Colonisation and PAH degradation by wood-rotting fungi in contaminated soil

Bioremediation of soils is considered a low-cost alternative to other remediation techniques. Its ability to remove a number of different pollutants has been demonstrated, relying mainly on the activities of indigenous soil bacteria. The polycyclic aromatic hydrocarbons (PAHs) are considered major environmental pollutants in soil, some of them being toxic and others carcinogenic. Since high-molecular-weight PAHs in soil have been shown to be difficult for bacteria to degrade, new techniques for degrading them have been sought. One possibility is that of using wood-rotting fungi. These are able to produce oxidative enzymes, which act outside the cell. Thus far, most studies of bioremediation by use of fungi have focused on pollutant degradation. However, successful development of this technique requires that other matters be taken into consideration as well, including fungal colonisation of the soil and effects of the fungi on indigenous soil microorganisms. One objective of the work reported in the thesis was to investigate the PAH degradation and transformation performance of several wood-rotting fungi in contaminated soil. Inoculation of artificially PAH-contaminated soil with the white-rot fungi <i>Phanerochaete</i> <i>chrysosporium,</i> <i>Pleurotus</i> <i>ostreatus,</i> <i>Pleurotus</i> <i>sajor-caju</i> and <i>Trametes</i> <i>versicolor</i> was found to result in a high degree of PAH removal, indicating the capacity of these fungi to degrade PAHs in a soil environment. The ability of the fungi to bring about the accumulation of PAH metabolites in soil was found to differ considerably between fungal species. Both <i>P.</i> <i>chrysosporium</i> and the two <i>Pleurotus</i> species produced large amounts of 9,10-anthracenedione from parent anthracene when inoculated into artificially contaminated soil. In autoclaved soil inoculated with <i>P.</i> <i>chrysosporium</i> no degradation of the accumulated dione was noted, whereas in non-autoclaved soil treated with this fungus degradation occured. This indicates that, for a complete degradation of PAHs in soil to take place, active indigenous soil microflora is needed. Another aspect of the work focused on the growth of the fungi in contaminated soil. It was found that the capability of the tested fungi to colonise PAH-contaminated soils depends both on the soil origin and the fungal species employed. Whereas artificially contaminated soil supported the growth of all the fungi tested, soil from former gasworks sites caused problems for some of the fungi. The growth of the wood-rotting fungi in the soil and the effect of the fungi on the indigenous soil microorganisms could be assessed by analysing the soil levels of specific phospholipid fatty acids. In doing this, a large negative effect on the soil bacteria could be observed when the soil was inoculated with the highly competitive <i>P.</i> <i>ostreatus</i>. Further investigations showed that the culturable phenanthrene-degrading bacteria were also reduced in number, suggesting the indigenous soil microorganisms to have been hindered in their degradation of <i>P.</i> <i>ostreatus</i>-produced PAH metabolites. Finally, the three-dimensional outgrowth of the brown-rot fungus <i>Antrodia</i> <i>vaillantii</i> in coal-tar-contaminated soil was revealed in lab-scale systems by means of a simple monitoring technique, which was developed. This fungus also was found to be capable of the extensive colonisation of contaminated soil under outdoor conditions.