Effect of temperature on growth of psychrophilic and psychrotrophic members of Rhodotorula aurantiaca

The thermo-dependence of growth kinetic parameters was investigated for the Antarctic psychrophilic strain Rhodotorula aurantiaca and a psychrotrophic strain of the same species isolated in Belgium (Ardennes area). Cell production, maximum growth rate (mu max), and half-saturation constant for glucose uptake (Ks) of both yeasts were temperature dependent. For the two yeasts, a maximum cell production was observed at about 0 degree C, and cell production decreased when temperature increased. The mu max values for both strains increased with temperature up to a maximum of 10 degrees C for the psychrophilic strain and 17 degrees C for the psychrotrophic strain. For both yeasts, Ks for glucose was relatively constant at low temperatures. It increased at temperatures above 10 degrees C for the psychrophilic strain and 17 degrees C for the psychrotrophic strain. Although its glucose affinity was lower, the psychrotrophic strain grew more rapidly than the psychrophilic one. The difference in growth rate and substrate affinity was related to the origin of the strain and the adaptation strategy of R. aurantiaca to environmental conditions.

Cyclosporin C is the main antifungal compound produced by Acremonium luzulae

A strain of Acremonium luzulae (Fuckel) W. Gams was selected in screening new microorganisms for biological control of fruit postharvest diseases, especially gray and blue mold diseases on apples and strawberries. This strain manifests a very strong activity against a large number of phytopathogenic fungi. In this work, the product responsible for this antifungal activity was isolated from modified Sabouraud dextrose broth cultures of A. luzulae. It was purified to homogeneity by reverse-phase column chromatography. On the basis of UV, infrared, and 1H and 13C nuclear magnetic resonance spectra, mass spectral analysis, and the amino acid composition of the acid hydrolysates, the antibiotic was determined to be cyclosporin C. Cyclosporin C showed a broad-spectrum activity against filamentous phytopathogenic fungi but no activity against bacteria or yeasts. Its antifungal activity is only fungistatic. In contrast to Tolypocladium inflatum, another cyclosporin-producing strain, A. luzulae, did not produce additional cyclosporins. This was confirmed by in vivo-directed biosynthesis.