Biochemical Studies on the Degradation of Aldonic Acids in Fungi

Abstract

Twenty filamentous fungi were screened for their abilities to grow on D-galactose and degrade D-galactonate and D­ glucortate at pH 3.0 and 5.0 by cell-free extracts ofD-galactose­ grown mycelia. Most of the fungal strains grew fairly on D­ galactose for different incubation periods. Results indicated that the highest rate of degradation was obtained when D-galactonate at pH 3.0 was used as substrate for the Aspergilli namely Aspergillus niger, A.oryzae, A.tamarii, Ajischeri, A.stellatus and A.cameus. The filamentous fungus A.niger was then selected for further detailed studies to demonstrate the possibility of the presence of a catabolic pathway for D-galactose and/or D­ galactonate- degradation in cell-free extracts of thisfungus and the enzymes responsible for this degradation. A lag period of 48 hours was recorded for the growth ofA.niger on the modified Czapek­ Dox's medium containing 30 g./1 ofD-galactose or D-galactonate as the only carbon source for growth.