FEMS Microbiology Reviews 15 (1994) 279-295 ¢3 1994 Federation of European Microbiological Societies 0168-6445/94/$15.00 Published by Elsevier 279 FEMSRE 00436 Degradation of halogenated The role of adaptation aliphatic compounds: F. Pries, J.R. van der Ploeg, J. Dolfing and D.B. Janssen * Department of Biochemistry, Unit~ersity of Groningen, Nijenborgh 4, 9747 A G Groningen, the Netherlands Abstract: A limited number of halogenated aliphatic compounds can serve as a growth substrate for aerobic microorganisms. Such cultures have (specifically) developed a variety of enzyme systems to degrade these compounds. Dehalogenations are of critical importance. Various heavily chlorinated compounds are not easily biodegraded, although there are no obvious biochemical or thermodynamic reasons why microorganisms should not be able to grow with any halogenated compound. The very diversity of catabolic enzymes present in cultures that degrade halogenated aliphatics and the occurrence of molecular mechanisms for genetic adaptation serve as good starting points for the evolution of catabolic pathways for compounds that are currently still resistant to biodegradation. Key words': Adaptation; Evolution; Dehalogenase; Chloroacetate; 1,2-Dichloroethane; Trichloroethylene Introduction Chlorinated aliphatic compounds form one of the most important groups of industrially pro- duced chemicals. Several of these compounds are poorly degraded in the environment and in bio- logical treatment systems. This lack of biodegra- dation is mainly related to biochemical factors rather than to thermodynamics, Both oxidative conversion of chlorinated compounds with oxygen as the electron acceptor and reductive degrada- tion to methane or alkanes should yield sufficient energy to support growth [1]. The recalcitrance thus is caused by the absence of metabolic routes that produce energy and intermediates in a form that can be used for biosynthetic processes. * Corresponding author. The absence of these routes is related to the xenobiotic character of the molecules: the com- pounds are not properly recognized by uptake proteins, regulatory proteins, or catabolic en- zymes whose function is essential for metabolism. With chloroaliphatics, the lack of enzymes that can catalyze the required catabolic steps will be most important since the lack of induction could be overcome easily by constitutive expression. With the exception of halocarboxylic acids [2], there is no evidence for a role of uptake proteins. As a result of the absence of efficient catabolic enzymes, compounds may be completely inert, they may be partially degraded, toxicity may oc- cur, etc. Toxicity can be caused by the accumula- tion of intermediates that are chemically reactive towards biological macromolecules or that disturb normal metabolism. For example, the epoxides and acylchlorides produced by oxidative conver- SSDI 0168-6445(94)00038-Z Downloaded from https://academic.oup.com/femsre/article/15/2-3/279/615058 by guest on 08 July 2022