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Encro <br /> • <br /> ia/insi9 hts <br /> Mycobacterium, Nocardioides, Pseudomonas, Ochrobactrum, and Ralstonia species have been isolated which are capable of aerobic <br /> growth on both ethene and vinyl chloride(see Mattes et al. [49]for a review).The initial steps in the pathway are the monooxygenase <br /> (etnABCD) catalyzed conversion of ethene and vinyl chloride to their respective epoxyalkanes (epoxyethane and chlorooxirane), <br /> followed by epoxyalkane:CoM transferase(etnE)mediated conjugation and breaking of the epoxide[50]. <br /> Aerobic-Chlorinated Benzenes:In general,chlorobenzenes with four or less chlorine groups are susceptible to aerobic biodegra- <br /> dation and can serve as growth-supporting substrates. Toluene dioxygenase (TOD) has a relatively relaxed substrate specificity <br /> and mediates the incorporation of both atoms of oxygen into the aromatic ring of benzene and substituted benzenes (toluene <br /> and chlorobenzene). Comparison of TOD levels in background and source zone samples from a CB-impacted site suggested that <br /> CBs promoted growth of TOD-containing bacteria [51]. In addition, aerobic biodegradation of some trichlorobenzene and even <br /> tetrachlorobenzene isomers is initiated by a group of related trichlorobenzene dioxygenase genes (TCBO). Finally,phenol hydrox- <br /> ylases catalyze the continued oxidation and in some cases, the initial oxidation of a variety of monoaromatic compounds. In an <br /> independent study,significant increases in numbers of bacteria containing PHE genes corresponded to increases in biodegradation <br /> of DCB isomers[51]. <br /> Aerobic-Chlorinated Methanes:Many aerobic methylotrophic bacteria,belonging to diverse genera(Hyphomicrobium,Methylobac- <br /> terium, Methylophilus, Pseudomonas, Paracoccus, and Alibacter) have been isolated which are capable of utilizing dichloromethane <br /> (DCM) as a growth substrate. The DCM metabolic pathway in methylotrophic bacteria is initiated by a dichloromethane dehalo- <br /> genase (DCMA) gene. DCMA is responsible for aerobic biodegradation of dichloromethane by methylotrophs by first producing <br /> formaldehyde which is then further oxidized [52]. As discussed in previous sections, soluble methane monooxygenase (sMMO) <br /> exhibits relaxed specificity and co-oxidizes a broad spectrum of chlorinated hydrocarbons.In addition to chlorinated ethenes,sMMO <br /> has been shown to co-oxidize chloroform in laboratory studies[38,41]. <br /> 14 10515 Research Drive <br /> Knoxville,TN 37932 <br /> Phone: 865.573.8188 <br /> Fax: 865.573.8133 <br /> Web: www.microbe.com <br />