Role of KLa on growth and enzyme production by Acetobacter tropicalis The volumetric oxygen transfer coefficient (KLa) is one of the most important scale up factors in fermentations. KLa value affected the growth rate and enzyme activity in A. tropicalis for the production of dextransucrase. In the present study, the growth of A. tropicalis increased with increase in KLa from 0.11 to 0.28 min-1 and thereafter decreased suddenly with further increase in KLa (Figure 4). Maximum biomass (1.41 mg/ml) was obtained at 0.28 min-1 KLa. Similar pattern was observed in case of dextransurase production by A. tropicalis. Initially enzyme activity increased with increase in KLa upto a limit and
then decreased (Figure 4). Maximum dextransucrase activity (15.77 U/ml) was obtained at 0.28 min-1 KLa. This exactly coincides with the profile obtained for the growth of A.tropicalis. So, it could be concluded from the above data that higher oxygen transfer rate adversely affect the growth of A. tropicalis which in turn result in less dextransucrase production. Maximum production of proteases (15.28 UP/ml) by Staphylococcus aureus mutant RC128 was obtained when the bioreactor was operated at 300 rpm and at 2 vvm with a volumetric oxygen transfer coefficient (KLa) of 175.75 h-1 (37) In case of glucose oxidase production by recombinant Saccharomyces cerevisiae, Kapat et al. [38] concluded that KLa alone does not facilitate the specifc production of enzyme. It is the appropriate combination of impeller speed and aeration rate which is more important. Thus, the optimal DO concentration should be considered as a scale up parameter for production process instead of KLa. The major findings of the dextransucrae production by A. tropicalis in a laboratory fermenter have been summarized in Table 1.