Abstract
Streptomyces coelicolor is the best characterised streptomycete and serves as the genus model organism for biochemical, genetic and physiological studies. S. coelicolor M510 plJ8714, a strain that expresses actinorhodin (ACT) constitutively was examined. A series of chemostat cultures, operating over a range of growth rates, was subjected to metabolic flux analysis using the metabolite balancing technique. Using stepwise iterative correlation of the ACT production rate with the fluxes of every reaction in the network, the strongly correlating (positive and negative) reactions that could be used for a metabolic engineering approach to enhance antibiotic productivity were identified. The reaction showing the strongest correlation with ACT biosynthesis, across all the dilution rates, was glutamate-5-phosphate biosynthesis (r=0.97). This reaction diverts carbon flux away from oxaloacetate resulting in higher flux to acetyl CoA, the ACT precursor. Similarly, lysine biosynthesis also correlated strongly with ACT (r=0.95). It also diverts oxaloacetate from its acetyl CoA draining reaction. When negatively correlating reactions were examined, those of TCA cycle correlated strongly, especially citrate biosynthesis (r=0.95). This is obvious as citrate competes directly with ACT for acetyl CoA. This analysis suggested that feeding glutamate, citrate, and lysine should enhance antibiotic production. Results from feed experiments were consistent with the findings. ACT production was improved by 56%, 44%, and 13% in glutamate, citrate, and lysine fed cultures respectively. This also coincided with results from elementary modes analysis, which found that citrate and glutamate can also be used as carbon sources for ACT production. Two reactions with low/medium correlation coefficients were also tested, leucine biosynthesis (r=0.90) and glutamine biosynthesis (r=0.89). According to correlation analysis, feeding leucine should decrease ACT production whilst feeding glutamine should increase, but the effect of both should be insignificant. The results showed that ACT production was decreased by 20% in leucine feed and no effect on ACT production was seen in glutamine feed. The results from this study suggest the usefulness of metabolic flux analysis in helping design process to improve antibiotic in the organism.