Bacterial taxonomy, which began as a largely intuitive process, has become increasingly objective with the advent of numerical taxonomy and techniques for the measurement of evolutionary divergence in the structure of semantides, i.e., large, information-bearing molecules such as nucleic acids and proteins. These developments have forced the

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Taxonomic and genetic diversities of microbial communities disturbed by chemical pollutants were lower than in undisturbed reference communities. The dominant populations within the disturbed communities had enhanced physiological tolerances and substrate utilization capabilities, indicating that generalized physiological versatility is an adaptive characteristic of populations that successfully compete within disturbed communities.

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During previous cooperative numerical taxonomic studies of slowly growing mycobacteria, the International Working Group on Mycobacterial Taxonomy described a number of strains whose taxonomic status was ambiguous. A new study of DNA, RNA, and proteins from 66 of these organisms was performed to correlate their properties with phenotypic clustering behavior; the results of this study permitted 5 1 of the strains studied to be assigned to known species. The methods used to characterize the semantides included nucleotide sequencing and assessment of levels of semantide relatedness by affinity binding techniques, including whole DNA-DNA hybridization, probe hybridization, and antibody binding. There was good overall agreement between the phenotypic and chemotaxonomic clusters and the groups of organisms identified by semantide analyses. Our results supported the conclusion that we should continue to rely on polyphasic taxonomy to provide satisfactory systematic resolution of members of the genus Mycobacterium. We identified no single 16s rRNA interstrain nucleotide sequence difference value that unequivocally defined species boundaries. DNA-DNA hybridization remains the gold standard, but common resources are needed to permit DNA-DNA hybridization analyses to be made available to laboratories that are not prepared to use this technology. One of the large novel clusters which we studied corresponds to the recently described species Mycobacterium interjecturn, a pathogen that resembles the ilonpathogen Mycobacterium gurdonae phenotypically, We also identified strains that appear to represent ribovars of Mycobacterium intracellulare which do not react with the commercial diagnostic probes that are currently used for identification of this species. Other branches or clusters consisted of too few strains to permit a decision about their taxonomic status to be made.Approximately 17 years ago the International Working Group on Mycobacterial Taxonomy (IWGMT) began a cooperative open-ended study in which phenotypically unusual strains of s l o~l y growing mycobacteria were collected on a continuing basis. These strains were distributed to participants in the open-ended study for characterization by a broad range of predominantly phenotypic tests, and at intervals the data obtained were subjected to numerical taxonomic (NT) analyses (29-32). The purpose of studying an expanding set of cultures was to characterize slowly growing mycobacterial strains that either represented uncommonly encountered species that had not been represented in previous cooperative studies (10, 25, 28) or belonged to clusters of previously unrecognized taxa. These analyses yielded expanded phenotypic characterizations of members of some clusters that had not been thoroughly characterized before, such as the clusters that included the type strains of Mycobacterium simiae, Mycobacterium szulgai, Mycobacterium asiaticum, and Mycobacterium malmoense (3 1). However, some individual strains and phenotypic clusters emerged that exhibited no unequivocal aff...