The effects of agitation by a flat-bladed turbine impeller on the microbial production of xanthan gumwere studied. The results showed that the intensity of shear flow of an impeller was particularly important compared with other physical factors relevant to agitation. It was also observed in an equipment of defined shear rate that the specific production rate of xanthan gumand the specific oxygenuptake rate were influenced by the shear stress but not by the shear rate. Both of these rates increased with increasing shear stress in the range of 0-40Pa, beyond which they were constant. Increase in glucose concentration, as the driving force of glucose transfer from the mediuminto the cells, resulted in increase of the specific production rate of xanthan gum. These results suggest that the shear stress was particularly important for xanthan gumproduction and that the microbial production of xanthan gummight be limited by the mass transfer of the materials from the mediuminto the cells at low shear stress.

Fusarium equiseti M41 converts lithocholic acid to ursodeoxycholic acid. Adsorption of lithocholic acid particles to mycelia of F. equiseti M41 is essential in the conversion of lithocholic acid to ursodeoxycholic acid. Production of ursodeoxycholic acid was negligible when particles of lithocholic acid were absent. As the concentration of lithocholic acid particles increased, both the amount of mycelium-bound lithocholic acid and the production of ursodeoxycholic acid increased hyperbolically (K1/2 = 1.9 g/liter and K = 1.9 g/liter. A fluorescent lithocholic acid derivative was used to confirm that insoluble particles of litl;PcTolic