Isolation, characterization, and fermentative pattern of a novel thermotolerant Prototheca zopfii var. hydrocarbonea strain producing ethanol and CO2 from glucose at 40 °C
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A novel thermotolerant strain of the achlorophyllous micro-alga Prototheca was isolated from a hot spring. The isolate was found to produce an appreciable amount of ethanol and CO2 from glucose under anoxic conditions at both 25 and 40 °C; this type of alcohol fermentation has not yet been reported in the genus Prototheca. Moreover, it also evolved gas from sucrose after a time lag at 40 °C. Its taxonomic characteristics coincided with those of Prototheca zopfii var. hydrocarbonea, and phylogenetic analysis, based on a small-subunit (SSU) rDNA sequence, also revealed a close relationship between the two strains. D-lactic acid, ethanol, CO2 and a trace of acetic acid were produced from glucose, but L-lactic acid, formic acid, and H2 were not. At 25 °C, D-lactic acid and ethanol were produced in approximately equimolar amounts under N2/H2/CO2, whereas ethanol production was predominant under N2. More ethanol was produced at 40 °C than at 25 °C irrespective of the gas composition in the atmosphere. This is the first report on gas production from glucose and on the changes in the fermentative patterns as a function of temperature for the genus Prototheca.
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