A few microorganisms have been shown to utilize four ring PAHs for their growth in the absence of co-factors or surfactants (Weisenfels et al. 1990 ; Walter et al. 1991 ; Boldrin et al. 1993 ; Thibault et al. 1996). However, a Mycobaterium sp., isolated from PAH contaminated freshwater sediments, was found to be capable of mineralizing phenanthrene, pyrene were detected with the nahAc gene probe, indicating that enaymes involed in PAH metabolism were not related to the well characterized naphthalene dioxy genase gene (Churchill et al. 1999)