Continuous cultivation of Clostridium thermobutyricum in a rotary fermentor system

The growth behavior of Clostridium thermobutyricum JW171K and its production of butyric acid were investigated under continuous cultivation in a recently developed rotary fermenter. Using sow dilution rates (up to 40 times the shortest doubling time), the continuous culture conditions caused metabolic shifts from butyrate formation to the production of acetate, Using an 18-h volumetric retention lime, no true steady state in butyrate formation was achieved after 22 days, although the optical density was stable. Acetate and butyrate were formed in an oscillatory mode with an alternating predominance between these two products, indicating an oscillation between the less exergonic acetate-forming but higher ATP (4ATP mol(-1) glucose) forming mode, and the more exergonic butyrate and 3ATP mol(-1) glucose forming mode. During the continuous culture drastic changes in cell morphology occurred and, at the lower dilution rates, long, granulose-containing, filamentous cells with rounded protuberances and swellings were observed, A maximal butyrate concentration of 18.4 g L-1 and a productivity of about 2.4 g L-1 per h (at 25-27 mM concentration in the broth) were obtained.