Secretion of a Cryptococcus albidus xylanase in Pichia stipitis resulting in a xylan fermenting transformant.

A fragment of cDNA containing the xylanase gene (XLN) of Cryptococcus albidus was inserted into the vector pJHS which contains the selectable marker his3. To permit expression of the XLN gene, the xylose reductase promoter XYL1 from Pichia stipitis was introduced in front of the XLN gene. P. stipitis PJH53, a histidine-dependent strain, transformed with this plasmid produced an active extracellular xylanase. The enzyme secreted by P. stipitis had an apparent molecular mass of 50 kDa, which was slightly greater than that of the native 48-kDa xylanase produced by C. albidus. The expression of the XLN gene in P. stipitis allowed it to use xylan as a carbon source and to ferment xylan directly to ethanol under anaerobic conditions.