Use of formate gradients for improving biomass yield of Pichia pinus growing continuously on methanol

Abstract

Investigations were made into the improvement of growth yield (Y) of Pichia pinus MH 4 growing continuously on methanol by feeding formate so as to create an increasing concentration gradient (transient state). Under particular formate supply conditions, Y could be increased from 0.37 g·g-1 on methanol alone to 0.55 and 0.47 g·g-1 in the presence of formate at dilution rates (D) of 0.045 and 0.075 h-1, respectively. These differences could be explained as being due to a limiting formate consumption rate of 50–60 nmol·min-1·g-1 dry wt., coupled to a net-energy generation independent of D. Any further formate oxidation proceeded without energy gain. Deviations from optimum conditions of biomass increase are discussed in terms of different formate oxidizing systems and uncoupling properties of formate itself. These results are compared to and confirmed by steady-state considerations.