Carbon, nitrogen, and phosphorus budgets for the mixotrophic phytoflagellate Poterioochromonas malhamensis (Chrysophyceae) during bacterial ingestion

Growth, grazing, C and nutrient in corporation by the mixotrophic phytoflagellate Poterioochromonas malhamensis were examined under various nutrient and light regimes in the presence of heat‐killed bacteria. Poterioochromonas malhamensis readily ingested bacteria in all culture treatments containing heat‐killed bacteria, and growth rates of the protist were much greater for heterotrophic (bacterivorous) growth than for phototrophic growth. C incorporation efficiencies by the phytoflagellate were virtually identical to P incorporation efficiencies during heterotrophic growth, but N incorporation efficiencies were somewhat lower in nearly all of the treatments. Algal growth in cultures with heat‐killed bacteria was similar in continuous darkness and in continuous light. Bacterial organic C was the primary source of protist cellular C for P. malhamensis during heterotrophic growth. Based on our observations, we conclude that P. malhamensis is primarily heterotrophic and phagotrophic and that it is highly competent in this mode of nutrition.