Mutational Selection and Characterization of a Lysine-Producing Strain of Corynebacteriumglutamicum

Bacterial strains of Corynebacterium glutamicum isolated from various natural environments were initially selected for their capacity to accumulate glutamic acid and then subjected to EMS chemical mutagenesis. Strains were then selected for amino acid auxotrophies and their capacities to produce other amino acids (notably lysine) were examined. A strain initially isolated from bird droppings and having a double auxotrophy for threonine and methionine was thus selected and retained for characterization as to its capacity to produce significant amounts of lysine. This strain grew at rates approximately half that of the parent strain but accumulated lysine as a primary metabolite throughout growth. Final concentrations of approximately 50 g/L lysine could be produced on glucose medium and this fermentation limit was shown to be directly related to the end concentration of lysine. Glucose was shown to be the best carbon source though sucrose showed similar capacity albeit with slightly diminished rates of sugar consumption and lysine accumulation. Acetate gave only relatively poor fermentation performance. Bearing in mind that only a single generation of mutational selection was necessary to attain this performance, the strain shows interesting potential for further development.