The Danube River is the second longest river in Europe, and its bacterial community composition has never been studied before over its entire length. In this study, bacterial community composition was determined by denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified portions of the bacterial 16S rRNA gene from a total of 98 stations on the Danube River (73 stations) and its major tributaries (25 stations), covering a distance of 2,581 km. Shifts in the bacterial community composition were related to changes in environmental conditions found by comparison with physicochemical parameters (e.g., temperature and concentration of nutrients) and the concentration of chlorophyll a (Chl a). In total, 43 distinct DGGE bands were detected. Sequencing of selected bands revealed that the phylotypes were associated with typical freshwater bacteria. Apparent bacterial richness in the Danube varied between 18 and 32 bands and correlated positively with the concentration of P-PO 4 (r ‫؍‬ 0.56) and negatively with Chl a (r ‫؍‬ ؊0.52). An artificial neural network-based model explained 90% of the variation of apparent bacterial richness using the concentrations of N-NO 2 and P-PO 4 and the distance to the Black Sea as input parameters. Between the cities of Budapest and Belgrade, apparent bacterial richness was significantly lower than that of other regions of the river, and Chl a showed a pronounced peak. Generally, the bacterial community composition developed gradually; however, an abrupt and clear shift was detected in the section of the phytoplankton bloom. Large impoundments did not have a discernible effect on the bacterial community of the water column. In conclusion, the riverine bacterial community was largely influenced by intrinsic factors.Prokaryotes play a major role in the biotic transformation of carbon and nutrients in aquatic ecosystems. Consequently, these organisms may alter the makeup of carbon and other chemicals during their transport in rivers. The sources, transport, and transformation of organic matter in rivers have been formalized conceptually (39, 40) and studied in situ (15). There is evidence that pelagic prokaryotic communities in rivers adapt to changes in the concentration and composition of organic carbon (20, 21) and nutrients (e.g., 3-5). Sekiguchi et al. (37) determined the bacterial community composition of the Changjiang River (China) as a reference for future changes caused by the construction of the Three Gorges dam. Their results showed that changes in the bacterial community (determined by denaturing gradient gel electrophoresis [DGGE] analysis and cloning) occurred gradually and that diversity decreased toward the river's delta near Shanghai.In this study, we focus on the bacterial community composition of the Danube River over its entire length in order to determine the effects of human influences (cities and impoundments) versus those of large tributaries and changes in the geomorphology in different sections of the river. The Danube River is the second longest ...

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A PCR-based denaturing-gradient gel electrophoresis (DGGE) approach was applied to a partial sequence of the ␤-D-glucuronidase gene (uidA) for specific detection and differentiation of Escherichia coli populations according to their uidA sequence variations. Detection of sequence variations by PCR-DGGE and by PCR with direct sequencing correlated perfectly. Screening of 50 E. coli freshwater isolates and reference strains revealed 11 sequence types, showing nine polymorphic sites and an average number of pairwise differences between alleles of the uidA gene fragments (screened fragment length, 126 bp) of 2.3%. Among the analyzed strains a range of dominating to more rarely and/or uniquely observed E. coli sequence types was revealed. PCR-DGGE applied to fecally polluted river water samples simultaneously detected E. coli and generated a fingerprint of the mixed populations by separating the polymorphic uidA amplicons. No significant differences between non-cultivation-based and cultivation-based profiles were observed, suggesting that at least some members of all occurring sequence types could be cultivated. As E. coli is frequently used as a fecal indicator, this work is considered an important step towards a new, practical tool for the differentiation and tracing of fecal pollution in all kinds of waters.Escherichia coli contamination is a widely used parameter for the examination of various kinds of waters. The detection of E. coli in temperate freshwaters usually provides a reliable indication of fecal pollution from humans and warm-blooded animals (14, 33). Recently, efficient cultivation media for routine monitoring of E. coli in environmental freshwaters have been developed (2,9,20). Those methods are generally applied in a quantitative way to estimate the actual concentration of E. coli. No information about the qualitative composition of different strains and clones can be gained (3,14). Differentiation is not the main purpose for most routine applications, although there is a considerable demand for techniques for the simultaneous detection and differentiation of E. coli populations in aquatic habitats. A practical method generating a representative genetic fingerprint of population structures would enable routinely performed qualitative investigations such as the comparison of different sources of fecal emissions (e.g., effluents from different sewage treatment plants or human versus nonhuman fecal pollution).Several methods are available for the identification, characterization, and typing of microorganisms (34). So far, serotyping, biotyping, multilocus enzyme electrophoresis (MLEE), profiling for insertion elements and plasmids, restriction fragment length polymorphism analysis, random amplified polymorphic DNA analysis, amplified restriction fragment polymorphism analysis, ribotyping, pulsed-field gel electrophoresis, DNA sequencing, and detection of a genome polymorphism marker by PCR have been used for typing of E. coli cells, representing low-to high-range resolution techniques (8, 13, 16, 17,...

The River Danube was studied in the vicinity of Vienna (Austria) to examine the Interactions among suspended matter, bacterial colonization and dissolved organic matter on a medium temporal and spatial scale. The concentration of suspended matter, the total number of particles and the number of bacteria attached to particles correlated with discharge rates. In the River Danube, 39% of the particles stained with Alcian Blue were colonized by bacteria, but only a small number of particles were heavily colonized. About 9.5% of the total bacterial community was found to b e associated with particles, abundance of free-living bacteria varied between 2.4 and 7.8 X 106 cells ml-' and attached bactenal abundance varied from 0.1 to 1.4 X 106 cells ml-l On average, 8 bacteria particle-' were found in the River Danube. Smaller particles were colonized more densely by bacteria than larger particles In the River Danube, 60 % of the particles were found to be in the size range of > 9 to 100 pm2 and 57 ' % of the attached bacteria colonized thls slze class.

Wild birds are an important nonpoint source of fecal contamination of surface waters, but their contribution to fecal pollution is mostly difficult to estimate. Thus, to evaluate the relation between feces production and input of fecal indicator bacteria (FIB) into aquatic environments by wild waterfowl, we introduced a new holistic approach for evaluating the performance of FIB in six shallow saline habitats. For this, we monitored bird abundance, fecal pellet production, and the abundance of FIB concomitantly with a set of environmental variables over a 9-month period. For estimating fecal pellet production, a new protocol of fecal pellet counting was introduced, which was called fecal taxation (FTX). We could show that, over the whole range of investigated habitats, bird abundance, FTX values, and FIB abundance were highly significantly correlated and could demonstrate the good applicability of the FTX as a meaningful surrogate parameter for recent bird abundances and fecal contamination by birds in shallow aquatic ecosystems. Presumptive enterococci (ENT) were an excellent surrogate parameter of recent fecal contamination in these saline environments for samples collected at biweekly to monthly sampling intervals while presumptive Escherichia coli and fecal coliforms (FC) were often undetectable. Significant negative correlations with salinity indicated that E. coli and FC survival was hampered by osmotic stress. Statistical analyses further revealed that fecal pollution-associated parameters represented one system component independent from other environmental variables and that, besides feces production, rainfall, total suspended solids (direct), and trophy (indirect) had significant positive effects on ENT concentrations. Our holistic approach of linking bird abundance, feces production, and FIB detection with environmental variables may serve as a powerful model for application to other aquatic ecosystems.Wild waterfowl are known to be an important nonpoint source of fecal contamination of surface waters (1,8,15,25,30). Wild birds have been reported to excrete large amounts of fecal indicator bacteria (FIB) (8, 25) and occasionally harbor enteric pathogens (20,21). Especially for public swimming beaches, fecal contamination by wild birds can therefore impose a severe problem for the persons in charge to meet the legal limits for FIB. Locating the source of contamination, however, is often a tricky business, and the contribution of wild birds to the total contamination of surface waters is mostly difficult to estimate. Thus, it would be considerably helpful to better understand the relations between feces production by wild waterfowl and their input of FIB into aquatic environments.We therefore monitored, over a 9-month period, the relations between bird abundances, their fecal pellet production, and three groups of FIB in six shallow, modestly saline aquatic environments. As the investigated saline pools are nearly exclusively visited by birds and no other animals and because they exhibit a steep gradien...