Development of streptomyces to utilise sustainable feedstock in fermentations

Abstract

The genus Streptomyces is comprised of soil-dwelling Gram-positive Actinobacteria that are widely used for the industrial production of antibiotics. S. clavuligerus is used for the industrial production of clavulanic acid, which is a potent b-lactamase inhibitor, and is, therefore, able to restore the sensitivity of b-lactamase-producing bacteria penicillins and cephalosporins. In fermentations, the carbon sources available for utilisation by the producing organism have profoundly impact central carbon and specialised metabolic pathways. We have a long-term goal of using carbon sources from food waste to produce clavulanic acid with a view to developing more sustainable fermentations. To achieve this, the carbon utilisation profile of S. clavuligerus has to be diversified. Wildtype S. clavuligerus is a natural glucose auxotroph and has adapted to utilise glycerol most efficiently. It has been shown that the lack of glucose utilisation by S. clavuligerus is due to the insufficient expression of genes whose products are required for glucose uptake (glcP) and phosphorylation (glk). To enable glucose utilisation by S. clavuligerus strains, we have constructed strains for heterologous expression of either glcP or glk from different Streptomyces species. Further, the range of utilisable carbon sources for growth and clavulanic acid production has been investigated. Growth on solid media has revealed interplay between carbon and nitrogen metabolism, with extracellular protease production being regulated in a carbon source-dependent manner. Therefore, the role of protease secretion and its relationship with clavulanic acid production has been examined, revealing a complex role between carbon catabolite repression, protease production and clavulanic acid biosynthesis.