Differential glucoamylase expression in Schwanniomyces castellii induced by maltose

Abstract

Different levels of glucoamylase expression occurred when Schwanniomyces castellii strain 1402 was shifted during growth on glucose to either glucose, maltose, or soluble starch medium. Extracellular glucoamylase activity was greatest from cells grown on maltose (~22×), slightly less on soluble starch (~16×), and least on glucose (1×). Glucoamylase biosynthesis was further studied by labelling of total proteins in vivo with [35S]methionine and immunoprobing with a polyclonal anti-glucoamylase antibody. Mature active glucoamylase is 146 kDa. Maltose cultures expressed four cellular (75, 78,138, and 146 kDa) and two extracellular (78 and 146 kDa) polypeptides. Neither the 138- nor the 146-kDa products were detected in cells in the presence of glucose; the 78-kDa product is expressed at approximately 5% the level obtained from cells in maltose. The 146-kDa glucoamylase is expressed within 30 min after transfer of cells from glucose- to maltose-containing medium. This expression appears to be cell growth and concentration independent and is therefore similar to galactose-inducible enzyme expression in Saccharomyces cerevisiae.