The microbial loop stresses the importance of flagellated protozoa as predators of bacteria and regenerators of nutrients, the outcome of which affects higher trophic levels. The element stoichiometry of flagellates has only been examined while feeding upon bacteria or phytoplankton. In this study, the element stoichiometry of the protozoan flagellate, Ochromonas danica, was determined while growing osmotrophically thus eliminating the potential errors due to element contributions of prey in food vacuoles.

The element and nucleic acid content of the flagellate were examined under a range of environmentally relevant temperatures and growth rates using chemostat cultures. Growth rate was the driving force of change for the element content of the flagellate, temperature and the interaction of temperature and growth rate played very small roles in variation. These results and results of previous studies of flagellates predict that flagellates may be weakly homeostatic.