In this study, the abundance of major bacterial taxa (based on fluorescent in situ hybridization, FISH) and the structure of the bacterial community (based on denaturing gradient gel electrophoresis, DGGE) were determined in the benthos of 9 streams in the southeastern and midwestern United States and related to differences in environmental conditions. Taxa examined via FISH were Domain Bacteria, Domain Archaea, α-, β-, and γ-Proteobacteria, a portion of the Bacteroidetes (formerly Cytophaga-Flavobacterium-Bacteroides), and Gram-positive bacteria with high (actinobacteria) and low percent guanine + cytosine (GC) content. Of these taxa, generally the most abundant were the β-and α-Proteobacteria, which constituted on average 19.5 and 17.0% of the Domain Bacteria, respectively. Abundance of most taxa was significantly different among streams and sites within a stream. Based on canonical correspondence and correlation analyses, β-and γ-Proteobacteria tended to be most abundant at sites with high dissolved organic carbon (DOC) and nitrate/nitrite concentrations and high benthic organic matter content. In contrast, α-Proteobacteria were more abundant in environments with low DOC and nitrate/nitrite concentrations and low sediment organic carbon content. The other taxa did not exhibit clear correlations with the environmental variables measured. DGGE results revealed that the structure of the bacterial community differed among the streams examined, with limited differences in a given stream and much larger differences among streams. Overall, there were clear differences in community composition that in some cases correlated with differences in environmental conditions. KEY WORDS: Bacteria · Fluorescent in situ hybridization · Denaturing gradient gel electrophoresis · Proteobacteria · Streams · Benthos Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 40: [51][52][53][54][55][56][57][58][59][60] 2005 regions (the southeastern and midwestern US) and observations were related to differences in environmental conditions in the streams. The abundance of major taxonomic groups, Domain Bacteria, Domain Archaea, α-, β-, and γ-Proteobacteria, a portion of the Bacteroidetes (formerly Cytophaga-Flavobacterium-Bacteroides), and Gram-positive bacteria with high (HGC) and low (LGC) percent guanine + cytosine (GC) content, was determined. These taxa were selected because of their documented occurrence in other streams (e.g. 2imek et al. 2001(e.g. 2imek et al. , Araya et al. 2003. In addition, bacterial community structure was examined using denaturing gradient gel electrophoresis (DGGE) (Muyzer et al. 1993), and within-stream variability was assessed.From prior studies on freshwater bacterial communities several trends emerge related to the occurrence of the taxa examined in this study. Specifically, Proteobacteria (particularly α, β, and γ subclasses), CytophagaFlavobacteria (Bacteroidetes), and Actinobacteria (HGC Gram-positive bacteria) are prevalent in lakes and streams ...

The population sizes of three bacterial species, Acinetobacter calcoaceticus, Burkholderia cepacia, and Pseudomonas putida, were examined in water and sediment from nine streams in different parts of the United States using fluorescent in situ hybridization (FISH). Population sizes were determined from three sites (upstream, midstream, and downstream) in each stream to compare differences in the occurrence and distribution of the species within each stream and among streams. Physical and chemical variables measured reflected differences in environmental conditions among the streams. In the water, B. cepacia numbers were highest in the agricultural, Iowa stream. P. putida numbers were highest in the southern coastal plain streams, Black Creek (GA) and Meyers Branch (SC). Compared to the other two species, the abundance of A. calcoaceticus was similar in all the streams. In sediment, the greatest abundance of all three species was found in the Iowa stream, while the lowest was in Hugh White Creek (NC). Detrended correspondence analysis (DCA) explained 95.8% and 83.9% of the total variation in bacterial numbers in water and sediment of the streams, respectively. In sediments and water, B. cepacia numbers were related to nitrate concentrations. A. calcoaceticus in water clustered with several environmental variables (i.e., SRP, pH, and conductivity) but benthic populations were less well correlated with these variables. This study reveals the potential influence of various environmental conditions on different bacterial populations in stream communities.

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Algal-bacterial co-variation has been frequently observed in lentic and marine environments, but the existence of such relationships in lotic ecosystems is not well established. To examine possible co-variation, bacterial number and chlorophyll-a concentration in water and sediments of nine streams from different regions in the USA were examined. In the water, a strong relationship was found between chlorophyll concentration and bacterial abundance. There was not a significant linear relationship between the abundance of sediment bacteria and sediment or water chlorophyll concentration. The linear regression results obtained between bacterial numbers and chlorophyll concentration in water were generally similar to those reported in other studies on lentic and marine systems suggesting that factors that cause this co-variation may be similar.

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