These ‘‘fitter’’ strains eventually form the bulk of the community and plating out under selective conditions is then used to isolate the strains of interest. Studies on these isolates have provided valuable information on their metabolism and physiology, but the conditions necessary to achieve successful enrichment are so far away from those found in the natural source of the initial inoculum that it is doubtful, in many cases, that the isolates could perform a significant role in the environment from which they were derived. For example, successful classical enrichment requires an environment of nutrient excess, whereas unpolluted environments are typically nutrient-limited.