High cell density cultivation of Dgor/DtrxB E. coli in a chemically defined minimal medium with an enhanced iron concentration

In Escherichia coli, the production of active disulfide bonds is achieved by expression into the oxidizing periplasm, by refolding from inclusion bodies, by co-expression of a sulfhydryl oxidase and a disulfide bond isomerase, or by expression into a genetically engineered oxidizing cytoplasm. Thus, engineered strains with oxidizing cytoplasm were grown in complex media. For a large scale production and subsequently industrial relevance, growth in a highly reproducible chemically defined medium is essential. In this study, we show the enhanced need for iron for E. coli strains deficient in glutathione reductase (gor) and thioredoxin reductase (trxB). Fe(III)-citrate concentrations of 0.49 g L-1 allow the growth of E. coli Rosetta-gamiTM B(DE3)pLysS to cell densities > 65 gX L-1 in a glucose limited fed-batch. Our results show for the first time, that an E. coli strain with an oxidizing cytoplasm is able to grow to high cell densities in a chemically defined medium.