Sigma Factors as Potential Targets to Enhance Recombinant Protein Expression

The transcriptional factors control the expression of many genes and represent an important layer of complexity in cell factories. However, the effect of individual sigma factor deletions from a biomanufacturing perspective has not been addressed. In this contribution, growth, green fluorescence protein (GFP) expression, and oxygen consumption of Escherichia coli BW25113 strains with individual inactivation of each sigma factor were characterized under various conditions. Specific growth rate, specific GFP fluorescence, and fluorescence emission rates were compared in a mineral media and in lysogeny broth at two temperatures. rpoD has been reported to be lethal for E. coli; however, the evaluated rpoD mutant did not exhibit major growth defects in the mineral medium. This is attributed to the presence of a second copy of rpoD in this strain. GFP was expressed at three different induction levels in a mineral and LB media. The fliA mutant was the best producer in the mineral medium, whereas the rpoD mutant overperformed the other strains in LB medium. This suggests that a lower rpoD gene dosage is positive for the performance of the cell factory in a complex medium. In cultures at 20°C, the rpoS mutant exhibited the greatest recombinant expression. To our knowledge, this is the first systematic study evaluating the potential of sigma factor deletion for improving recombinant protein production.