Development of a strain of Hansenula polymorpha for the efficient expression of guar α‐galactosidase

Abstract

A strain of the methylotrophic yeast Hansenula polymorpha, A16 has been developed that expresses the guar α‐galactosidase gene to 22.4 mg/g dry cell weight in chemostat cultures at a dilution rate of 0.1 h⁻¹. This corresponds to more than 13.1% of solube cell protein, of which 56–62% is secreted into the medium. The α‐galactosidase gene was flanked by the promoter and terminator sequences of the H. polymorpha mox gene, which can direct expression of the mox gene itself more than 30% of total cell protein under methanol growth. The expression cassette (pUR3510) based on the Saccharomyces cerevisiae plasmid, YEp13, was integrated into the genome. Such transformants were stable in chemostat cultures and exhibited 100% stability for both α‐galactosidase⁺ and leu⁺ phenotypes. Chemostat cultures produced higher levels of α‐galactosidase with higher specific productive expressed as mg α‐galactosidase g⁻¹ h⁻¹ compared to batch cultures.