Biofilm community structure in polluted rivers: abundance of dominant phylogenetic groups over a complete annual cycle

Abstract

The seasonal dynamics of river biofilm communities in two German rivers, the Elbe and one of its tributaries, the Spittelwasser, were investigated for the first time by using fluorescence in situ hybridization and a standardized biofilm sampling procedure. We show the importance of members of the beta subclass of the class Proteobacteria, which formed the largest single group in the massively polluted Spittelwasser at all times. Clear seasonal peaks of abundance were observed for the planctomycetes and the Cytophaga-Flavobacterium cluster.

FIG. 1

Seasonal fluctuations in the water temperatures in the Elbe and Spittelwasser rivers and in the chlorophyll a concentrations in the Elbe River.

FIG. 2

Sampling device for growing biofilms on glass plates in a river (biofilm collector). (A) Cross-sectional view (line II—II in panel B). (B) Top view (line I—I in panel A). 1 and 2, top and bottom plates with eight grooves for exposed glass plates (380 by 240 by 15 mm); 3, side plate (200 by 400 by 10 mm); 4, threaded metal rod (length, 750 mm); 5, exposed glass plate (200 by 400 by 4 mm); 6, groove for exposed glass plate (4.5 by 5 by 220 mm); 7, stabilizing bar (5 by 10 by 270 mm).

FIG. 3

Abundance of major phylogenetic groups in river biofilms during one annual cycle as determined by whole-cell hybridization of biofilm samples with rRNA-targeted fluorescent probes. Alpha, α-Proteobacteria; Beta, β-Proteobacteria; Gamma, γ-Proteobacteria; CF, CF cluster; GPHGC, gram-positive bacteria with high G+C contents. (A) Elbe River. (B) Spittelwasser River.

FIG. 4

Seasonal variation in abundance of members of the planctomycetes and the CF cluster (CF) in biofilms obtained from the Elbe River in 1994 (A) and 1997–1998 (B) and in biofilms obtained from the Spittelwasser River in 1997–1998 (C).