AME 33:217-224 (2003)  -  doi:10.3354/ame033217

ABSTRACT: PCR-DGGE analysis of a 16S rDNA fragment was used to determine spatial patterns of epilithic bacteria diversity over a 100 km river section. Epilithic biofilms were collected on natural substrata in a river reach (mid-slope of the river Garonne) where changes in epilithic bacterial activities and densities were expected due to the presence of a major urban centre (Toulouse city). Nitrogen and phosphorus forms increased 2- to 10-fold downstream of this urban centre. Close values of biomass (18 to 27 g m^-2 in 2000 and 10 to 16 g m^-2 in 2001), bacterial densities (3 to 11 × 10¹² cells m^-2 for total bacteria) and activities (3.6 mg N m^-2 h^-1 for nitrification and 0.3 to 1.1 mg N m^-2 h^-1 for denitrification) were recorded at the different sampling sites. Conversely, in regard to community composition, up- and downstream samples were discriminated between according to their banding patterns: >60% similarity within clusters versus <45% similarity between clusters as calculated with the Jaccard similarity index. Up- and downstream samples shared 50 of the 74 detected bands, the maximum number of bands being 45 for 1 sample. Derived from relative intensities, Simpson (ca. 0.034) and Shannon (ca. 5.06) diversity indices indicated diversified communities. For all of the tested samples, specific richness and diversity indices exhibited relatively homogeneous values, suggesting that there may be a similar level of diversity in biofilms from contrasting sources.

KEY WORDS: Biofilms · Bacterial diversity · DGGE fingerprinting · River Garonne