A number of yeast strains, isolated from sugar cane mills and identified as strains of Kluyveromyces
marxianus var. marxianus, were examined for their ability to ferment glucose and cane syrup to ethanol at high
temperatures. Several strains were capable of rapid fermentation at temperatures up to 47°C. At 43°C, >6%
(wt/vol) ethanol was produced after 12 to 14 h of fermentation, concurrent with retention of high cell viability
(>80%). Although the type strain (CBS 712) of K. marxianus var. marxianus produced up to 6% (wt/vol)
ethanol at 43°C, cell viability was low, 30 to 50%, and the fermentation time was 24 to 30 h. On the basis of
currently available strains, we suggest that it may be possible by genetic engineering to construct yeasts capable
of fermenting carbohydrates at temperatures close to 50°C to produce 10 to 15% (wt/vol) ethanol in 12 to 18
h with retention of cell viability