Numerical taxonomic analysis of bacterial guild structure in aquatic environments

A total of 210 bacterial strains was isolated using the four media from a single sample site located on an oligotrophic reservoir. The strains were examined for 158 morphological, physiological and biochemical characters. The results were coded and examined using numerical taxonomy. Including unclustered strains, a total of 100 taxa were characterized which indicated extremely high apparent diversity. When compared one to another, all four media were found to be somewhat selective in regards to taxa recovered. Taxa characterized from strains isolated from YEPGA and PHA were almost mutually exclusive. The difference could not be attributed solely to strain concentration in the water at the time of sampling.

Further studies using PHA as the isolation medium were carried out using sediment samples from a shallow freshwater stream. A total of 60 strains was isolated and examined using phenetic and chemotaxonomic methods. For the phenetic portion of the investigation the strains were characterized using 84 morphological, physiological and biochemical characters. The results were coded and examined using numerical taxonomy. Using methylated fatty acids and gas chromatography, cellular fatty acid profiles were obtained from the strains. These data also were coded and examined using numerical taxonomy.

In both the phenetic and the chemotaxonomic classifications over 80 percent of the bacterial strains were recovered in groups. Totals of 12 and 11 groups were defined in the phenetic and chemotaxonomic classifications respectively. Both classification systems were good in that they were reproducible on a strain by strain basis, discriminating and not based on negative matching. Group to group correspondence of strains from one system to the other was not observed. To some extent inter- and intra- group similarities in both classification systems could be used to predict strain recovery from one system to the other.

It was suggested that the lack of congruence between the phenetic and chemotaxonomic classification systems could be due to the nature of the aquatic environment and the characteristics of bacteria adapted to that environment. The pattern of variation observed between the two systems could be explained by the presence of bacterial taxa with wide and varied physiological and biochemical capabilities, and short term adaptation of these bacterial taxa to the changing potential roles present in the aquatic community. The physiological and biochemical variance of taxa, and the occurence of relatively diverse taxa within a phenetic group may be significant contributing factors to identification problems often encountered in microbial ecology and environmental microbiology.