Immobilized-Cell Fermentation and Bioreactor Optimization for Bioactive Metabolite Production by Streptomyces rimosus Y8
Abstract
Background: Efficient fermentation systems are important for translating microbial secondary-metabolite production from laboratory screening to reproducible bioprocesses. Objective: To evaluate calcium-alginate immobilization, repeated-batch fermentation and bioreactor configurations for production of bioactive metabolites by the highly active Streptomyces rimosus Y8 isolate. Methods: S. rimosus Y8, selected from an environmental screening program in Durg District, was cultured under optimized production conditions. Cells were immobilized in calcium alginate, and the effects of alginate concentration, inoculum amount and curing time were assessed. Optimized immobilized cells were used in repeated-batch fermentation. Antibiotic production was also compared among shake flasks, stirred and other bioreactor configurations, including an advanced fermenter at different aeration rates. Active crude metabolite was extracted and purified by silica-gel chromatography and C18 HPLC, followed by TLC and spectroscopic characterization. Results: Under optimized culture conditions, Y8 produced 0.712 g/L total active crude. Calcium-alginate immobilization produced 48.23 mg/L after 144 h using 2% alginate, a 4.501 mg inoculum and 1 h curing at 28 °C. In repeated-batch fermentation, the third cycle reached 51.63 mg/L. The advanced fermenter gave the highest reported antibiotic output among the tested systems at 1 vvm aeration. The purified Y8 product gave 99.39% reported recovery/purity by the HPLC workflow, with a retention time of 4.7 min on a C18 column using water:acetonitrile (80:20) at 254 nm. TLC showed a single spot with Rf 0.27. ESIMS showed an M+H peak at 461, corresponding to a reported molecular mass of 460 and described in the source as consistent with oxytetracycline. Conclusion: Calcium-alginate immobilization and controlled bioreactor aeration enhanced the process-development potential of S. rimosus Y8. Repeated-batch operation maintained metabolite production across cycles. Further independent validation with full massspectrometric and NMR structure elucidation, process mass balance and statistically replicated scale-up experiments is needed.