Comparison Of The Ingestion And Digestion Rates Of Ochromonas danica Grazing On Pseudomonas fluorescens Of Varying Food Quality

Abstract

Flagellate prey selection appears to depend on morphological characteristics of prey such as cell size and motility, as well as on physiochemical characteristics such as digestibility and cell surface characteristics. Pseudomonas fluorescens was grown in chemostats at four dilution rates (0.03, 0.06, 0.10, 0.13 h-1) and three temperatures (14, 20, 28°C) to produce cells of varying morphological characteristics (cell size) and physiochemical characteristics or food quality (as determined by the C:N:P ratio). Heat-killed bacteria of a given food quality were prepared and used to grow the flagellate Ochromonas danica. Ingestion and digestion rates were determined using fluorescently labeled bacteria of the same food quality as the bacteria supporting growth. Ingestion rates were affected by both food quality and cell size. Cells of high food quality (low carbon:element ratio) were ingested at higher rates than cells of low food quality. Multiple regression analysis indicated that cell size also influenced ingestion rate but to a much lesser extent than did food quality. Digestion rates were not correlated with either food quality or cell size. Results suggest that flagellates my use chemosensory cues to preferentially select food items.