Product formation by a nitrogen limited culture of Beneckea natriegens in a chemostat in the presence of excess glucose

Summary

Beneckea natriegens was grown in continuous culture at various growth rates under nitrogen limitation in the presence of excess unmetabolised glucose. The bacterial protein content (% dry weight) varied significantly with growth rate, but as the absolute amount of bacterial protein in the culture was independent of growth rate the latter was used in the calculation of kinetic data instead of bacterial dry weight. Under carbon-excess conditions glucose was overmetabolised to extracellular products and a maximum yield of 0.53 g product C·g⁻¹ glucose C was observed at D=0.04 h⁻¹. The yield of soluble metabolic products decreased and the yield of cells increased with increasing growth rate.

Although the rate of total product carbon production increased with growth rate, the concentration of products decreased with growth rate. Oxoglutarate and ethanol were the two major products identified and at D=0.04 h⁻¹ accounted for 53% of the product carbon. Ethanol was produced under fully aerobic conditions and its rate of production was independent of growth rate, as observed for oxoglutarate. Although the yield of products was high at low growth rate (Yp=0.53 gC·g⁻¹C at D=0.04 h⁻¹) the rate of glucose uptake expressed under these conditions was only a fraction of the maximum uptake rate capable by the organism. Surprisingly, under carbon-excess conditions the respiration rate was tightly controlled as the YO₂ of both carbon limited and excess cultures were virtually identical at all growth rates examined.