Isolation and characterisation of Geotrichum candidum for extracellular polygalacturonase production.

Fifty microorganisms including seven fungi and 43 bacteria were isolated fr om citrus fruit rot. The iodine test and enzyme activity assay showed pecti nolytic activity in 38 of the selected micro-organisms, this activity being higher in yeasts. The two species that present the highest activity were i dentified as Candida guillermondii and Geotrichum candidum. Geotrichum cand idum produces an extracellular polygalacturonase that is active on pectin a nd on polygalacturonic acid. The enzyme is strongly induced by these two su bstrates, and this induction is glucose-repressible. No activity is detecta ble during culture with simple oses as the sole source of carbon. The biosy nthesis of the enzyme is strongly inhibited by the presence of glucose in c ulture medium. Maximum polygalacturonase activity (reducing-group-releasing activity) is as high as 2,150 mu mole . L-1. min(-1) and is reached after 48 h or growth in a fermentor, at 30 degrees C and pH 5, in the presence of polygalacturonic acid 7.5 g . L-1 and an appropriate nitrogen source.