Engineering Escherichia coli to metabolize sorbitol as the sole carbon source for synthesis of recombinant L-Asparaginase-II.

Sorbitol, known as D-Glucitol, is a hexose sugar alcohol that occurs naturally in various fruits, including berries, cherries, plums, pears, and apples. It is noteworthy that sorbitol can be metabolized by microbes, plants, and humans through distinct pathways. Nevertheless, in bacteria like Escherichia coli (E. coli), sorbitol is not the primary carbon source and its utilization is generally suppressed due to carbon catabolite repression. In this context, Escherichia coli has been engineered to enable the use of sorbitol as the sole carbon source for producing recombinant proteins. This modification involves a two-plasmid system where the sorbitol-6-phosphate dehydrogenase (srlD) gene is upregulated under an araBAD promoter, while the recombinant protein is expressed from a second plasmid under the tac promoter. The overexpression of srlD in the engineered E. coli strain enhances the utilization of sorbitol as the sole carbon source. When cultured in a medium supplemented solely with sorbitol, the engineered E. coli strain exhibits a 3.6 times higher specific growth rate and yields substantially higher concentration of recombinant protein compared to the wild-type strain. Additionally, the engineered strain demonstrates a higher Y_P/X ratio than the wild-type strain.