“…Most early microbiological studies sought to determine the ability of a pure microbial culture to degrade a single substrate. Although pure culture studies have been useful in the investigation of basic microbial functions, recent laboratory-scale systems have emphasized the use of mixedcultures of microorganisms in aquifer material under more realistic environmental conditions (Ehrlich et al, 1982;Herbes and Schwall, 1978;Kuhn et al, 1985;Lee et al, 1984;Parsons et al, 1984;Parsons and Lage, 1985;Pritchard and Bourquin, 1984;Spain et al, 1980;Wilson and Wilson, 1985). Still, there are problems associated with the use of mixed-culture systems.…”