The effect of diphenylamine on carotenoid, sterol and fatty acid synthesis in Phycomyces blakesleeanus

Physiological characterization of polyextremotolerant yeasts from cold environments of Patagonia

Yeasts from cold environments have a wide range of strategies to prevent the negative effects of extreme conditions, including the production of metabolites of biotechnological interest. We investigated the growth profile and production of metabolites in yeast species isolated from cold environments. Thirty-eight strains were tested for their ability to grow at different temperatures (5-30 °C) and solute concentrations (3-12.5% NaCl and 50% glucose). All strains tested were able to grow at 5 °C, and 77% were able to grow with 5% NaCl at 18 °C. We were able to group strains based on different physicochemical/lifestyle profiles such as polyextremotolerant, osmotolerant, psychrotolerant, or psychrophilic. Five strains were selected to study biomass and metabolite production (glycerol, trehalose, ergosterol, and mycosporines). These analyses revealed that the accumulation pattern of trehalose and ergosterol was related to each lifestyle profile. Also, our findings would suggest that mycosporines does not have a role as an osmolyte. Non-conventional fermentative yeasts such as Phaffia tasmanica and Saccharomyces eubayanus may be of interest for trehalose production. This work contributes to the knowledge of non-conventional yeasts with biotechnological application from cold environments, including their growth profile, metabolites, and biomass production under different conditions.

The role of carotenoids in preventing oxidative damage in the pigmented yeast, Rhodotorula mucilaginosa

Rhodotorula mucilaginosa is an obligate aerobic yeast which contains a high concentration of carotenoid pigment. To test whether carotenoids are able to protect R. mucilaginosa against oxidative injury, yeast cells in liquid culture were incubated with duroquinone (DQ) (100 microM), a redox-cycling quinone known to generate intracellular O2-. or were grown in a hyperoxic atmosphere (80% O2) under conditions where carotenoid concentrations were altered either intracellularly or extracellularly. Neither of these oxidative challenges affected cell growth unless carotenogenesis was blocked by the addition of diphenylamine (50 microM). In the diphenylamine-treated nonpigmented cells, growth was completely inhibited by DQ and by hyperoxia. In normoxia, however, diphenylamine alone reduced growth by only 30%. The growth inhibition observed in diphenylamine-treated cells exposed to hyperoxia was primarily mycocidal rather than mycostatic since plating of these cells onto solid media revealed that only 25% of the cells were viable after 50 h of incubation when compared to plated control cells. Addition of 10 microM beta-carotene to diphenylamine-treated cells completely prevented the growth inhibition caused by either hyperoxia or DQ. Carotenoids, therefore, are able to prevent oxidant-induced cytotoxicity in R. mucilaginosa. Analysis of the absorption spectra of chloroform extracts of beta-carotene-supplemented cells showed that beta-carotene, not the endogenous carotenoid, torularhodin, was the major carotenoid present in these cells. Superoxide dismutase (SOD) activity in R. mucilaginosa was compared with that of another yeast, Saccharomyces cerevisiae by two methods: (i) activity staining of proteins separated by gel electrophoresis and (ii) measurement of inhibition of ferricytochrome c reduction. By these techniques, the R. mucilaginosa SOD activity had the characteristics of Mn-SOD. No Cu/ZnSOD activity was detected. Thus, the apparent absence of Cu/ZnSOD may make the antioxidant capability of endogenous carotenoids even more critical in preventing oxidative damage in R. mucilaginosa.

Carotene-superproducing strains of Phycomyces

Production of beta-carotene by wild-type Phycomyces blakesleeanus can be stimulated by light, chemicals, regulatory mutations, and sexual interaction between mycelia of opposite sex. Through genetic manipulations, we have isolated strains which have simultaneously and constitutively incorporated several of these stimulatory effects. In the dark and in a simple medium, some of the strains produce up to 25 mg of beta-carotene per g (dry weight), or about 500 times the wild-type production under the same conditions. High lycopene-producing strains have also been isolated by using carR mutants, which are blocked in the conversion of lycopene to beta-carotene. These strains should be useful in both industrial production of these pigments and basic research related to carotenogenesis.

Chemical alteration of carotene biosynthesis in Phycomyces blakesleeanus and mutants

The effects of diphenylamine, dimethyl sulfoxide, streptomycin, AMO-1618, and beta-ionone on the carotene composition of a wild-type and three mutant strains of Phycomyces blakesleeanus have been examined. Diphenylamine increased the phytoene and phytofluene concentrations of all strains while reducing the levels of the color carotenes. Dimethyl sulfoxide reduced the concentration of both cyclic and acyclic carotenes, whereas AMO-1618 increased the levels of all carotenes in all the strains. The wild type and mutants responded differently to the presence of streptomycin and beta-ionone. The possible mode of action of the above agents on carotenoid biosynthesis is discussed.

Inhibition of vitamin K2 and carotenoid synthesis in Staphylococcus aureus by diphenylamine

Diphenylamine at concentrations which did not effect the growth rate inhibited the synthesis of vitamin K(2) in both anaerobic and aerobic cultures by about 50%. At this concentration, diphenylamine inhibited the synthesis of the cyclic carotenoids delta-carotene and the rubixanthins 25 to 35% anaerobically and 60 to 90% aerobically. The inhibition of synthesis of cyclic carotenoids and vitamin K(2) by diphenylamine had no detectable effect on the formation of the membrane-bound electron transport system.