Alexander K. T. Kirschner

Seasonal successions and trophic relations between phytoplankton, zooplankton, ciliate and bacteria in a hypertrophic shallow lake in Vienna, Austria

Alte Donau nowadays is an eutrophic urban lake within the cityofVienna. Increasing nutrient concentrations and massive bloomsofcyanobacteria mainly caused by Limnothrix redekei VanGoorand Cylindrospermopsis raciborskii (Wolsz.) SeenayyaetSubba Raju were recently registered. As a consequence Secchidepthwas significantly reduced especially during the summer season(minimum: 0.25 m). An investigation including water chemistry,phytoplankton, macrophytes, and sediment was initiated in 1993andextended to metazooplankton, ciliates and bacteria in 1994.Thefirst half of the year 1994 was characterised by relativelyclearwater and a high diversity of the phytoplankton compositiondue toflushing of the lake with water of better quality by the endof1993. Ciliates and metazooplankton held about 10% of thetotalbiomass of all the investigated trophic levels. The vanishingofthe remaining macrophytes enlarged the nutrient supply duringsummer 1994 and favoured the development of cyanobacteria. Thehighwater temperatures which excluded certain zooplankton species,andthe inedibility of the filaments further increased thedominance ofcyanobacteria. In November, when the algal bloom finallyceased,the highest bacterial numbers of the investigation periodoccurred.Thereafter, other algal groups, bacteria and metazooplanktongainedmore importance.Interactions are possible because of close overlap in spaceandtime due to the turbulent mixed conditions of the water bodyandthe change from the macrophyte dominated to the algaldominatedstable state. Planned restoration measures must aim tore-establishthe previous macrophyte dominated clear-waterstage.

Microbiological water quality along the Danube River: Integrating data from two whole-river surveys and a transnational monitoring network

The River Danube is, with 2780 km, the second longest river in Europe. Its catchment area covers 801 500 km(2), with approximately 81 million inhabitants in 19 countries. River water for anthropogenic use, transportation and recreation is of major importance in all of these countries. Microbiological contamination from faecal pollution by anthropogenic sources is considered to be a crucial problem throughout the Danube River basin. Thus, detailed knowledge on the extent and the origin of microbial pollution is essential for watershed management. The determination of faecal indicator concentrations along the Danube and its major tributaries during two whole-river surveys and 16 permanent stations allowed for the first time to draw a clear picture of the faecal pollution patterns along the whole longitudinal profile of this important international river. By including a variety of environmental variables in statistical analysis, an integrative picture of faecal pollution in the Danube River basin could be evolved. Four hot spots and six stretches of differing faecal pollution were identified, mainly linked with input from large municipalities. Significant decline of microbiological pollution was observed in the upper and lower Danube stretches over the investigation period. In contrast, a significant increase in the middle part was evident. The planned implementation of new wastewater treatment plants and advanced wastewater treatment measures according to the European Union urban wastewater directive will have a great potential to reduce microbial faecal pollution in the Danube and thus improving water quality.

Bacterial diversity along a 2600 km river continuum

Summary The bacterioplankton diversity in large rivers has thus far been under‐sampled despite the importance of streams and rivers as components of continental landscapes. Here, we present a comprehensive dataset detailing the bacterioplankton diversity along the midstream of the Danube River and its tributaries. Using 16S rRNA‐gene amplicon sequencing, our analysis revealed that bacterial richness and evenness gradually declined downriver in both the free‐living and particle‐associated bacterial communities. These shifts were also supported by beta diversity analysis, where the effects of tributaries were negligible in regards to the overall variation. In addition, the river was largely dominated by bacteria that are commonly observed in freshwaters. Dominated by the acI lineage, the freshwater SAR11 (LD12) and the P olynucleobacter group, typical freshwater taxa increased in proportion downriver and were accompanied by a decrease in soil and groundwater‐affiliated bacteria. Based on views of the meta‐community and River Continuum Concept, we interpret the observed taxonomic patterns and accompanying changes in alpha and beta diversity with the intention of laying the foundation for a unified concept for river bacterioplankton diversity.

Escherichia coli and enterococci are sensitive and reliable indicators for human, livestock and wildlife faecal pollution in alpine mountainous water resources

Aims:  This study evaluated the applicability of standard faecal indicator bacteria (SFIB) for alpine mountainous water resources monitoring.

Rapid Growth of Planktonic Vibrio cholerae Non-O1/Non-O139 Strains in a Large Alkaline Lake in Austria: Dependence on Temperature and Dissolved Organic Carbon Quality

ABSTRACT Vibrio cholerae non-O1/non-O139 strains have caused several cases of ear, wound, and blood infections, including one lethal case of septicemia in Austria, during recent years. All of these cases had a history of local recreational activities in the large eastern Austrian lake Neusiedler See. Thus, a monitoring program was started to investigate the prevalence of V. cholerae strains in the lake over several years. Genetic analyses of isolated strains revealed the presence of a variety of pathogenic genes, but in no case did we detect the cholera toxin gene or the toxin-coregulated pilus gene, both of which are prerequisites for the pathogen to be able to cause cholera. In addition, experiments were performed to elucidate the preferred ecological niche of this pathogen. As size filtration experiments indicated and laboratory microcosms showed, endemic V. cholerae could rapidly grow in a free-living state in natural lake water at growth rates similar to those of the bulk natural bacterial population. Temperature and the quality of dissolved organic carbon had a highly significant influence on V. cholerae growth. Specific growth rates, growth yield, and enzyme activity decreased markedly with increasing concentrations of high-molecular-weight substances, indicating that the humic substances originating from the extensive reed belt in the lake can inhibit V. cholerae growth.

Rapid enzymatic detection of Escherichia coli contamination in polluted river water.

Aims: The relationship between the rate of β‐D‐glucuronidase hydrolysis (GLUase‐HR) and the E. coli concentration in rivers differing in the extent of faecal pollution was investigated. It was hypothesized that the rate of GLUase‐HR is a better surrogate parameter for E. coli concentrations than estimated numbers of faecal coliforms (FC).

A Seasonal Study of Bacterial Community Succession in a Temperate Backwater System, Indicated by Variation in Morphotype Numbers, Biomass, and Secondary Production

A bstractThe investigation of the bacterial community in the Kühwörter Wasser, a macrophyte-dominated arm of the River Danube backwater system near Vienna, revealed that variation in microbial densities and biomass could be related to a characteristic sequence in morphotype composition over the seasons. Maximal bacterial cell numbers and biomass occured in early summer, with values of up to 9 × 109 cells l−1 and 122 μg C l−1, respectively, caused by a massive increase of vibrio-shaped cells. On the other hand, in early spring, filamentous bacteria were responsible for a marked increase in bacterial biomass, making up 40% of the total bacterial biomass. Over the year, rod-shaped cells were the dominating morphotype, while the biomass of cocci was rather negligible. In winter, cell numbers and biomass showed minimal values with 2.0 × 109 cells l−1 and 28 μg C l−1, respectively, and bacteria were considered to be substrate and temperature limited during this period. Saturation values of the incorporation of 3H-thymidine into DNA, for the estimation of bacterial secondary production, varied seasonally, ranging from 5 nm to 40 nm. Thus, saturation experiments needed to be conducted on a regular basis. Also, the amount of labeled thymidine in the DNA, as a percentage of labeled thymidine in the TCA precipitate, varied over the year. Minimum values of 45% were recorded during the cold season, while maximum values of 75–80% at the beginning of June coincided with high chlorophyll a values and minimal Km-values derived from saturation experiments. The potential role of the nitrogen-rich nucleoside thymidine as a readily utilizable substrate for bacteria during labeling experiments, under varying conditions of substrate availability, is discussed. Bacterial secondary production rates ranged from 0.3 μg C l−1 h−1 in winter to values of 10 μg C l−1 h−1 in August, where phytoplanktonic biomass reached the summer maximum, and bacterial biomass was calculated to be renewed 3 times per day. An estimation of the bacterial carbon demand showed that for the major part of the year, with the exception of early spring, the bacterioplankton community in the Kühwörter Wasser was dependent on carbon sources other than phytoplanktonic primary production.

Does Virus-Induced Lysis Contribute Significantly to Bacterial Mortality in the Oxygenated Sediment Layer of Shallow Oxbow Lakes?

ABSTRACT Despite the recognition that viruses are ubiquitous components of aquatic ecosystems, the number of studies on viral abundance and the ecological role of viruses in sediments is scarce. In this investigation, the interactions between viruses and bacteria were studied in the oxygenated silty sediment layer of a mesotrophic oxbow lake. A long-term study (13 months) and a diel study revealed that viruses are a numerically important and dynamic component of the microbial community. The abundance and decay rates ranged from 4.3 × 109 to 7.2 × 109 particles ml of wet sediment−1 and from undetectable to 22.2 × 107 particles ml−1 h−1, respectively, and on average the values were 2 orders of magnitude higher than the values for the overlying water. In contrast to our expectations, viruses did not contribute significantly to the bacterial mortality in the sediment, since on average only 6% (range, 0 to 25%) of the bacterial secondary production was controlled by viruses. The low impact of viruses on the bacterial community may be associated with the quantitatively low viral burden that benthic bacteria have to cope with compared to the viral burden with which bacterial assemblages in the water column are confronted. The virus-to-bacterium ratio of the sediment varied between 0.9 and 3.2, compared to a range of 5.0 to 12.4 obtained for the water column. We speculate that despite high numbers of potential hosts, the possibility of encountering a host cell is limited by the physical conditions in the sediment, which is therefore not a favorable environment for viral proliferation. Our data suggest that viruses do not play an important role in the processing and transfer of bacterial carbon in the oxygenated sediment layer of the environment investigated.

The emergence of Vibrio pathogens in Europe: ecology, evolution, and pathogenesis (Paris, 11-12th March 2015).

Global change has caused a worldwide increase in reports of Vibrio-associated diseases with ecosystem-wide impacts on humans and marine animals. In Europe, higher prevalence of human infections followed regional climatic trends with outbreaks occurring during episodes of unusually warm weather. Similar patterns were also observed in Vibrio-associated diseases affecting marine organisms such as fish, bivalves and corals. Basic knowledge is still lacking on the ecology and evolutionary biology of these bacteria as well as on their virulence mechanisms. Current limitations in experimental systems to study infection and the lack of diagnostic tools still prevent a better understanding of Vibrio emergence. A major challenge is to foster cooperation between fundamental and applied research in order to investigate the consequences of pathogen emergence in natural Vibrio populations and answer federative questions that meet societal needs. Here we report the proceedings of the first European workshop dedicated to these specific goals of the Vibrio research community by connecting current knowledge to societal issues related to ocean health and food security.

Heterotrophic prokaryotic production in ultraoligotrophic alpine karst aquifers and ecological implications.

Spring waters from alpine karst aquifers are important drinking water resources. To investigate in situ heterotrophic prokaryotic production and its controlling factors, two different alpine karst springs were studied over two annual cycles. Heterotrophic production in spring water, as determined by [(3)H]leucine incorporation, was extremely low ranging from 0.06 to 6.83 pmol C L(-1) h(-1) (DKAS1, dolomitic-karst-spring) and from 0.50 to 75.6 pmol C L(-1) h(-1) (LKAS2, limestone-karst-spring). Microautoradiography combined with catalyzed reporter deposition-FISH showed that only about 7% of the picoplankton community took up [(3)H]leucine, resulting in generation times of 3-684 days. Principal component analysis, applying hydrological, chemical and biological parameters demonstrated that planktonic heterotrophic production in LKAS2 was governed by the respective hydrological conditions, whereas variations in DKAS1 changed seemingly independent from discharge. Measurements in sediments recovered from LKAS2, DKAS1 and similar alpine karst aquifers (n=12) revealed a 10(6)-fold higher heterotrophic production (average 19 micromol C dm(-3) h(-1)) with significantly lower generation times as compared with the planktonic fraction, highlighting the potential of surface-associated communities to add to self-purification processes. Estimates of the microbially mediated CO(2) in this compartment indicated a possible contribution to karstification.