Optimization of Culture Conditionsand Analysis of Fermentation Process for Plant Vaccine-producing Bacterium, FJAT-1458

Conditions to culture FJAT-1458, a bacterium that produces plant vaccine against the tomato bacterial wilt caused by Ralstonia solanacearum, were optimized by asingle factor experiment. They were determined to be the use of an SPA medium containing peptone 5 g·L^-1, sugar 20 g·L^-1, KH₂PO₄0.5 g·L^-1, and MgSO₄0.25 g·L^-1 at 30℃ with 35 mL of broth in a 250 mL shaking flask. Subsequently, in a 50 L fermentation tank, the fermentation was carried out and the process monitored. During the fermentation, the cell count on FJAT-1458 increased initially and followed by a gradual decline with a 4-stage growth period that included the adaptive (0-6 h), logarithmic (6-36 h), stationary (36-60 h), and decline phases (after 72 h). In addition, it was observed that(a) the pathogenicity indicator, attenuation index, of FJAT-1458 ranged from 0.832 to 0.855 showing no significant difference (P>0.05) throughout the entire process; (b) the pH of the fermentation broth increased from 7.23 to 8.78; (c) morphologically, the bacteria appeared to be(1.0-1.5)μm×(0.5-0.8)μm rods with a darkening color as the process proceeded; (d) the cellular secretion from the bacteria increased with time; and, (e) some of the bacterial cells deformed and lysed near the end of fermentation.