Study on the protoplast fusion between a thermotolerant yeast and Saccharomyces cerevisiae

Intergenetic protoplast fusion between Saccharomyces cerevisiae 396 and thermotolerant yeast Candida sp. C6 has been studied. 396 is a molasses distiller's yeast, and C6 which was isolated from the hot spring in Yunnan, grows well at 45 degrees C. The auxotrophic mutants of 396 (Arg.) and C6 (Lys.) were obtained by treatment of NTG. The fusion frequency was 0.91 per 10(5) protoplasts. Six fusants were studied, the average size of their cells is 1.3 times the size of their parents, while the DNA content is 1.6 times. Other characteristics of the fusants including colonial and cell morphology, physiology, especially in carbon sources assimilation appeared different. The possibility of heterokaryon formation was excluded except for F2 and F14. The growth curves, efficiency of sugar utilization and ethanol yield of original parents 396 and C6, immediate parents 396 (Arg.) and C6 (Lys.), fusants F1, F7, F12 and F13 have been compared at 28 degrees C, 40 degrees C and 45 degrees C. The intergenetic fusant F13 with efficiency of substrate utilization 94.3% and the final ethanol concentration 59.7 g/l at 40 degrees C has been selected.