Growth of Bacteroidaceae in stirred fermentors.

The conditions for increasing bacterial yields in cultures of Bacteroidaceae by the use of stirred fermentors and pH control were investigated by means of three representative species: Sphaerophorus necrophorus, Bacteroides fragilis, and B. melaninogenicus. A medium containing tryptone, yeast extract, and glucose or sucrose was used. Horse serum had to be added to obtain substantial growth of B. melaninogenicus. The optimal pH for growth rate and yield was 7.0 to 7.2. Lysis of the bacteria occurred when the glucose (or sucrose) was exhausted. The rate of lysis was very high in cultures of S. necrophorus, less so in B. fragilis and B. melaninogenicus. Pleomorphism, manifested as large sperical forms of the bacteria, was observed in the late logarithmic phase of S. necrophorus. Great differences in the length of the lag phase and of the mean generation time were found among the three bacterial species. The yield in static cultures of the three species without pH control was approximately 0.4 g of dry cells per liter, but was increased, in stirred fermentors with pH control, to 3.5 g (S. necrophorus), 2.7 g (B. fragilis), and 4.3 g (B. melaninogenicus) per liter. With an inoculum density of 5 to 10 mg (dry weight) per liter, these yields were obtained in approximately 10 (S. necrophorus), 25 (B. fragilis), and 35 hr (B. melaninogenicus), respectively.