Effect of raised temperature on the developmental cycle of Candida utilis yeasts

The effect of the submaximal temperature (41.5 degrees C) on growth was studied with a synchronous periodic yeast culture. If the cells were subjected to the action of elevated temperature at the beginning of the growth cycle, the formation of buds was not inhibited in contrast to the separation of nuclei between the daughter and parent cells. If the cells started their growth cycle at the optimal temperature of 32 degrees C and, after spending 0.6 of the cycle at this temperature, were subjected to a temperature of 41.5 degrees C, the separation of nuclei between the daughter and parent cells took place, but the cells were not entirely separated one from another.     

Competition for glucose between the yeasts Saccharomyces cerevisiae and Candida utilis.

The competition between the yeasts Saccharomyces cerevisiae CBS 8066 and Candida utilis CBS 621 for glucose was studied in sugar-limited chemostat cultures. Under aerobic conditions, C. utilis always successfully completed against S. cerevisiae. Only under anaerobic conditions did S. cerevisiae become the dominant species. The rationale behind these observations probably is that under aerobic glucose-limited conditions, high-affinity glucose/proton symporters are present in C. utilis, whereas in S. cerevisiae, glucose transport occurs via facilitated diffusion with low-affinity carriers. Our results explain the frequent occurrence of infections by Crabtree-negative yeasts during bakers' yeast production.     

Extended culture: The growth of Candida utilis at controlled acetate concentrations

Extended culture, a special type of semicontinuous culture, permits prolonged maintenance of a constant or programmed environment in a growing culture by a controlled addition of one or more substrates. Differences between extended culture and continuous culture data are a measure of differences in the properties of cell populations with different cell age distributions but identical steady-state environments. Both extended culture and continuous culture were used to study the growth kinetics of Candida utilis (ATCC 9226) under conditions of substrate inhibition at controlled concentrations of sodium acetate in a carbon-limited mineral salts medium supplemented with 0.01 g/1 yeast extract. Acetate concentrations ranged from 1.2 g/l to 10.8 g/l (expressed as acetic acid), while yeast concentrations varied from 0.3 to 7.8 (g dry cells)/1. Rate parameters such as growth yields (Y), specific growth rates (μ), and linear growth rates (K), were calculated by computer from the data and theory presented herein. Specific growth rates as high as 0.54/hr were observed, although extended culture growth was more nearly linear than exponential in these experiments. Growth yields usually varied between 0.2 and 0.4 (g dry cells)/(g acetate), although values were as high as 0.8 for a brief period during one experiment. Growth yields at a given acetate concentration were correlated by an equation of the form 1/Y = 1/Y_G + m/μ. A maintenance coefficient (m) of 0.17 (g acetate)/(g dry cell-hr) was observed at acetate concentrations of 4.5 and 10. g/1. A typical maximum growth yield (Y_G) of 0.51 (g dry cell)/(g acetate) was obtained at 4.5 g/1 acetate, but an unusually high Y_G of 1.33 was found at 10. g/1 acetate. Oxygen uptake measurements are compared with these cell yield measurements. Linear growth rates in expended culture were correlated by the equation K = 0.89–0.70 (S/S₀) where K has units of (g dry cell)/(l-hr), S is the instantaneous acetate concentration, and S₀ is the initial acetate concentration. The extended culture kinetic data are shown to be substantially different from continuous culture kinetic data. Reason for these differences are discussed in light of diffrences in the cell age distributions, as well as possible differences in experimental conditions.     

Evaluation of on-line viable biomass measurements during fermentations of Candida utilis

In this article the suitability of the Biomass Monitor for on-line measurement of viable biomass is thoroughly evaluated during aerobic fermentations of Candida utilis. Successively a number of specifications of the measuring device are discussed for the studied biological system. The optimal measurement frequency for the given experimental conditions is determined. Furthermore, reliable calibrations of the capacitance readings versus well-known off-line analysis of dry weight and plate counts of the yeast have been established. In addition, the impact of varying fermentation conditions such as stirrer speed and air flow rate together with the influence of the oxygen concentration and conductance of the medium on the capacitance signal have been studied and quantified when a significant influence was observed. It is illustrated that knowledge of the viable biomass during fermentations is very useful in the estimation of the specific growth rate of the organism.     

Isoenzymes of transaldolase in strains of Candida utilis and effect of different growth conditions

The isozymes of transaldolase have been investigated in six strains of Candida utilis. Four of these strains were cloned and in three of them more than one isozyme was found, indicating that mutltiple forms of the activity are present in the same cell. Cloned cells of one strain (C0U) were grown on three different media (YED, 1% dextrose, 1% yeast extract; YEX, 1% xylose, 1% yeast extract; AM, 1% dextrose, 1% ammonium sulfate, 0.025% yeast extract plus mineral salts) and analyzed for transaldolase isozyme patterns. Without autolysis the homogenates showed identical profiles with a single peak of activity characteristic of isozyme I. In spite of significantly different levels of pentose-phosphate pathway metabolites expected these patterns were not appreciably altered. Our data reveal a characteristic pattern for each strain and do not indicate a ready alteration of transaldolase isozymes as a response to changes in nutritional conditions.     

Protein and antigenic spectrum of different species of yeasts of the genus Candida]

The methods of electrophoresis in polyacrylamide gel, immunoelectrophoresis and immunoprecipitation were applied to the study of the protein and antigenic spectra of different species of Candida yeasts. It was revealed that for the majority of the yeast species the prevalence of proteins of definite fractions was characteristic. C. albincans displayed a marked (in comparison with the nonpathogenic species) content of proteins of proteins of group b. The most pronounced antigenic properties in C. albicans and C. tropicalis were possessed by the proteins of the basic character. C. albicans and C. tropicalis yeasts were characterized by similar antigenic spectra, whereas the C. crusei species showed the least affinity with the C. albicans.     

Continuous cultivation of the yeast Candida utilis at different dilution rates on pineapple cannery effluent

Candida utilis was grown on a pineapple cannery effluent in a chemostat at dilution rates ranging between 0.05 and 0.65 h^–1 to establish optimal conditions for biomass production and chemical oxygen demand (COD) reduction. Sucrose, fructose and glucose were the main sugars in the effluent. Maximum value for cell yield coefficient and productivity were (0.686, g_x/g_s) and (2.96, g_x/l/h) at a dilution rate of 0.425 and 0.475 h^–1, respectively, while maximum COD reduction (98%) was attained at a dilution rate of 0.1 h^–1. The maintenance coefficient attained a value of (0.093, g_s/g_x/h). An increase in dilution rate produced a higher protein content of the biomass.     

Inhibition of the growth of Candida utilis by certain heavy metals

The effect of Zn2+, Mn2+, Cd2+ and Hg2+ ions on the kinetics of growth was studied with Candida utilis. The inhibition of Candida utilis growth by Zn2+ and Mn2+ ions is described by the equation for noncompetitive inhibition of enzymatic reactions which is not the case with Cd2+ and Hg2+ ions. The inhibition constants (Ki) for these metals have been determined.     

Continuous fermenter growth of a methionine-overproducing mutant of Candida utilis

Summary An ethionine resistant mutant of Candida utilis was found to maintain an expanded intracellular pool of free l-methionine in batch and continuous cultures. During glucose-limited growth in mineral salts medium in a continuous fermenter, the free l-methionine pool of the mutant was 40–80% higher than in batch cultures, and varied in the range of 25–30 moles/g dry cells (3.7–4.5 mg/g dry cells).     

Continuous growth kinetics of Candida utilis in pineapple cannery effluent

Candida utilis was grown on a pineapple cannery effluent as the sole carbon and energy source in a chemostat at dilution rates between 0.10 and 0.62 h(-1) to determine the growth kinetics. The principal sugars in the effluent were sucrose, glucose, and fructose. The cell yield coefficient on carbohydrate varied with dilution rate and a maximum value of 0.63 was observed at a dilution rate of 0.33 h(-1). The steady-state concentrations of carbohydrate, reducing sugar, and chemical oxygen demand (COD) appeared to follow Monod saturation kinetics with increasing dilution rate, although none of the measured parameters represented a pure substrate. The maximum specific growth rate and reducing sugar saturation constant were 0.64 h(-1) and 0.060 g/L, respectively. A maximum cell mass productivity of 2.3 g/L h was observed at a dilution rate of 0.51 h(-1). At this dilution rate, only 68% of the COD was removed. A 95% COD removal was attained at a dilution rate of 0.10 h(-1). Optimal yeast productivity and COD reduction occurred at a dilution rate of 0.33 h(-1).