Some aspects of the regulation of nitrogen metabolism in the yeast genus candida. Study of the kineties of ammonium transport to the cells of hydrocarbon oxidizing yeast of the genus candida with a change in nitrogen nutrition

Abstract

In his study the kinetics of the ammonium transport to he hydrocarbon-oxidizing yeast cells and the specific features of its regulation as one of the aspects of catabolite nitrogen repression were investigated. As the objects 3 mesophilic strains of C. maltosu, the thermotolerant strain C. rugosa as well as a collection of the thermotolerant strain C. blunkii BKM-Y-462 type were selected.One of the major objects of industrial biotechnological processes aimed a t producing single-cell protein is the yeast of the genus Candida. The practical value of the products obtained as feedstock for cattle and food for human beings is primarily determined by the protein content in the biomass and its aminoacid composition. The protein content in a product is known to depend on genetic properties of the strain used as well as on the conditions of its cultivation and postfermentation treatment of the biomass. I n spite of the fact that the yeast of the genus Candida has been widely used for a long period of time for obtaining single-cell protein from different kinds of raw materials, the nitrogen metabolism of the yeast involved has been studied insufficiently which prevents the regulation required for the nitrogen metabolism under industrial conditions. The aim of this work has been to study the kinetics of the ammonium transport to the hydrocarbon-oxidizing yeast cells and the specific features of its regulation as one of the aspects of catabolite nitrogen repression. As the objects of this study (Tab. 1) highly productive strains of hydrocarbon oxidizing yeast were selected namely 3 mesophilic strains of C. maltosa, which differ from each other by the level of protein content in the biomass, and the thermotolerant strain C. rugosa, as well as a collection of the thermotolerant strain C. blankii BKM-Y-462 type, which does not oxidize hydrocarbons. Thermotolerant strains are characterized by having the protein content in the biomass a t the level of low-protein mesophilic strains. Previous investigations studying a change of such parameters as the rate of dilution, growth temperature and pH value of the medium have shown that the optimal value of parameters for yeast growth also provides the highest protein content in biomass. When optimal parameters are chosen, the protein content changes to a lesser extent than other nitrogen-containing components of the cell. 5 Acta Biotechnol. 10 (1990) 2

Candida maltosa

“…The yeast C. maltosa is not able to utilize nitrate (N0 3 -) or nitrite (N0 2 -), but it can use ammonium ions (NHt), urea, or amino acids as sole source of nitrogen for growth (Metz and Reuter 1977;Casper et al 1985a,b;Guselnikova et al 1989Guselnikova et al , 1991Gradova et al 1990;Huth et al 1990a,b,c; Table 3). …”

“…Interestingly, this value did not vary significantlywhen using glucose or alkanes as carbon sources (Gradova et al 1983(Gradova et al , 1990. Under nitrogen limitation conditions, the crude protein content (up to 17-23%) and the nucleic acid (3-4%) content of alkane-grown cells decreased strongly, connected with an increase of both lipid (28-30%) and total carbohydrate (38-44%) contents (Bruckner and Troger 1981a,b;Gradova et al 1983).…”

“…With increasing temperature, the yield and protein content decrease, but the degree of decrease is strain-dependent (Gradova et al 1983). In contrast to C. tropicalis and other thermo tolerant yeast (C. albicans, C. rugosa, C. blankii), it cannot grow at 43 DC and higher temperatures (Gradova et al 1983(Gradova et al , 1990Golubev et al 1986). In comparison with the psychrotolerant yeast Y.…”

“…The ammonium assimilation and its regulation in C. maltosa was studied by Popov et al (1980), Casper et al (1985a, Huth et al (1990a,b,c), Gradova et al (1990), and Guselnikova et al (1991). Data on the kinetics of ammonium transport into the cell using methylamine as an analogous material nonmetabolizable by the cells were published by Gradova et al (1990) and Guselnikova et al (1991). After cultivation on ammonium-containing medium, C. maltosa possesses a constitutive and active system for methylamine transport having a Km of2 x lO-4M (low affinity permease) not significantly influenced by the carbon source (glucose or octadecane).…”

“…Normally, different strains contain about 50-60% crude protein (total nitrogen N x 6.25) or 40-45% of true protein according to Lowry on a dry weight basis (Bruckner and Troger 1981a,b;Kolblin and Birkenbeil 1981;Kolblin and Troger 1982;Gradova et al 1983Gradova et al , 1990. This biomass of alkane-grown cells contains further about 25-30% total carbohydrates (polysaccharides as 8-10% high molecular mannan, 3-4% low molecular mannan, 11-15% glucan, mainly localized in the cell walls, 1.5-2% glucogen, and 0.7% trehalose), 6-7% total nucleic acids and 15-18% lipids.…”