EFFECT OF TEMPERATURE, HYDROGEN ION AND CERTAIN GROWTH SUBSTRATES ON THE ACTIVITY OF THE CELLULOLYTIC ENZYME COMPLEX IN SELECTED MARINE FUNGI

Halosphaeria mediosetigera and Culcitalna achraspora have been studied
to elucidate the mechanism by which they degrade cellulosic materials in
the sea. H. mediosetigera (700 LC 1), a C1-less variant, was also employed
in this work. Standardized shake-cultures were grown on cellulose and
cellulose derivatives supplemented with NH4N03, tris(hydroxymethyl)aminomethane
and yeast extract in artificial sea water (Lyman and Fleming), pH 7.5, at
25 C. Induced C1 and Cx enzyme and cellobiase activities were determined
calorimetrically by correlation with cotton fiber weight loss, by the
formation of reducing sugars from carboxymethylcellulose and by Glucostat,
respectively. Optimum pH values for both Cx enzyme and cellobiase of
C. achraspora were 6.0 at 37 C while those for H. mediosetigera (700 LC 1)
were 5.0 and 6.0, respectively, at 37 C. In both cultures, Cx enzymes
had a variable optimum temperature ( 37-50 C) at pH 6.0, depending on the
length of the incubation period, while cellobiases had the same optimum
temperature (50 C) at pH 6.0. Thermostability observations on Cx enzyme
and cellobiase of C. achraspora showed almost complete deactivation at
100 C in 15 min for the former and 50 C in 15 min for the latter. Thermostability observations on Cx enzyme and cellobiase of H. mediosetigera
(700 LC 1) showed almost complete deactivation at 45 C in 15 min for the
former and at 50 C in 15 min for the latter. Data indicate that at least
three enzymatic functions are involved in cellulose breakdown by these
cultures.