A simulation model for the effect of predation on bacteria in continuous culture.

A simulation model was developed for the carbon (C), nitrogen (N), and phosphorus (P) content of bacteria and their medium in a chemostat. Cell components distinguished included the structural component, synthetic machinery, building blocks and intermediates, C reserves, ammonium (NH4), orthophosphate (PO4), and polyphosphate. Growth, incorporation of substrates, and production of waste products were related to physiological status, as indicated by the amounts of various cell components. The model was fitted to data from chemostats on the chemical composition of bacteria growing in C-, N-, and P-limiting media and was used to explore the consequences of predation on bacterial populations. In C-limiting media predation (without the return of nutrients to the medium by the predator) increased NH4 uptake in spite of a decrease in bacterial biomass. In N-limiting media predation decreased both biomass and the rate of N uptake. These results were accounted for by the effect of growth rate on bacterial N demand. In C-limiting media the return of NH4 and PO4 by the predator did not change the effect of predation on bacteria. But in N-limiting media the return of nutrients decreased the effect of predation on biomass, and stimulated respiration and NH4 uptake by the bacteria. The effect of growth rate on the chemical composition of bacteria was proposed as a possible explanation of the stimulatory effect of predators on bacteria.