Screening of Diesel Oil Degrading Species of Aspergillus for the Production of Different Enzymes Using Agar Plate Assay Method

We have earlier isolated Aspergillus luchuensis, A. violaceofuscus, A. niveus, A. terreus, A. japonicus and A. ustus from naturally degraded diesel oil in the soils using nutrient rich technique. These species were cultured to produce enzyme complexes on 10% (w/v) diesel oil broth containing 0.5 and 1.0% (w/v) jaggery at 37 and 45℃ temperature separately for 7, 14 and 21 days. It was observed that all 6 species of Aspergillus produced luxuriant mycelial growth at day-7 on both temperatures, however, at 45℃, the liquid broth dried on 14th day of incubation, and therefore, secretory extracellular enzymes produced at 37℃ were screened to test the activities of amylases, gelatinases, lipases, cellulases, pectinases, proteases and manganese peroxidases using agar plate assay method. These enzymes are responsible for beaking down different bonds of the complex hydrocarbons. It was found that all 6 test species of Aspergillus produced all 7 enzymes at higher concentration at day 21 on diesel oil containing 1.0% jaggery. The production of enzyme increased with increasing period of incubation from day 7 to day 21. A. luchuensis produced highest activities of proteases, A. violacefuscus - amylases, A. niveus - gelatinases, A. terreus and A. ustus - pectinases, and A. japonicus produced highest activities of manganese peroxidases. All these enzymes contribute in the degradation of diesel oil in nature. This study revealed that the production of varying amounts of different enzymes by all these 6 species of Aspergillus has significant ecological and bioremediation potential.