Growth of Candida boidinii in a methanol-limited continuous culture and the formation of methanol-degrading enzymes

The growth of Candida boidinii was studied in a methanol-limited continuous culture showing a linear decrease of dry cell yield with increase of the d ilution rate, probably due to an overcapacity of the micro-organism to oxid ise methanol. Using a modified Monod equation, the growth parameters were c alculated as follows: mu = 0.152 h(-1), Y-max = 0.36 g g(-1), K-s = 1.318 g l(-1) and m(s) = 0.028 g g(-1) h(-1). The activity of methanol oxidase, fo rmaldehyde dehydrogenase and formate dehydrogenase increased in the cell fr ee extract with the decrease of the dilution rate from 0.144 to 0.019 h(-1) . Moreover, the increase of specific activity of methanol oxidase and forma te dehydrogenase was greater than that of formaldehyde dehydrogenase, proba bly due to the different affinity of the enzymes for their substrate. These results are important for the regulation of the rate of enzyme synthesis: the rates of specific synthesis for methanol oxidase and formate dehydrogen ase are less affected by the shift of the dilution rate, whereas the rate o f the specific synthesis for formaldehyde dehydrogenase is strongly depende nt on the dilution rate. The maximum productivity of the enzymes was predic ted to be 8.74, 92.2 and 15.14 U l(-1) h(-1) at dilution rates of 0.114, 0. 111 and 0.105 h(-1) for methanol oxidase, formaldehyde dehydrogenase and fo rmate dehydrogenase, respectively. (C) 1999 Elsevier Science B.V. All right s reserved.