Morphological, phylogenetic and biogeographic characterizations of three heterotrophic nanoflagellates isolated from coastal areas of Korea

ABSTRACT

Heterotrophic nanoflagellates (HNFs, 2–20 μm in size) are important bacterivores in aquatic environments. We isolated and distinguished three HNF strains from Korean coastal samples: Ancyromonas kenti strain KM086, Cafeteria mylnikovii strain JS001 and Multimonas media strain JS004. Their 18S rDNA sequences aligned with previously known counterparts. Under light microscopy, all strains match their previous respective species descriptions. However, under scanning electron microscopy, strain JS004 shows some features at odds with prior observations of M. media, including different putative extrusomes, an ‘unfrilled’ skirt margin, and a putative ‘tusk’. We also used the V4 region of 18S rDNA to study species distribution globally using Malaspina-2010 data from 122 surface stations and 13 various depth stations. Intriguingly, we found that A. kenti was most abundant in low-oxygen conditions of the bathypelagic zones (1000–4000 m deep) in the Pacific Ocean, suggesting a specialization for thriving in low-oxygen habitats. In contrast, we only found M. media represented at one surface site, and C. mylnikovii was not found at all. Thus, A. kenti may be one of the most important feeders on bacteria in the bathypelagic zones with low-oxygen concentrations, while the other two isolates appear to be rare species in marine systems.

KEYWORDS:

• Classification
• heterotrophic nanoflagellates
• morphology
• phylogenetic tree
• global distribution pattern

Acknowledgements

We thank Won Je Lee for assistance with sampling.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Institute of Biological Resources (NIBR) under grant (NIBR202333201), funded by the Ministry of Environment (MOE) of the Republic of Korea; Korea Institute of Marine Science and Technology (KIMST) under grant (RS-2023-00256330), funded by the Ministry of Oceans and Fisheries (MOF); and the National Research Foundation of Korea (NRF) grant to JSP funded by the Korean government (NRF-2022R1I1A2064117).