The widespread global distribution of chlorinated hydrocarbons, their high lipophilicity and their recalcitrance have contributed to their importance as environmental toxicants. Their metabolism under oxic and anoxic conditions mediated by prokaryotic and eukaryotic cells is discussed. Various aerobic bacteria are able to use chlorinated hydrocarbons as the sole source of carbon and energy and some anaerobic bacteria can use some of these as an artificial electron acceptor in reductive dechlorination. Liver enzymes are responsible for the formation of hydrophilic metabolites ready for excretion which often lead to highly reactive and potentially toxic intermediates. Whereas fungi, especially ligninolytic ones, usually only exhibit ‘side activities’ for chlorinated hydrocarbons. The capabilities of bacteria had led to the development of various bioremediation processes. Both, successes and failures within these processes are known. Therefore, current research aims at a better understanding of global community interactions.
Key Concepts:
Chlorinated hydrocarbons have been produced by the chemical industry since nearly a decade in large amounts, but they can also be observed as natural compounds, sometimes exceeding the industrially produced amounts.
Even though toxicological properties have pushed the chlorochemistry into the focus of considerable debate and governmental regulatory action, chlorinated hydrocarbons remain essential for certain applications.
The aerobic metabolism of chlorinated hydrocarbons by bacteria has been studied in detail and an immense amount of information is available on pathways, enzymes and genes involved in the mineralisation of chloroaromatics.
The anaerobic degradation of chlorinated hydrocarbons is due to the capablity of anaerobic bacteria to use them in anaerobic respiration, which results in dechlorination.
Dehalococcoides
organisms are the most versatile reductive dehalogenators as being capable to dehalogenate chlorinated dioxins, biphenyls, benzenes and vinyl chloride, among others.
Microbial activities have been widespread used for bioremediation purposes through natural attenuation, biostimulation and bioaugmentation.
The poor understanding of the functioning of the complex microbial activities
in situ
made bioremediation efforts quite unreliable.
The rapid development of molecular techniques in recent years allows immense insights into the processes
in situ
, but also on the overall physiology of biocatalysts.