Proton extrusion and attendant transport phenomena in Candida utilis induced by ethanol

The influence of pH on growth kinetics of yeasts in the presence of benzoate as a sole carbon source

The inhibitory effect and substrate properties of benzoic acid were estimated for 25 yeast strains belonging to genera Candida, Hansenula, Hypopichia, Rhodosporidium, Rhodotorula, Saitoella and Trichosporon. Benzoic acid can serve as a sole carbon source for growth of yeasts belong to genera Rhodotorula, Rhodosporidium and Saitoella in synthetic mineral media. Specific growth rate is strongly dependent both on the concentration of benzoate and the pH value of the cultivation media. Maximum specific growth rate on benzoate is observed in alkaline cultivation media at pH 7.0-7.5 whereas those for growth on glucose in mildly acidic media at pH 5.0. Some of the strains showed weak growth on benzoate even at pH 8.5. Some carotenoid-containing yeasts of the genera Rhodotorula and Rhodosporidium lost their ability to synthesize carotenoid pigments during growth in alkaline benzoate media.

External conditions influencing ethanol oxidation by resting cells of Candida utilis

Effects of ethanol inhibition, initial pH and buffering capacity of media on the catabolic activity of nongrowing cells of Candida utilis were studied. Effects of external conditions on the kinetic of ethanol oxidation and cell respiration are described by mathematical models. The results revealed a significant influence of both the external pH and the buffering capacity of the medium on the kinetic parameters of catabolic activity. The inhibitory effect results in the bottleneck of one of the reaction of the citrate cycle, glyoxylate cycle or electron transfer in a respiratory chain although the total rate of ethanol dissimilation increases under these conditions.

Phenomenological theory of substrate-induced acidification with application to Candida utilis dissimilating ethanol

The mathematical theory of substrate-induced acidification by microorganisms was based on special formulation of mass and charge conservation laws for distinct species. The strength of the theory was tested on the ethanol-induced acidification by Candida utilis in pure water and in phthalate buffer. We showed that the theory may be used to approximate, extrapolate and predict the course of apparent acidification including the effects of buffering capacity of the broth. It makes it possible to formulate mathematical models that are suitable for process simulation and computer control of bioreactors when pH is used as a state variable.

Effect of external pH on acidification and excretion of ethanol intermediates by Candida utilis

External pH affects the acidification induced by ethanol. The apparent specific rate of acidification depends on the dissociation properties and production of carbon dioxide, acetic and lactic acid which are intermediates of ethanol oxidation. The organic acids are transported by Nernst-Einstein diffusion. We designed and identified a new and simple mathematical model that allows us to describe the effect of external pH on nonstationary transport of dissociated intermediates of ethanol oxidation.