Culture of Azetobacter vinelandii with acetate as carbon source under oxygen limitated conditions

We studied discontinuous and fed-batch cultures of Azotobacter vinelandii on acetate under oxygen limitation conditions, with the intention of using them as a Model System for the experimental study of oxygen transfer intensification methods in aerobic fermenters. Using a discontinuous culture, three series of experiments were carried out: one under the simplest conditions for the application of this system to an aerobic fermenter, with no pH control and under atmospheric nitrogen-fixing conditions; the other two series were performed with pH control and under atmospheric nitrogen-fixing conditions and with NH4Cl as the nitrogen source, respectively. We determined the overall kinetic parameters for both exponential growth and linear growth (with oxygen limitation). An increase in the stirring speed did'nt have influence on the specific growth rate but produced a higher specific oxygen and carbon source consumption rate. The nitrogen source was also seen to have an evident influence on the specific rate of consumption of the substrate, which was greater under nitrogen-fixing conditions. As regards the specific growth rate, A. vinelandii seems to prefer acetate to glucose and ammonia to atmospheric nitrogen. In a fed-batch culture, i.e. a discontinuous culture with acetate as the carbon source and using a concentrated solution of acetic acid to keep pH levels constant, two series of experiments were carried out. As the concentration of the carbon source was kept constant, we were able to analyse, independently, the damage suffered by the microorganism as it grew during variable time periods under oxygen limitation conditions. There was seen to be a diminution of mu when growth time under oxygen limitation conitions was increased.