Overexpression of the primary sigma factor gene sigA improved carotenoid production by Corynebacterium glutamicum: application to production of β-carotene and the non-native linear C50 carotenoid bisanhydrobacterioruberin. Corynebacterium glutamicum

Corynebacterium glutamicum shows yellow pigmentation due to biosynthesis of the C50 carotenoid decaprenoxanthin and its glycosides. This bacterium has been engineered for production of various non-native cyclic C40 and C50 carotenoids such as β-carotene, astaxanthin or sarcinaxanthin. In this study, the effect of modulating gene expression more broadly by overexpression of sigma factor genes on carotenoid production by C. glutamicum was characterized. Overexpression of the primary sigma factor gene sigA improved lycopene production by recombinant C. glutamicum up to eight fold. In C. glutamicum wild type, overexpression of sigA led to two fold increased accumulation of the native carotenoid decaprenoxanthin in the stationary growth phase. Under these conditions, genes related to thiamine synthesis and aromatic compound degradation showed increased RNA levels and addition of thiamine and the aromatic iron chelator protocatechuic acid to the culture medium enhanced carotenoid production when sigA was overexpressed. Deletion of the gene for the alternative sigma factor SigB, which is expected to replace SigA in RNA polymerase holoenzymes during transition to the stationary growth phase, also increased carotenoid production. The strategy of sigA overexpression could be successfully transferred to production of the non-native carotenoids β-carotene and bisanhydrobacterioruberin. Production of the latter is the first demonstration that C. glutamicum may accumulate a non-native linear C50 carotenoid instead of the native cyclic C50 carotenoid decaprenoxanthin. Overall design: Differential expresssion under sigA overexpression was evaluated at two different growth stages (8 hours and 24 hours after inoculation), comparing with the empty vector control.