DETECTION OF ENDOGENOUS BETA-GLUCURONIDASE ACTIVITY IN ASPERGILLUS-NIGER

An endogenous beta-glucuronidase that hydrolyses the chromogenic subst rate 5-bromo-4-chloro-3-indolyl-beta-D-glucuronide (X-gluc) in Aspergi llus niger is reported. The activity was induced when the fungus was g rown in media containing xylan, but was either very low, or absent, wh en grown on glucose, Endogenous beta-glucuronidase was primarily locat ed in newly formed hyphae, and was apparent at pH values between 3 and 6. Hydrolysis of X-gluc was sensitive to the inhibitor D-saccharic ac id 1,4-lactone and was irreversibly inactivated by heating. The bacter ial uidA beta-glucuronidase reporter gene was strongly expressed in th e hyphae of transformed A. niger but, in contrast to the endogenous ac tivity, the enzyme was also active at pH 7-8.5. Histochemical localiza tion of uidA expression in A. niger, without interference from the end ogenous beta-glucuronidase activity, was achieved by staining at this pH.