Evaluation of Amycolatopsis mediterranei VA18 for production of rifamycin-B

Abstract

Comparative studies were performed to develop a fermentation process for the production of rifamycin-B using Amycolatopsis mediterranei VA18. Wheat bran as substrate in solid state fermentation (SSF), and peanut meal and soybean with glucose were used as substrate for submerged fermentation (SmF). Various process parameters including moisture and pH of the substrate, inoculum size, temperature and period of incubation were optimised for rifamycin-B production. For SmF, the optimal conditions were 10% (v/v) inoculum, pH 7.2, incubation temperature 30°C with a fermentation period of 6 days. When SmF was carried out in fermenter with controlled aeration (1.5 vvm) and dissolved oxygen level (80%), rifamycin production increased to about 1.5-fold greater than the flasks. SSF was, in general, superior to SmF conducted in flasks or fermenter. Optimal conditions for SSF were 7.2 substrate pH, 30% (v/v) inoculum size and incubation at 32°C for 9 days. As the content of substrate moisture increased in SSF, rifamycin production also increased and highest yields were obtained when fermentation was carried out using 90% moisture, which led practically to semi-solid-to-slurry conditions of fermentation. With 70% substrate moisture (SSF conditions), rifamycin production was about 15 g/kg which was about 31 g/kg with 80% moisture. Maximum production (rifamycin-B, 39 g/kg substrate) was obtained with 90% substrate moisture, which was almost 16-fold higher than that obtained in the fermenter (SmF). Ethyl acetate appeared as the most suitable organic solvent for the extraction of the antibiotic from the fermented material.