Continuous microbiological transformation of steroids.

Continuous fermentation trials on the bioconversions of pregnadiene to pregnatriene by Septomyxa affinis and progesterone to 11alpha-hydroxyprogesterone by Rhizopus nigricans were conducted successfully in an eight-stage pilot plant reactor. The first stage was used as the mycelial growth stage while the steroid solutions were added continuously to stage 2, thus using the remaining stages as conversion vessels. Recoveries of 50 to 60% oxidized steroid (based on total steroid supplied) were obtained in both cases upon a contact time of 5 hr between mycelium and steroid. Longer contact times resulted in a gradual net loss of steroid. It was concluded that two-stage reactors (one growth stage and one conversion stage) were adequate for efficient continuous operation of such processes. The reaction volumes of both stages have to be kept in proper balance to insure optimal holdup times for both the cell growth and conversion steps.