Relationship between Phototrophy and Phagotrophy in the Mixotrophic Chrysophyte Poterioochromonas malhamensis

• Published in: Microbial ecology 1990-01, Vol.19 (1), p.97-109
• Main Authors: Sanders, Robert W., Porter, Karen G., Caron, David A.
• Format: Article
• Language: English
• Subjects: Algae; Animal, plant and microbial ecology; Bacteria; Biological and medical sciences; Chlorophylls; Chrysophyta; Freshwater; Fundamental and applied biological sciences. Psychology; Global carbon budget; Ingestion; Luminous intensity; Microbial ecology; Nutrition; Organic foods; Photosynthesis; Plant cells; Poterioochromonas malhamensis; Various environments (extraatmospheric space, air, water)
• ISSN: 0095-3628; 1432-184X
• DOI: 10.1007/BF02015056

The time scales involved in the transition between phototrophic and phagotrophic modes of nutrition were examined in the mixotrophic chrysophyte Poterioochromonas malhamensis. Phagotrophy began almost immediately when bacteria were added to phototrophically growing cultures of the alga, and chlorophyll a concentration per cell in these cultures decreased over a 24-hour period. Chlorophyll concentrations per cell began to increase when bacteria were grazed to a density of approximately$10^{6}\ {\rm ml}^{-1}$, but after more than 24 hours they had not returned to the higher chlorophyll concentrations observed in the phototrophically grown cultures. Bacterivory was the dominant mode of nutrition in all cultures containing heat-killed bacteria. Photosynthesis did not contribute more than ≈ 7% of the total carbon budget of the alga when in the presence of abundant heat-killed bacteria. Bacterial density was the primary factor influencing the ability of P. malhamensis to feed phagotrophically, while light intensity, pH, and the presence of dissolved organic matter had no effect on phagotrophy. We conclude that P. malhamensis is capable of phagotrophy at all times. In contrast, phototrophy is inducible in the light during starvation and is a long-term survival strategy for this mixotrophic alga (i.e., it operates on time scales greater than a diel cycle).