Global transcription engineering of brewer's yeast enhances the fermentation performance under high-gravity conditions.

Global transcription engineering was developed as a tool to reprogram gene transcription for eliciting new phenotypes important for technological applications (Science 2006, 314(5805):1565-1568). A recent report indicated that the beneficial growth advantage of yeast cells expressing the SPT15-300 mutation is the result of enhanced uptake and/or improved utilization of leucine and thus was seen only on defined media with low concentrations of leucine (Appl Environ Microbiol 2009, 75(19):6055-6061). Further investigation towards a leucine-prototrophic strain of industrial lager brewer's yeast indicated that integration one copy of SPT15-300 in SPT15 allele, however, did lead to an increased ethanol tolerance on complex rich medium at high gravity fermentation condition. Under brewing conditions, the SPT15-300 mutant produced 80.78 g/L ethanol from 200 g/L carbohydrates after 384 h, almost twice as much as that of the wild-type strain. The results convinced us that the effect of global regulator modification of yeast is at multi-genes level and is extremely complicated.