Isolation and characterisation of fungi growing on volatile aromatic hydrocarbons as their sole carbon and energy source

Abstract

Five fungal strains that are able to grow on toluene were isolated from enrichment cultures. Three different techniques were used: solid state-like batches, air biofilters and liquid cultures. Fungal growth in the latter systems was favoured by combining low pH and low water activity. Soil and groundwater samples from gasoline-polluted environments were used as inocula. The isolates were identified as deuteromycetes belonging to the genera Cladophialophora, Exophiala and Leptodontium and the ascomycete Pseudeurotium zonatum. The previously isolated toluene-degrading fungus Cladosporium sphaerospermum was included in the present study. Results showed that fungi grew on toluene with doubling times of about 2 to 3 days. Some of the strains also grew on ethylbenzene and styrene. The apparent half-saturation constant (Km) for toluene oxidation ranged from 5 to 22 μM. Degradation activity was inhibited by 50% at toluene concentrations ranging from 2.4 to 4.7 mM. These kinetic parameters are comparable to analogous data reported for toluene-degrading bacteria. The ability of fungi to grow at low water activities and low pH suggest that they may be used for the purification of gas streams containing aromatic hydrocarbons in air biofilters.