Verbesserung der Y‐Werte bei Wachstum von Hansenula polymorpha auf Methanol durch simultane Verwertung von Glucose

Abstract

The simultaneous utilization of methanol and glucose by Hansenula polymorpha MH20 was investigated in chemostat (C-limited) cultivation. The mixed-substrate utilization results in biomass yields which are greater up to 20 to 25% as expected assuming an additive growth on both substrates. This is referred to as an auxiliary-substrate effect. Additionally, methanol can be utilized a t higher growth rates in the presence of glucose compared to those obtained on this substrate alone. The extend of the auxiliary-substrate effect and the optimum ratio of substrates to reach this effect depend on dilution rate. The greatest stimulation in yield is obtained a t D -0.1 h-1, after raising the dilution rate this effect diminishes. At a rate of 0.1 h-1 the optimum mixed-substrate ratio of methanol: glucose is 7 : 1 (g). By increasing thegrowth rate the ratio changes toward glucose and reached a value of 1 : 1 (g) a t D = 0.3 h-' . This change in the optimum ratio correlates with diminution in yield coefficient of methanolp accomanying an increase in growth rate > 0.15 h-l. Energy balances of the utilization of the single substrates are used for interpretation of these results. From this it is evident that methanol does not play the role of an energyrich substrate in the metabolism of yeast.

The growth rate-limiting reaction in methanol-assimilating yeasts

“…Since methanol-grown cells are fairly sensitive to formate this idea is difficult to verify experimentally. Therefore, a methanol/ glucose mixture was used that is known to support a higher growth rate than that obtained with methanol as the sole source of carbon and energy [9,10]. Depending on the mixing ratio, methanol is assimilated simultaneously with glucose up to a D of around 0.3 h -t [11].…”

Simultaneous utilization of heterotrophic substrates by Hansenula polymorpha MH30 results in enhanced growth rates

“…Increased growth rates have already been reported for methylotrophic yeasts growing on mixtures of me-Offprint requests to: w. Babel thanol plus sorbitol Sahm 1980, 1981) and of methanol plus glucose (Egli et al 1982;Mueller et al 1983), but up to now no wholly satisfactory explanation for this has been given. However, during the simultaneous assimilation o f two heterotrophic substrates for the synthesis of a biomass unit, less of each substrate is necessary than for growth on the single substrate.…”