Bioremediation of an aged polycyclic aromatic hydrocarbons (PAHs)-contaminated soil by filamentous fungi isolated from the soil

Abstract

Twenty-one filamentous fungi were isolated from the soil of an old polycyclic aromatic hydrocarbon (PAH)-contaminated gaswork site and tested in their native soil for PAH degradation. This degradation study was performed for each isolate with two inoculation treatments, by spore or mycelial inoculum. An improvement in the extent of total PAH degradation occurred with mycelial inoculum. The greatest degradation was obtained with Coniothyrium sp. (26.5%) and Fusarium sp. (27.5%) inoculum, especially for PAHs of high-molecular-weight that contained more than three fused aromatic rings. Correlations between mycobiota capacity (in treatments inoculated with mycelium) and PAH characteristics (structure, water solubility, bioavaibility) were obtained from correspondence factorial analysis. This study suggests that such filamentous fungi could be used in clean-up of long-term contamination of soils by PAHs.

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants found in soil at wood preservation plants and gasworks. Because they are genotoxic and carcinogenic, they represent a considerable environmental concern (White 1986; Palhmann and Pelkonen, 1987). As abiotic factors do not contribute significantly to the elimination of PAHs with more than three rings from soil (Cerniglia, 1993), much effort has been expended in examining the contribution of microorganisms to degrade PAHs. Low-molecular-weight PAHs are readily degraded. However, high-molecular-weight PAHs (four and more rings) are more persistent, in part because of their low bioavaibility, due to their strong adsorption onto the soil organic matter (Manilal and Alexander, 1991; Weissenfiels et al., 1992). Soil adsorption is especially strong in long-term contaminated soils, which is often the case of soils in the vicinity of gas manufacturing plants. Therefore, many investigations have focused attention on the microorganisms that show an ability to degrade high-molecular-weight PAHs for cleaning up contaminated sites.

The white rot fungus Phanerochaete chrysosporium features among the PAH degrading microorganisms that have been the most extensively investigated (Sutherland, 1992; Morgan et al., 1993; Field et al., 1995; Paszczynski and Crawford, 1995). These fungi produce extracellular enzymes, including lignin peroxidases [LiP] and manganese peroxidases [MnP] which are presumed to be involved in the PAH degradation process (Augustin and Muncnerova, 1994). Other studies have focused on the ability of non-lignolytic fungi, such as Cunninghamella elegans (Cerniglia and Gibson, 1979; Cerniglia, 1993) and Penicillium janthinellum (Launen et al., 1995) which can also metabolize a variety of PAHs to polar metabolites. PAH degradation by white rot fungi is well documented whereas the knowledge about filamentous fungi is scarce, although these microorganisms are also abundant in heavily contaminated sites (Hofrichter et al., 1993; Sack and Günther, 1993). Therefore, the full potential of biodegradation by filamentous fungi has not been fully investigated for bioremediation purposes. The use of filamentous fungi isolated from PAH contaminated soil may offer advantages for several reasons; particularly (i) since most of them are adapted to this contaminated environment allowing the inoculum to survive and (ii) owing to their abilities to extend through the soil by hyphal elongation, fungi can access xenobiotics (Bennett and Faison, 1997).

The present study was conducted with the following goals: (a) to isolate filamentous fungi from a PAH-contaminated soil, and (b) to evaluate the ability of these fungi in degrading PAHs, especially those of high-molecular-weight, in their native contaminated soil.