Biological conversion of rifamycin B by live Humicola sp. cells immobilized in a dual hollow fiber bioreactor

The biological transformation from rifamycin B to rifamycin S was carried out with the live whole cells of Humicola sp., ATCC 20620, immobilized in a dual hollow fiber bioreactor (DHFBR). Humicola sp., inoculated in the DHFBR, proliferated successfully to a high density cell mass within the space between an outer silicone tubing and three inner polypropylene hollow fiber membranes. In order to control the cell growth a nitrogen deficient medium was fed. Conversion of rifamycin B continued for more than 30 d, whereas that of immobilized rifamycin B oxidase lasted only for 3 d in comparable conditions.In the DHFBR the volumetric productivity of rifamycin S was 0.65–1.03 mmol/(dm³ · h) with 60% conversion, while that in the rotating packed disk reactor was 0.27 mmol/(dm³ · h) with 40% conversion at a residence time of 0.5–1.5 h.