PRODUCTION OF PECTIN-DEGRADING ENZYMES BY ERICOID MYCORRHIZAL FUNGI

Production of enzymes which degrade plant cell wall macromolecules has been studied in relatively few ericoid fungal isolates, although thes e polymers are a major component of the organic litter and an importan t source of nutrients for these fungi. Our aims were to investigate wh ether the ability to degrade the wall pectic component, only reported for one isolate, is a general feature of ericoid fungi. Of about 35 is olates from different geographic regions, all were capable of growing on pectin as the sole carbon source. Polygalacturonase (PG) activity w as detected to a different degree in the culture filtrates and indepen dently of the fungal growth rate. Solid and liquid isoelectric focusin g allowed separation and identification of several polygalacturonase i soforms. Among the fungal isolates investigated, those from the northe rn hemisphere produced mostly acidic isoforms, whereas isolates from S outh Africa secreted more abundantly basic isoforms. However, purifica tion and biochemical characterization of several PG isoforms from the different isolates revealed an optimal activity in the acidic pH range for all the PG enzymes tested. Polygalacturonase enzymes seem to be a n important component of the enzymatic arsenal secreted by ericoid fun gi during their saprotrophic life. In addition, they could also play a role during root colonization, since penetration across the plant cel l wall is a prerequisite for the establishment of endomycorrhizal symb iosis.