PA-003:

High abundance of heterotrophic nanoflagellates in the oxic-anoxic interface of meromictic Lake Suigetsu, Japan

Vertical distributions of heterotrophic nanoflagellates (HNF) were studied in the meromictic Lake Suigetsu, Japan. HNF are generally studied as a whole, whereas the knowledge about the ecology of individual groups or species remain unknown. To study the abundance of a ubiquitous group and a facultative anaerobic species of HNF in a meromictic lake, Catalyzed Reporter Deposition-Fluorescence In Situ Hybridization (CARD-FISH) was used. CARD-FISH species-specific probe PLA1241 was constructed targeting a species (Suigetsumonas clinomigrationis) of HNF isolated from Lake Suigetsu. Group-specific probes (KIN516 and Euk516 competitor) targeting kinetoplastid flagellates were also used. Vertical sampling from 5 depths was conducted in October 2014. Abundance of total flagellates was found to be in the range of 1- 4 X 10⁴ cells ml^-1, with maximum abundance of heterotrophs in the oxic-anoxic interface layer. The abundance of kinetoplastids were relatively high in the oxic surface waters but were found to be less abundant in the anoxic waters. However, highest abundance (1.2 X 10³ cells ml^-1) of kinetoplastids were recorded from the interface. The abundance of S. clinomigrationis was also found to be the highest (7.8 X 10² cells ml^-1) in the interface, whereas low abundance was detected from the surface waters. Their abundance in the anoxic water was slightly higher due to their facultative lifestyle. The highest abundance of kinetoplastids, S. clinomigrationis or total HNF were recorded from the interface waters that allow the growth of various HNF species living in freshwater and marine and also aerobic and anaerobic environments.

keywords:Heterotrophic nanoflagellates,CARD-FISH,Suigetsumonas clinomigrationis,Kinetoplastid flagellates,Lake Suigetsu