Construction
of lactic acid producing sour dough yeast Torulaspora delbrueckii.
Matti Korhola (1),
Marja Aittamaa (1), Richard Degré (2), Hilkka Turakainen (1)
(1) Biosciences, University of Helsinki, Viikinkaari 9, Helsinki, FIN-00014,
Finland (matti.korhola@helsinki.fi); (2) Lallemand Inc., 1620 Prefontaine,
Montreal, Quebec, H1W 2N8 Canada
We have
concentrated our studies on characterization and exploitation of different
yeasts isolated from Finnish rye bread sour doughs. One possibility is to use
the yeasts which naturally function well in their sour environment as hosts for
heterologous lactate dehydrogenase (LDH) gene permitting lactic acid production
in bread leavening or in chemical production. We cloned by PCR the Bacillus
subtilis
LDH gene and put it under ADC1 promoter and terminator control into pAAH5
vector and from there into pJTSK1 vector resulting in plasmid construct pABM91.
The pJTSK1 is a shuttle vector capable of replicating in Escherichia coli,
Saccharomyces cerevisiae and T. delbrueckii. Our results showed that T.
delbrueckii,
transformed with this plasmid construct pABM91, produced about 1 g of lactic
acid / L in 3-5 days when grown aerobically or fermentatively in YPD10 (10 %
glucose). In contrast the same construct in S. cerevisiae resulted in about 20-30
g of lactic acid / L when grown in YPD10 for 24 h in batch culture. In this
case the batch volumetric productivity was about 0.8 g of lactic acid / L / h
and the specific productivity about 0.4 g of lactic acid / g YDM / h, both
about 100-fold higher than in T. delbrueckii. There was of course
concomitant ethanol production. We are currently investigating the reason(s)
for the poor performance of the T. delbrueckii LDH transformants.