ENVIRONMENTAL BIOTECHNOLOGY FOR LAUNCHING THE 21st CENTURY.

James M. Tiedje, Center for Microbial Ecology, Michigan State University, East Lansing, Michigan 48824, USA

The simplest forms of bioremediation have now become accepted bioremediation technologies; these include bioventing of gasoline, landfarming of petroleum contaminated soils and other readily degradable chemicals, and co-composting of some pesticides. These more easily practiced technologies are basically aerobic processes, employ indigenous microbes that can grow on the pollutant and are widely distributed in nature in high numbers. The less readily degradable pollutants remain a challenge. New technologies are needed. These include organisms with new biochemical properties, mechanisms to cost-effectively disperse microorganism in soil and sediment, biodegradative organisms that use available electron acceptors other than oxygen, non-toxic technologies that enhance bioavailability, and methodologies to assess and track active microorganisms in the field.

For evaluating the potential for bioremediation at a site, I advise the practitioner to ask the following three simple questions. 1) What is the evidence (in the literature) that the chemical is biodegradable, and is it degraded by co-metabolism or is it a growth substrate? By now a good record exists on the biodegradability of most chemicals that might reach the environment. Also, biodegradation is much easier to implement if the chemical is a growth substrate, either as a carbon and energy source or as an energy-coupled electron acceptor. 2) Is the site habitable to life? If it is too toxic, there is no chance for biological processes to exist. 3) What is limiting the rate of biodegradation and can it be modified? Often this question is not answered and technologies implemented without knowing if it addresses the rate-limiting parameter.

I will use results from four research projects to illustrate some key points as well as show new technologies under investigation at our Center. One of the currently popular technologies in the US is intrinsic remediation, a process in which one relies on the native populations and conditions, but requires documentation of the process, the rates and that it can be sustained to eventually remove the pollutant. One general question related to use of indigenous organisms is how widely distributed are organisms of the same or very similar genotype, in other words are biodegrading organisms endemic or cosmopolitan? Results of our global studies on this question will be compared for chlorobenzoate degrading organisms, for Pseudomonas fluorescens, and for certain plasmids. Our Center is also conducting two field studies on new bioremediation approaches, one using biostimulation and bioaugmentation to achieve halorespiration of PCE to ethene at an aquifer near Lake Huron, and the other involves using bioaugmentation and niche adjustment to hydrolyze carbon tetrachloride in an aquifer in southwest Michigan. In both cases molecular tracking was used to help assess the effectiveness of the process. Finally, I will discuss our success in genetically constructing organisms that will grow on the PCBs that are the primary products of the reductive dechlorination of Aroclors, and strategies to use these organisms at a field site. Moving bioremediation technologies to a field evaluation stage requires a team effort since diverse expertise and much effort is needed. The work I will discuss involved more than 50 people, and their contributions are gratefully acknowledged.