Hydrocarbon degradation by Acinetobacter calcoaceticus RAG-1 using the self-cycling fermentation technique

The use of self-cycling fermentations (SCFs) as a method for dealing with insoluble carbon substrates was examined. The emulsan-producing Acinetobacter calcoaceticus RAG-1 was used as the test organism. Limiting concentrations of hexadecane, 1-hexadecene, or 1-chlorohexadecane were used as the carbon substrate. The parameters monitored were residual hydrocarbon concentration, cycle time (doubling time), biomass concentration and emulsan concentration. Cycle-to-cycle variations of the measured parameters were found to be samll. In all cases, no residual hydrocarbon was detected. The minimum dissolved oxygen concentration was found to correspond with the complete dissappearance of the carbon source. A correlation between minimum dissolved exygen concentration, biomass concentration, and emulsan concentration was noted, thus making it easy to determine when steady-state conditions had been reached with respect to biomass and emulsan concentrations. The specific emulsan and biomass yields were found to increase during early stages of the fermentation, attaining their respective maxima at steady-state. Foaming problems often associated with the complete utilization of the insoluble substrate were eliminated using SCF technology, because harvesting occurs immediately following carbon depletion. From the results, SCFs provide a convenient method by which to produce and harvest emulsan.