Jacob Martin, Bjarne Bartlett, and Chris Curtin*
*Oregon State University, Department of Food Science and Technology, Wiegand Hall, SW Campus Way, Corvallis, OR, 97331 (christopher.curtin@oregonstate.edu)

Brettanomyces bruxellensis possesses the rare (among yeast) ability to assimilate nitrate, which confers sufficient advantage for it to outcompete Saccharomyces cerevisiae in fermentation processes enriched in nitrate, such as fermentation of sugarcane for bioethanol. When nitrate is abundant, B. bruxellensis can grow and ferment more rapidly under anaerobic conditions, through reversal of the Custers’ effect and concurrent acetate production. Surprisingly, some B. bruxellensis strains cannot use nitrate due to structural gene deletions. Could this be due to lack of advantage in environments with low nitrate concentrations?

Genomes of 189 B. bruxellensis strains were analyzed for the presence/absence of nitrate assimilation genes, with 13 strains displaying at least partial deletion within the structural gene cluster. Previous studies showed loss-of-heterozygosity (LOH) events across this cluster, that may have some effect on phenotype. We found a high proportion of strains with LOH (68%) that varied with regard to the initiation of LOH from 0 to 10 kb upstream of the cluster. We are currently evaluating association of deletion and LOH events with different B. bruxellensis populations, and correlation with growth on nitrate.

To evaluate the relevance of nitrate assimilation during fermentation in low-nitrate environments, one strain that displayed stronger growth on solid medium with nitrate was selected. Preliminary experiments in anaerobic environments show this strain used significantly more glucose (p = 2^e-16) and produced more acetic acid (p = 2^e-16) when grown on nitrate than ammonium, even at relatively low concentrations (0.042 g/L) of nitrogen.

Funding Support: Agricultural Research Foundation