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

Abstract

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 dilution rate, probably due to an overcapacity of the micro-organism to oxidise methanol. Using a modified Monod equation, the growth parameters were calculated as follows: μ max=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, formaldehyde dehydrogenase and formate dehydrogenase increased in the cell free 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 formate dehydrogenase was greater than that of formaldehyde dehydrogenase, probably 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 dehydrogenase are less affected by the shift of the dilution rate, whereas the rate of the specific synthesis for formaldehyde dehydrogenase is strongly dependent on the dilution rate. The maximum productivity of the enzymes was predicted 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 formate dehydrogenase, respectively.