hide
Free keywords:
bacterial ingestion; carbon metabolism; chlorophyll; chlysophyte; functional response; mixotrophic flagellate; numerical response; nutrient release; nutrient uptake; Ochromonas; phagotrophic nutrition; phototrophic nutrition
Abstract:
In laboratory experiments, I studied the influences of bacterial density and light on the ingestion and growth rates, pigment contents, and the carbon and phosphorus turnover rates of the mixotrophic flagellate Ochromonas sp. The investigated strain is a bacterivorous flagellate that can enhance its photosynthetic apparatus and grow phototrophically when bacterial densities are low. This was also evident from significantly higher chlorophyll a contents during active photosynthetic growth phases. Moderate phototrophic growth should be possible even if bacteria were absent. Bacterial ingestion rates increased hyperbolically with bacterial density, and there was no difference between light- and dark-adapted cells. Ochromonas released soluble reactive phosphorus (SRP) when growth was predominantly phagotrophic, but it took up SRP when growth was phototrophic. The mixotrophic strategy in Ochromonas appears to be bound up with costs and trade-offs: Ochromonas needs high bacterial densities to reach maximum growth rates, its basic metabolic costs are higher than for obligately phagotrophic flagellates, and its phototrophic growth rates are lower than for obligately phototrophic phytoplankton of comparable size
