Semisolid state fermentation: effects of beet sugar root : peptone ratio on erythromycin production by Saccharopolyspora erythraea NCIMB 12462

Background and objectives Erythromycin, a prominent member of the macrolide antibiotics, is commercially produced by submerged fermentation. However, this process requires high energy expenditures. The objective of the present work was to improve and optimize the cultural conditions of Saccharopolyspora erythraea NCIMB 12462 grown under semisolid state fermentation, with less energy requirements, less waste water generation, and easier product recovery, for the production of erythromycin using beet sugar root (BSR) and peptone. Materials and methods Chemical analysis of BSR was carried out according to the guidelines of AOAC and using high-performance liquid chromatographic. The concentration of erythromycin was measured using the agar diffusion bioassay method. Evaluation of different nitrogen sources for erythromycin production was carried out and the effect of different BSR : peptone ratio on erythromycin production was determined. The impact of initial moisture content (75-88%), size of inoculum, sodium chloride and calcium carbonate concentrations, and incubation period (1-12 days) on erythromycin production using solid state fermentation by S. erythraea NCIMB 12462 was evaluated. Results and discussion Optimization of environmental and culture parameters, concentration of nitrogen sources (ammonium sulfate, yeast extract, and peptone), BSR/peptone ratio, inoculum size, moisture content, and incubation time exhibited a significant increase in erythromycin production compared with the production before optimization. The concentration of erythromycin in optimized medium was 735.65 ± 8.58 μg/g dry BSR (1.36 times more than that of the control medium). The optimal conditions for erythromycin production using solid state fermentation for BSR were a initial moisture level of 77.78%, inoculum size of 2 × 10 6 -2 × 10 7 spores/10 g dry BSR, incubation period of 10 days, and peptone at a concentration of 0.8 g/100 g BSR.