Gallidermin, produced by Staphylococcus gallinarum Tü 3928, is a type-A
lantibiotic with potential for the treatment of multidrug-resistant
infections from Gram-positive pathogens such as methicillin-resistant S. aureus. In order to eliminate product inhibition as a reason for so far very modest product titers in S. gallinarum cultivations, we recently developed a novel two-stage production strategy based on the production of a non-toxic
gallidermin precursor - pregallidermin - by an engineered strain and the subsequent conversion of the precursor to
gallidermin in a separate step. This directed our efforts to the identification and alleviation of cultivation constraints for the engineered strain in fed-batch cultivations based on complex media supplemented with
carbon sources, reasoning that extending the biomass production phase would lead to an extended pregallidermin production and higher titers. Substantial accumulation of
acetate occurred in fed-batch cultivations with either
maltose or
glycerol - but not
succinate - as an additional
carbon source. Reductions in feeding rate to limit
acetate accumulation led in turn to increased product degradation. Based on these observations, we developed an optimized exponential feeding strategy that allowed the process to reach a biomass concentration of 120gL(-1) and a product concentration of 1.23gL(-1) pregallidermin, corresponding to 0.780gL(-1) mature
gallidermin, a 2.5-fold increase over previous processes.