Factors effecting the biomass enhancement of Propionibacterium sp.

Propionibacterium technicum is the aerotolerant anaerobic bacteria which can produce vitamin B12, propionic and acetic acids. The study of factors affecting the growth conditions of the bacteria in stationary flask is carried out by modification of the complete medium's formula recipe. The modified recipe, so-called "Optimized medium" is composed of (percent): 1.5 glucose, 2.0 yeast extract, 0.16 NaH2PO4, 0.16 K3PO4 and 0.04 MgCl2.6H2O at pH 7.0 using 6 percent of the inoculated culture (A660=3.0) after 24 hours culture at 32 deg C. In the Optimized medium, the bacteria grow 12 percent better than in Complete medium with the cell dry weight contents up to 4.88 g/l within 96 hours incubation time. When the bacterial culture was grown in 5-L batch fermentor with glucose concentration at 1.9 percent and at 400 rpm agitation speed, the cell yield was up to 8.72 g/l within 26.5 hours. In the fermentation system with aeration started after 24 hours incubation time, the culture reached the maximum cell growth at 27 hours with the yield of 9.03 g/l dry weight whereas propionic acid was reduced 34.2 percent. Fed-batch cultivation was also performed. In the exponential fed-batch with starting glucose concentration at 1.9 percent, it was found that the bacterial culture could not use up the added glucose with the yield was 7.06 g/l within 33 hours incubation time. With starting glucose concentration of 0.5 percent of 3-L culture, optimized medium which glucose content of 4.0 percent was added to the culture 2-3 times until the total volume reached 5 L. The yield was obtained at slightly lower to that of the batch fermentation, so were the secreted propionic and acetic acids. The intermittent fed-batch culture showed the feeding time is essential for the cell growth of this bacterium, so 50.0 percent glucose solution was added after the starting glucose content of 1.9 percent had been decreased by half. The final yield of harvested cells within 58 hours incubation time was 30.40 g/l, 4.27 times more than that obtained from the batch fermentation. In addition, the viability of the preserved cells under deep freezing and lyophilization techniques was studied. It revealed that the survival rate of both methods after 15 months were similar at 26.67 and 18.33 percent, respectively.