Biotechnological Importance

At one time, most of the industrial research on hydrocarbon metabolism consisted of attempts to produce yeast single-cell protein from petroleum, which was cheap and widely considered to be surplus (Lindley 1992). Little of that type of research is being done now, but there has been extensive progress on the biotransformation of terpenes for the production of flavors, fragrances, and drug intermediates (Trudgill 1994) and on the degradation of PAHs and other toxic hydrocarbons during the bioremediation of soils (Atlas and Cerniglia 1995).

Many of the hydrocarbons contaminating soils and groundwater near leaking fuel tanks, oil spills, and chemical waste dumps can be degraded by fungi (Atlas and Cerniglia 1995; Cerniglia and Sutherland 2001; Colombo et al. 1996). Most of the recent work in this field has been done on PAHs, but some of it has been on BTEX compounds (Yadav and Reddy 1993) and on alkanes (Nwachukwu 2000). Although gigantic oil spills from marine supertankers and offshore oil wells attract immediate public concern, smaller spills from fuel storage tanks are numerous and usually more amenable to bioremediation (Atlas and Cerniglia 1995). The fungal bioremediation of contaminated soils may be accomplished either by removing soil for off-site treatment (May et al. 1997) or by using organic solvents to extract hydrocarbons from the soil for later degradation (Field et al. 1996). On-site bioremediation may be done with fungi that can grow through the soil mass to reach the PAHs (Cerniglia 1997; Novotny et al. 1999). Since few soil microorganisms have the ability to degrade high-molecular-weight PAHs alone (Juhasz and Naidu 2000), fungi and bacteria are now being added together to achieve bioremediation (Boonchan et al. 2000). Fungi have also been used to remove PAHs from wastewater (Liao et al. 1997) and biofilters containing selected fungi have been used to remove toluene and other hydrocarbons from waste gases (GarcĂ­a-Pena et al. 2001).

Another application of fungal biotechnology is the transformation of renewable resources, such as the terpenes a-pinene, b-pinene, and limonene, to valuable metabolites that are in demand by the flavor and fragrance industries (Prema and Bhattacharyya 1962; Tan et al. 1998; van Dyk et al. 1998). Fungi usually transform monoterpenes to hydroxylated derivatives and ketones. For instance, (+ )-limonene may be hydrated to (+)-a-terpineol, a widely used fragrance chemical (Demyttenaere et al. 2001; Tan et al. 1998), or oxidized to perillyl alcohol, which not only inhibits the growth of some tumor cells but also is a precursor of the artificial sweetener perillaldehyde oxime (de Oliveira and Strapasson 2000). a-Pinene can be oxidized to verbenone, which is used by the flavoring industry (Agrawal and Joseph 2000). Sesquiterpenes are transformed by fungi to a variety of products (Abraham et al. 1992; Miyazawa et al. 1995; 1997; 1998). Other hydrocarbons may be transformed by fungi to intermediates that are useful in the synthesis of pharmaceuticals and biochemicals (Johnson et al. 1973; Uzura et al. 2001).

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