New search for pectolytic yeasts.

A new screening method for pectin-depolymerizing microorganisms is described. The method is based on precipitation of non-hydrolyzed citrus pectin with hexadecyltrimethylammonium bromide in a medium solidified with a bacterial gelling gum. A substrate depolymerized by the secreted enzymes does not precipitate, and the positive strains thus show transparent areas around the colonies. The method was used to screen 300 yeast and yeast-like microorganisms belonging to 52 different genera. The secretion of pectin-depolymerizing enzymes occurred with different frequencies in 13 genera (69 positive strains of 207 tested), the lowest frequency being found in the genus Candida (13 positive out of 125 strains tested) and the highest frequency in the genera Aureobasidium (4 of 6) Cryptococcus (29 of 38), Geotrichum (4 of 9), Kluyveromyces (5 of 5), Rhodosporidium (2 of 2), Leucosporidium (2 of 2), Trichosporon (3 of 6) and Ustilago (2 of 2). Strains giving the highest number of harvested cells after growth on pectin in a liquid medium have been identified.