Methods are provided to obtain recombinant microbial cells having at least one genetic modification that increase the buoyant density of a recombinant microbial cell or the buoyant density of inclusion bodies produced within a recombinant microbial cell. Exemplified are genetic modifications that increase the buoyant density of a recombinant microbial cell expressing heterologous peptides and polypeptides. Increasing expression of the genes ysaB, glyQ, glyS or a combination thereof within the recombinant microbial cell produces cells or inclusion bodies having higher buoyant density. A similar effect was achieved by decreasing or disrupting expression of the endogenous gltA gene. Increases in buoyant density render peptide production more efficient with respect to time and costs.