Secretory production of homologous and heterologous proteins by recombinant Streptomyces: What has been accomplished?

Streptomyces are gram-positive mycelial soil bacteria with a complex morphological and physiological life cycle, culminating in the formation of spores accompanied by the production of a huge variety of secondary metabolites. The free-living saprophytic Streptomyces species are well-known producers of a great variety of extracellular enzymes, including amylases, cellulases, xylanases, phosphatases, lipases, proteinases, and nucleases, as well as numerous secreted proteinaceous enzyme inhibitors. Recently, a gene that codes for a small DNA-binding protein (saf) increased the secretory production of several extracellular enzymes on expression in S lividans. The sof-overexpressing strains might be valuable host strains for the secretory production of recombinant proteins in streptomyces. Although the optimal temperature for the growth of the recombinant strain was 29 C, the optimal temperature for the secretory production of xylanase by the same strain was 34 C. The history of Streptomyces species as alternative hosts for the secretory production of homologous and heterologous proteins is rather short.