Feeding by heterotrophic flagellates on marine archaea

Moo Joon Lee^a, Yeong Du Yoo^b

Department of Marine Biotechnology, Anyang University, Incheon, 23038, Republic of Korea.

Archaea live in diverse habitats including extreme environments. Although they are sometimes the dominant heterotrophic organisms in microbial communities, relatively little is known about their ecological roles in microbial food webs. To explore predator–prey relationships between archaea and heterotrophic protists, we determined feeding occurrence by the heterotrophic nanoflagellates Bodo sp., Goniomonas sp., and Pedospumella sp. the common heterotrophic dinoflagellates Cryptoperidiniopsis brodyi, Gyrodinium dominans, Oblea rotunda, Oxyrrhis marina, and Polykrikos kofoidii on ammonia-oxidizing archaea (AOA) by examining the food vacuoles of these heterotrophic flagellates under an epifluorescence microscope using fluorescently labeled AOA. In addition, we measured the ingestion rates of Goniomonas sp., C. brodyi, G.dominans, and O. marina on AOA as a function of prey concentration. Cells of Bodo sp., Goniomonas sp., Pedospumella sp., C. brodyi, G.dominans, and O. marina were able to feed on AOA, whereas O. rotunda and P. kofoidii were not. With increasing initial prey concentration up to 1.7 × 106 – 9.3 × 106 cells mL−1, the ingestion rates of Goniomonas sp., C. brodyi, G.dominans, and O. marina on AOA increased rapidly but increased slowly or became saturated at higher concentrations. Although the maximum ingestion rates of the smaller flagellate Goniomonas sp. (23.1 cells predator −1 h−1) on AOA was much lower than that of the larger flagellate O. marina (296.4 cells predator −1 h−1), AOA supported the positive growth of only Goniomonas sp. The results of the present study suggest that these small heterotrophic flagellates could be effective heterotrophic protist grazers of AOA in marine ecosystems.