Distribution of Dekkera bruxellensis in a sugarcane-based fuel ethanol fermentation plant

We investigated the presence of the yeast Dekkera bruxellensis in samples collected at three points surrounding the industrial alcoholic fermentation plants of two distilleries where there are often cases of contamination caused by this yeast: this involved sugar cane wash water, feeding sugar cane juice and vinasse from the treatment pond. Total yeast was isolated in WLN medium with bromocresol green and cycloheximide and further selected on the basis of its ability to grow in synthetic medium containing nitrate. Following this, colonies were selected from the distribution on nitrate plates and identified by amplification with species-specific primers and DNA sequencing of the 26S-D1/D2 locus. The results showed that D. bruxellensis is introduced through the feeding substrate, which suggests that its cells originated with the harvested cane. Subsequently, its population circulates as a result of the reuse of water for washing the cane, in a continuous re-inoculation of the plant with yeasts. Furthermore, the yeast population is formed in the vinasse by the addition of wash water into the treatment ponds and then reintroduced to the culture fields by fertigation, so that the process can be renewed in the following season. It is now possible to adopt sanitation procedures that can prevent the entry of the contamination to the fermentation process.

The presence of the yeast Dekkera bruxellensis is sometimes attributed to a decline in the industrial productivity of ethanol since it has a more limited fermentation capacity than Saccharomyces cerevisiae. Although its adaptability to the industrial environment has been noted, so far, there has been no evidence to determine the source of this contamination. In this study, we provide evidence to show that D. bruxellensis comes from the fields together with the harvested cane and is then accumulated and recirculated. It might be possible to prevent the accumulation of this yeast by carrying out sanitation controls during the harvesting season.