29 to 359.51% that of bacterioplankton. The abundance of thraustochytrids appeared to be largely related to that of bacterioplankton and chemical oxygen demand (COD) in water columns. High-throughput sequencing analyses revealed a total of 105 OTUs (97% similarity), which were members of genera Thraustochytrium, Aplanochytrium, Oblongichytrium, Ulkenia, Labyrinthula and undescribed novel phylotypes. Results of this study indicated unprecedented high diversity of labyrinthulomycetes as well as the presence of novel labyrinthulomycetes and thraustochytrids lineage, and also provided new information on the significant role of thraustochytrids in microbial food webs in a coastal marine ecosystem.

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