Professor Christof Holliger
Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland.
Chlorinated solvents such as per- and trichloroethene (PCE/TCE) are among the most frequently encountered groundwater pollutants due to their widespread use in industry and dry cleaning of cloths. Bacteria able to use these pollutants as terminal electron acceptor in an anaerobic respiration process, so-called organohalide-respiring bacteria (OHRB), are present in many natural environments. They can convert PCE and TCE to ethene by reductive dechlorination, however, the intermediate vinyl chloride often accumulates in aquifers where spontaneous dechlorination occurs, a compound which is much more toxic than the parent compounds PCE and TCE. The genomes of several OHRB have been sequenced and show that they can contain multiple genes encoding putative reductive dehalogenases. The genomes also contain numerous genes encoding putative regulatory enzymes involved in expression of reductive dehalogenases. We try to unravel the substrate spectrum of these enzymes with an innovative biochemical approach creating hybrid proteins containing unknown and known parts of these regulatory enzymes. In addition, we also investigated how present knowledge on OHRB and reductive dehalogenases can be used to explain intermediate accumulation phenomena observed in different aquifers, and how one could even envisage reductive dechlorination as bioremediation process in source zones where acidification by fermentation and dechlorination is a major drawback for organohalide respiration to decontaminate such zones.
Christof Holliger is at present full professor of environmental biotechnology at the Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland. After obtaining a PhD from University of Wageningen, The Netherlands, in 1992, he worked as a group leader at the Swiss Federal Institute of Aquatic Science and Technology (Eawag, 1992-1998) before joining EPFL as assistant professor. Being originally trained as biologist, his research is mainly directed towards the microbial aspects of environmental biotechnology, however, not forgetting the applicability of the microbial processes and systems involved. Two main topics characterize the research activity, reductive dechlorination of chlorinated solvents such as per- and trichloroethene by anaerobic bacteria and wastewater treatment by aerobic granular sludge. In the former topic, the biochemical and physiological characteristics of the bacteria involved as well as their ecology are investigated. In the latter topic, research concentrates on the influence of wastewater composition on the most interesting ecosystem with its many different niches due to the redox gradients created in the granular biofilm.