Utilization of Dissolved Organic Carbon by Heterotrophic Bacteria and Protozoa

摘要

The research has investigated in batch and continuous culture laboratory microcosms the relationships between level and turnover rate of dissolved organic carbon substrates and the interactions among microbial populations at three trophic levels in a heterotrophic predator-prey system. Four trophic levels were measured: organic carbon substrates, the bacterium Enterobacter aerogenes (ATCC 13048), grazing ciliate Paramecium primaurelia (stock 540), and predatory ciliate Didinium nastum (ATTCC 303399). A mathematical model based on Monod kinetics was developed for this system. This research indicated that the level and turnover rate of dissolved organic carbon could profoundly affect coexistence and stability of a heterotrophic system. At high nutrient levels interference among predators permit a few prey to survive until prey became abundant and a series of oscillations resulted. When nutrient levels were reduced predators no longer interfered with each other, prey were eliminated, and only bacteria remained. The mathematical model gave a reasonable qualitative description of the observed data from continuous cultures. Actual continuous culture systems were less oscillatory than predicted by the model. No batch and continuous culture studies have previously been reported with as many trophic levels as in this research.