A high biomasses of Cladophora, a filamentous green alga, is found mainly during the summer along the shores of Lake Michigan. In this study, the abundance and persistence of the fecal indicator bacterium Escherichia coli and sulfate-reducing bacteria (SRB) on Cladophora mats collected at Lake Michigan beaches were evaluated using both culture-based and molecular analyses. Additionally, 16S rRNA gene cloning and sequencing were used to examine the bacterial community composition. Overall, E. coli was detected in all 63 samples obtained from 11 sites, and the average levels at most beaches ranged from 2,700 CFU/100 g (wet weight) of Cladophora to 7,500 CFU/100 g of Cladophora. However, three beaches were found to have site average E. coli densities of 12,800, 21,130, and 27,950 CFU/100 g of Cladophora. The E. coli levels in the lake water collected at the same time from these three sites were less than the recommended U.S. Environmental Protection Agency limit, 235 CFU/100 ml. E. coli also persisted on Cladophora mats in microcosms at room temperature for more than 7 days, and in some experiments it persisted for as long as 28 days. The SRB densities on Cladophora mats were relatively high, ranging from 4.4 ؋ 10 6 cells/g (6.64 log CFU/g) to 5.73 ؋ 10 6 cells/g (6.76 log CFU/g) and accounting for between 20% and 27% of the total bacterial counts. Partial sequences of the 16S rRNA gene clones revealed a phylogenetically diverse community, in which the CytophagaFlavobacterium-Bacteroides cluster and the low-G؉C-content gram-positive bacteria were the dominant organisms, accounting for 40% and 12.8%, respectively, of the total clone library. These results further reveal the potential public health and ecological significance of Cladophora mats that are commonly found along the shoreline of Lake Michigan, especially with regard to the potential to harbor microorganisms associated with fecal pollution and odor-causing bacteria.

Dissolved organic matter (DOM) and inorganic nutrients may affect microbial communities in streams, but little is known about the impact of these factors on specific taxa within bacterial assemblages in biofilms. In this study, nutrient diffusing artificial substrates were used to examine bacterial responses to DOM (i.e., glucose, leaf leachate, and algal exudates) and inorganic nutrients (nitrate and phosphate singly and in combination). Artificial substrates were deployed for five seasons, from summer 2002 to summer 2003, in a northeastern Ohio stream. Differences were observed in the responses of bacterial taxa examined to various DOM and inorganic nutrient treatments, and the response patterns varied seasonally, indicating that resources that limit the bacterial communities change over time. Overall, the greatest responses were to labile, low-molecular-weight DOM (i.e., glucose) at times when chlorophyll a concentrations were low due to scouring during significant storm events. Different types of DOM and inorganic nutrients induced various responses among bacterial taxa in the biofilms examined, and these responses would not have been apparent if they were examined at the community level or if seasonal changes were not taken into account.Biofilms play important roles in ecosystem processes in streams (35), and factors responsible for the abundance and distribution of microorganisms in such communities have often been studied (e.g., references 12, 16, 17, 33, 45, and 48). Inorganic nutrients (11, 18) and dissolved organic matter (DOM) (17,23,44,45) have been shown specifically to influence microbial abundance in aquatic biofilms (31,48,51).The source, quality, and type of DOM, as well as the quantity, may influence the abundance and distribution of bacteria in stream ecosystems (20,21,24). In addition, other aspects of microbial community function such as respiration, biomass, and extracellular enzyme activity may be limited by dissolved inorganic nutrients and organic matter in streams (49, 51). Also, epilithic bacterial populations can be affected indirectly by inorganic nutrients via the influence of nutrients on algal biomass (45,50).In spite of the number of studies that have looked at responses of microorganisms in streams to DOM and inorganic nutrients, little is known about the influence of nutrients and DOM on the composition and distribution of different bacterial taxa in stream biofilms. This is because earlier investigations were typically based on assemblage-level responses, such as examining total bacterial numbers (e.g., references 16, 24, 31, and 45), with few examining spatial and temporal changes in specific bacterial populations (4,20,32). In this study, we examined how different bacterial taxa in biofilms responded to DOM and inorganic nutrients by using nutrient diffusing artificial substrates (clay flowerpots), an approach commonly used to demonstrate nutrient limitation in streams (e.g., references 11 and 43). Responses to different treatments (leaf leachate [LL], glucose, algal exudate...

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 ...

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The study investigated the occurrence of antimicrobial resistance genes and virulence determinants in Vibrio species recovered from different freshwater sheds in rustic milieu. A total of 118 Vibrio isolates comprising Vibrio fluvialis (n=41), Vibrio mimicus (n=40) and V. vulnificus (n=37) was identified by amplification of ToxR, vmh and hsp60 genes. The amplification of virulence genes indicated that V. mimicus (toxR, zot, ctx, VPI, and ompU) genes were detected in 12.5%, 32.5%, 45%, 37.5% and 10% respectively. V. fluvialis genes (stn, hupO and vfh) were harboured in 48.8%, 14.6% and 19.5% isolates congruently. The other virulence genes that include vcgC and vcgE were observed in 63.1% and 29% of isolates belonging to V. vulnificus. With the exceptions of imipenem, meropenem and ciprofloxacin, most isolates exhibited more than 50% resistance to antibiotics. The antimicrobial resistance was more prevalent for polymyxin B (100%), azithromycin (100%) and least in ciprofloxacin (16.1%). Multiple antibiotic resistance index range was 0.3 and 0.8 with most isolates showing MARI of 0.8. The blaTEM, AmpC, blaGES, blaIMP, blaOXA-48 and blaKPC genes were detected in 53.3%, 42%, 29.6%, 16.6%, 15%, 11.3% and 5.6% of the isolates. Non-beta lactamases such as streptomycin resistance (aadA and strA), gentamicin resistance (aphA1) and quinolone resistance gene (qnrVC) were found in 5.2%, 44.3%, 26% and 2.8%. Chloramphenicol resistance genes (cmlA1 and catII) were found in 5.2% and 44.3% among the isolates. Our findings reveal the presence of antimicrobial resistance genes and virulent Vibrio species in aquatic environment which can have potential risk to human and animal’s health.