Novel Pathway of Toluene Catabolism in the Trichloroethylene-Degrading Bacterium G4

Abstract

Cresol and 3-methylcatechol were identified as successive transitory intermediates of toluene catabolism by the trichloroethylene-degrading bacterium G4. The absence of a toluene dihydrodiol intermediate or toluene dioxygenase and toluene dihydrodiol dehydrogenase activities suggested that G4 catabolizes toluene by a unique pathway. Formation of a hybrid species of 180-and '60-labeled 3-methylcatechol from toluene in an atmosphere of 1802 and 1602 established that G4 catabolizes toluene by successive monooxygenations at the ortho and meta positions. Detection of trace amounts of 4-methylcatechol from toluene catabolism suggested that the initial hydroxylation of toluene was not exclusively at the ortho position. Further catabolism of 3-methylcatechol was found to proceed via catechol-2,3-dioxygenase and hydroxymuconic semialdehyde hydrolase activities.

Aerobic biodegradation of N‐nitrosodimethylamine (NDMA) by axenic bacterial strains

“…JS150 is unusual in that it appears to have a redundant system that encodes for both the aromatic monooxygenases T4MO and T2MO as well as the more readily expressed toluene dioxygenase; however, expression as determined by metabolic products was primarily demonstrated to be the dioxygenase (Haigler et al, 1992;Olsen, 1995, 1997;Kahng et al, 2001). Figure 2 depicts the variety of initial toluene oxidation reactions catalyzed by the oxygenase-expressing bacteria used in this study (Leahy et al, 1996;Shields et al, 1989).…”

“…A variety of bacteria expressing toluene oxygenases were tested, including both mono-and dioxygenase-expressing cells (Table I). Pseudomonas mendocina KR1 expresses a toluene 4-monooxygenase (T4MO) (Yen et al, 1991); Ralstonia pickettii PKO1 that primarily expresses a T4MO similar to that of KR1 ; Burkholderia cepacia G4 expresses a toluene 2-monooxygenase (T2MO) (Shields et al, 1989); and Pseudomonas putida mt-2 expresses a xylene monooxygenase that is also referred to as a toluene sidechain monooxygenase (TMO) (Worsey and Williams, 1975). Four strains were tested that degrade toluene using 2,3 dioxygenase enzymes (TDO): Pseudomonas sp.…”

“…Interestingly, bacterial oxygenases that are active on donors such as methane, propane, ammonia, and toluene have also been shown to have the ability to oxidize xenobiotic compounds such as chlorinated aliphatic hydrocarbons (Arciero et al, 1989;Nelson et al, 1987;Tsien et al, 1989;Wackett et al, 1989) and MTBE (Deeb et al, 2001;Smith et al, 2003). In the case of trichloroethene, this oxidation reaction can be catalyzed by both monooxygenases (Leahy et al, 1996;Shields et al, 1989) and dioxygenases (Leahy et al, 1996;Nelson et al, 1988;Wackett and Gibson, 1988;Zylstra et al, 1989). The relaxed regiospecificity found in enzymes that are functionally analogous to those determined to degrade NDMA in higher organisms suggests that bacterial enzymes may have the capability to degrade NDMA.…”

Regiospecific oxidation of naphthalene and fluorene by toluene monooxygenases and engineered toluene 4‐monooxygenases of Pseudomonas mendocina KR1

“…In recent years, the toluene monooxygenases including toluene 4-monooxygenase (T4MO) of Pseudomonas mendocina KR1 (Whited and Gibson, 1991;Yen and Karl, 1992;Yen et al, 1991), TOM of B. cepacia G4 (Newman and Wackett, 1995;Shields et al, 1989), toluene/o-xylene monooxygenase (ToMO) of P. stutzeri OX1 (Bertoni et al, 1998;Cafaro et al, 2002), and toluene para-monooxygenase (TpMO) of Ralstonia pickettii PKO1 Olsen et al, 1994) have been studied extensively due to their potential in degrading environmental pollutants (Chauhan et al, 1998;Folsom and Chapman, 1991;McClay et al, 1996;Ryoo et al, 2000;Shim et al, 2001;Sun and Wood, 1996). They are soluble, nonheme, O 2 -dependent monooxygenases with multiple components, including a hydroxylase subunit that contains the catalytically active diiron cofactor (Leahy et al, 2003).…”

Degradation of toluene by a mixed population of archetypal aerobes, microaerophiles, and denitrifiers: Laboratory sand column experiment and multispecies biofilm model formulation

“…Organic pollutants are frequently found in aquifers where the dissolved oxygen concentration is usually low. Aromatic pollutants such as benzene, toluene, ethylbenzene, and xylene (BTEX) are degraded aerobically by means of oxygenasecatalyzed reactions, which require molecular oxygen for the hydroxylation of the aromatic ring, or an alkyl substitution (Assinder and Williams, 1990;Gibson et al, 1970;Robertson and Button, 1987;Shields et al, 1989). In the biodegradation of hydrocarbons, oxygen acts both as a co-substrate of the oxygenase enzyme and as a terminal electron acceptor for cellular respiration.…”