Characterization of Freshwater Diatom Communities: Comparing Taxonomic and Genetic-Fingerprinting Approaches.

Benthic diatom assemblages from five sampling sites located on two rivers were characterized simultaneously by means of traditional microscopic observations and PCR-DGGE fingerprinting with primers specifically designed for Bacillariophyceae. Community structure, richness, and diversity assessed by both methods were compared. Diatom lists obtained from morphological identification were separated into subsets, depending on (i) the taxonomic level considered (genus, species, variety) and, for each of them, (ii) the relative abundance (RA) of each component (the whole data set, RA > 1%, RA > 2%). These data were then compared to genetic fingerprinting data. Clusters based on taxonomic composition and DGGE banding patterns were very similar, showing good correspondence of community structure between the two methods. Data were compared by linear regressions between indices (richness, diversity) and by Mantel tests on dissimilarity matrices generated for each community composition data set. Statistical analysis indicated that the most reliable correlations with fingerprinting were obtained for genera representing more than 1% RA or species representing more than 2% RA. The results reveal that the PCR-DGGE protocol described here offers a satisfactory alternative for performing preliminary screening of coarse differences in diatom global community structure between samples. It can be regarded as a good complement to taxonomic analyses, which still remain necessary to detect precise changes in richness and diversity, especially when considering species with low abundance in natural assemblages.