Effects of temperature on cell growth and xanthan production in batch cultures of Xanthomonas campestris

Batch xanthan fermentations by Xanthomonas campestris NRRL B‐1459 at various temperatures ranging between 22°C and 35°C were studied. At 24°C or lower, xanthan formation lagged significantly behind cell growth, resembling typical secondary metabolism. However, at 27°C and higher, xanthan biosynthesis followed cell growth from the beginning of the exponential phase and continued into the stationary phase. Cell growth at 35°C was very slow; the specific growth rate was near zero. The specific growth rate had a maximum value of 0.26 h −1 at temperatures between 27°C and 31°C. Cell yield decreased from 0.53 g/g glucose at 22°C to 0.28 g/g glucose at 33°C, whereas xanthan yield increased from 54% at 22°C to 90% at 33°C. The specific xanthan formation rate also increased with increasing temperature. The pyruvate content of xanthan produced at various temperatures ranged between 1.9% and 4.5%, with the maximum occurring between 27°C and 30°C. These results suggest that the optimal temperatures for cell growth are between 24°C and 27°C, whereas those for xanthan formation are between 30°C and 33°C. For single‐stage batch fermentation, the optimal temperature for xanthan fermentation is thus dependent on the design criteria (i. e., fermentation rate, xanthan yield, and gum qualities). However, a two‐stage fermentation process with temperature shift‐up from 27°C to 32°C is suggested to optimize both cell growth and xanthan formation, respectively, at each stage, and thus to improve overall xanthan fermentation.