Polyphasic characterization of a suite of bacterial isolates capable of degrading 2,4-D

To develop a better understanding of the ecological aspects of microbial biodegradation, it is important to assess the phenotypic and biochemical diversity of xenobiotic degrading organisms. Forty-six bacterial isolates capable of degrading 2,4-dichlorophenoxyacetic acid (2,4-D) and representing several geographically distinct locations were characterized and placed into taxonomic groups based on the results of several independent analyses. The isolates were characterized based on Gram's reaction, colony morphology, cell morphology, fatty acid methyl ester (FAME) fingerprints, carbon substrate oxidation patterns (BIOLOG), DNA homology to whole-plasmid probes and repetitive extragenic palindromic (REP) fingerprints. Attempts to group organisms taxonomically based on colony morphology and cell morphology were largely unsuccessful. Both FAME and BIOLOG analyses were generally unable to provide reliable genus or species identifications of these environmental isolates by comparison of fingerprints or substrate use patterns to existing data bases. Modification of the standard protocols for these analyses, however, allowed taxonomic grouping of the isolates and the construction of new data bases, comprised solely of 2,4-D-degrading organisms, against which future novel isolates can be compared. Independent cluster analysis of the FAME and BIOLOG data shows that the isolates can be segregated into five taxonomic classes. The collection of 2,4-D-degrading isolates was also separated into five classes based on DNA homology to whole-plasmid probes obtained from individual isolates. REP analysis allowed isolates that likely represent the same (or very similar) organism(s) to be identified and grouped. Each of the analyses used represents a mechanistically different means of classifying organisms, yet the taxonomic groupings obtained by several of the methods (FAME, BIOLOG, DNA homology, and to some degree, REP analysis) were in good agreement. This indicates that the features discriminated by these different methods represent fundamental characteristics that determine phylogenetic groups of bacteria.