Molasses, Glucose, Fructose, Sucrose, and Starch

Traditionally, amino acid production by C. glutamicum is based on molasses or on starch hydrolysates. These substrates have competing uses in human nutrition. Sugar beet or sugarcane molasses are used mainly in Europe, South America, and Asia [113]. Molasses contains between 40% and 47% sugar, primarily sucrose, but also glucose and fructose that are present up to 12% in raw molasses. 

The disaccharide sucrose is imported by a specific phosphotransferase system PTSjuc responsible for uptake and phosphorylation of sucrose [125], yielding sucrose-6-phosphate. Sucrose-6-phosphate hydrolase then yields glucose-6-phosphate and free fructose [107, 127]. Fructose is exported out of the C. glutamicum cell and re-imported by PTSf, with concomitant phosphorylation to fructose-l-phosphate [128]. Overexpression of the fructose bisphosphatase genefbp improved L-lysine product yields on sucrose [46]. 

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