Glycogen formation in Corynebacterium glutamicum and role of ADP-glucose pyrophosphorylase

Abstract

Glycogen is generally assumed to serve as a major reserve polysaccharide in bacteria. In this work, glycogen accumulation in the amino acid producer Corynebacterium glutamicum was characterized, expression of the C. glutamicum glgC gene, encoding the key enzyme in glycogen synthesis, ADP-glucose (ADP-Glc) pyrophosphorylase, was analysed, and the relevance of this enzyme for growth, survival, amino acid production and osmoprotection was investigated. C. glutamicum cells grown in medium containing the glycolytic substrates glucose, sucrose or fructose showed rapid glycogen accumulation (up to 90 mg per g dry weight) in the early exponential growth phase and degradation of the polymer when the sugar became limiting. In contrast, no glycogen was detected in cells grown on the gluconeogenic substrates acetate or lactate. In accordance with these results, the specific activity of ADP-Glc pyrophosphorylase was 20-fold higher in glucose-grown than in acetate- or lactate-grown cells. Expression analysis suggested that this carbon-source-dependent regulation might be only partly due to transcriptional control of the glgC gene. Inactivation of the chromosomal glgC gene led to the absence of ADP-Glc pyrophosphorylase activity, to a complete loss of intracellular glycogen in all media tested and to a distinct lag phase when the cells were inoculated in minimal medium containing 750 mM sodium chloride. However, the growth of C. glutamicum, its survival in the stationary phase and its glutamate and lysine production were not affected by glgC inactivation under either condition tested. These results indicate that intracellular glycogen formation is not essential for growth and survival of and amino acid production by C. glutamicum and that ADP-Glc pyrophosphorylase activity might be advantageous for fast adaptation of C. glutamicum to hyperosmotic stress.