Background: Robust second generation bioethanol processes require
microorganisms able to ferment inhibitory lignocellullosic
hydrolysates. In this study, the inhibitor tolerance and flocculation
characteristics of Saccharomyces cerevisiae CCUG53310 were evaluated
in comparison with S. cerevisiae CBS8066. Results: The flocculating
strain CCUG53310 could rapidly ferment all hexoses in dilute acid
spruce hydrolysate, while CBS8066 was strongly inhibited in this
medium. In synthetic inhibitory media, CCUG53310 was more tolerant to
carboxylic acids and furan aldehydes, but more sensitive than CBS8066
to phenolic compounds. Despite the higher tolerance, the increase in
expression of the YAP1, ATR1 and FLR1 genes, known to confer resistance
to lignocellulose-derived inhibitors, was generally smaller in
CCUG53310 than in CBS8066 in inhibitory media. The flocculation of
CCUG53310 was linked to the expression of FLO8, FLO10 and one or more
of FLO1, FLO5 or FLO9. Flocculation depended on cell wall proteins and
Ca2+ ions, but was almost unaffected by other compounds and pH values
typical for lignocellulosic media. Conclusions: S. cerevisiae CCUG53310
can be characterised as being very robust, with great potential for
industrial fermentation of lignocellulosic hydrolysates relatively low
in phenolic inhibitors