The production of rifamycin B was c

The production of rifamycin B was carried out in a 6.6 litre
laboratory glass fermentor (Bioflo 3000 Benchtop fermentor, New
Brunswick Scientific Co., NJ, USA). The inoculum in a
concentration of 5% was added to 2.5 litres of F2m1 medium,
unless otherwise indicated. Agitation was carried out using 2 six
blade Rushton impeller separated by 9.5 cm with the lower impeller
2.5 cm above the agitator tip. Aeration using a multiorifice ring
sparger was controlled by a pressure regulator and monitored by a
flowmeter. The percent dissolved oxygen (DO) was monitored
and/or controlled through the fermentor’s control unit using
polarographic DO probe. DO control was achieved by cascading
the airflow and the agitation speed simultaneously. The pH was
monitored by a pH electrode; calcium carbonate was omitted from
the medium when the pH was automatically controlled by the
fermentor’s control unit, which applied 1N HCl, and 1N NaOH
actuated by peristaltic pumps. The temperature was adjusted at
28°C, the agitation rate at 500 rpm and the aeration rate at 1 vvm,
unless otherwise indicated. Foam was suppressed by sterile
sunflower oil using a foam controller pump and a foam probe.
Samples were taken every 24 h and rifamycin B concentration,
remaining glucose or reducing sugars concentrations, dry cell
weight and, where indicated, viscosity of the broth mixture was
determined. For fed-batch experiments, aliquots of 150 ml of
glucose, 150 ml of glucose syrup, 150 ml of soytone, 25 ml of yeast
extract were taken from sterile stock solutions containing suitable
concentrations, and added to the fermentation culture at the
indicated times to give the required final concentrations