PHYSIOLOGICAL OPTIMIZATION OF SECRETED PROTEIN-PRODUCTION ASPERGILLUS-NIGER

Physiological factors affecting hen eggwhite lysozyme and native gluco amylase production by Aspergillus niger have been examined in batch cu lture. Expression of the genes encoding both proteins was controlled b y the glucoamylase promoter. In standard expression medium (ACMS/N/P), secreted lysozyme yields were found to be maximal at 20-25 degrees C (8-10 mg l(-1)) and markedly reduced at 30-37 degrees C (3-5 mg l(-1)) . Production of lysozyme exhibited similar induction or repression pro files to that of endogenous glucoamylase such that secreted lysozyme y ields could be ordered with respect to growth on the following carbon sources: soluble starch > maltose > glucose > > xylose. Significantly higher yields of up to 30-60 mg l(-1) were obtained in a richer medium containing soya milk, although in contrast to growth in ACMS/N/P, the highest levels of secreted lysozyme were achieved at 37 degrees C. Th is improvement is attributed partly to an increase in culture biomass concentration and to a reduction in medium acidification. Growth in th is medium produced a markedly different pellet morphology.