C. sonorensis readily ferments glucose to ethanol, utilizes several
carbon sources other than glucose, and is tolerant to acidic conditions. C.
sonorensis was engineered for lactate production by individually expressing
different lactate dehydrogenase genes in pyruvate decarboxylase positive and
negative strain backgrounds to generate strains with distinctive
characteristics. Production of lactate and ethanol from glucose was strongly
affected by the deletions of the two pyruvate decarboxylase genes PDC1 and
PDC2, the properties of the LDH enzymes, and by LDH enzyme activity which
varied with LDH gene copy number. C. sonorensis LDH strains were also shown
to ferment xylose to lactic acid efficiently via the endogenous xylose
pathway enzymes, e.g. via xylose reductase and xylitol dehydrogenase. An
alternative xylose fermentation pathway was introduced into C. sonorensis by
expressing the XYLA gene from Piromyces sp. encoding xylose isomerase, and
xylose was also shown to be metabolized via this pathway. Co-expression of
the XKS1 gene from Saccharomyces cerevisiae encoding xylulokinase with the
XYLA gene enhanced fermentation relative to expression of XYLA alone.
Deletion of the endogenous reductase and xylitol dehydrogenase genes from a
strain expressing xylose isomerase had a positive effect on lactate
production from xylose.
|Conference||3rd European Federation of Biotechnology Conference |
|Period||13/06/07 → 16/06/07|