Modelling of hexadecane degradation in continuous-flow cultures

Microorganisms of Wadden Sea sediments are able to degrade hydrocarbons in suspensions. (Berthe-Corti, L., Bruns, A., Hulsch, R., 1997. J. Microb. Methods 29, 129-137) have observed in continuous culture experiments that the growth rate of microorganisms increases roughly proportional to the dilution rate. The growth rate is nearly independent of the oxygen saturation down to about 0.5%. Even at very low oxygen supply, corresponding to an oxygen saturation far below 0.1%, growth takes place at a reduced rate. In this paper, a model is presented which can reproduce the results of these experiments. The model treats the following processes, selection of the active fraction of microorganisms growing on hexadecane, uptake of hexadecane and transformation into palmitate as a first metabolic step, synthesis of biomass, respiration and exudation. The processes are regulated by the substrate concentration, the internal palmitate quota, the exudates' concentration and an inhibiting factor. For the experiments under very low oxygen conditions, the observed growth with reduced O(2)-consumption and CO(2)-production is modelled by assuming an anoxic metabolic pathway.