January 2008
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15 Reads
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8 Citations
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January 2008
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15 Reads
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8 Citations
October 2005
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47 Reads
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26 Citations
Aquatic Microbial Ecology
The present study focused on the optimization of procedures for the extraction of viruses from silty freshwater sediments for subsequent enumeration. Viral abundance in 2 different shallow backwater systems of the River Danube (Austria) ranged from 1.45 x 10(9) to 9.58 x 10(9) particles ml(-1) wet sediment. The highest virus yields from the bulk of the sediments were obtained by 1 min sonication (3 x 20 s intervals, with 10 s interruptions). An increase in sonication time of up to 5 min decreased viral counts by an average of 15 %. Since dissolved DNA within sediment samples could bind to the nucleic acid stain and thereby inflate viral estimates, sediment samples are often treated with DNase before the staining procedure. Moreover, they are usually centrifuged and diluted to a high extent in order to avoid interference of particulate material with virus counting. Centrifugation led to a reduction of viral numbers by 2 to 36 % compared to untreated samples and did not reduce the background fluorescence; thus counting of viruses was not facilitated. Diluting 2000 x with Milli-Q water always provided an average of 19 % lower viral numbers than diluting 4000 x. Treatment with DNase had no significant effect on virus counting, with viral numbers in untreated samples being on average 96 % of those in DNase-containing samples. Additionally, 2 different nucleic acid stains were compared-viruses stained with SYBR Gold fluoresced brighter than those stained with SYBR Green I and fluorescence lasted longer, while background fluorescence was reduced sufficiently, thus facilitating virus counting. Viral numbers using SYBR Gold were on average twice of those obtained with SYBR Green I. The mean efficiency of virus extraction was 88.8% using the protocol outlined in this paper, and was thus slightly higher than that obtained in previous sediment investigations.
January 2005
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7 Reads
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11 Citations
ALTEX: Alternativen zu Tierexperimenten
Botulinum neurotoxin C1 (BoNt C1) and its corresponding gene were detected in seven aquatic habitats covering a range of low (LR) to high risk (HR) avian. botulism outbreak areas during a study period of 10 months. Toxin and gene in sediment and avian faecal samples were analysed before (in situ) and after cultivation (in. vitro) by a newly adapted ELISA, the common mouse bioassay and by a recently described nested PCR protocol. BoNt C1 gene fragments were detected in 74% and 83% of all investigated sediment samples by in situ PCR and in vitro PCR, respectively, at comparable frequencies in HR and LR areas. Similar high values were also observed for faecal samples. No BoNt C1 could be detected in the sediment in situ, while 53% and 56% of all cultivated samples contained BoNt C1 as detected in the mouse bioassay and the ELISA, respectively. The percentage of BoNt C1 positive cultivated samples was significantly higher (2 fold) in HR areas than in LR areas. Hence, our data clearly indicate an increased ratio of potentially BoNt C1 producing clostridia to BoNt C1 genes as the frequency or likelihood of botulinum epizootics increases in the environment. In addition, the good correlation between the results from the ELISA and the mouse bioassay for all sediment and faecal samples (r=0.90, p < 0.001, n=121) indicates a high potential for the ELISA to reduce/replace the mouse bioassay for the detection of BoNt C1 in environmental samples.
June 1999
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39 Reads
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15 Citations
Aquatic Microbial Ecology
A seasonal study on the quantification of energy fluxes through the microbial compartment and on bacterial morphotype succession was performed in a hypertrophic shallow backwater branch, which had shifted from a macrophyte-dominated clear-water to a phytoplankton-dominated turbid-water state from 1992 to 1994. Filamentous cyanobacterial species dominated the phytoplanktonic compartment during summer. Bacterial numbers ranged from 2.7 x 109 to 9.8 x 109 cells l-1, corresponding to biomass values of 35 and 119 μg C l-1, respectively. Temperature, dissolved organic carbon (DOC), primary production and soluble phosphorus were found to explain most of the variation of bacterial numbers and biomass in the system. Bacterial morphotypes exhibited a seasonal succession pattern with rods and vibrios as the most abundant morphotypes. Vibrios dominated during the bloom of cyanobacterial in summer, while rods were found to increase rapidly after the breakdown of the bloom in autumn and winter. Filamentous bacteria with cell lengths of up to 120 μm bloomed during a short period in spring, making up more than 60% of the total bacterial biomass. With principal component analysis we could extract 2 main factors influencing the variation of bacterial morphotypes, namely an abiotic/inorganic factor, containing temperature, oxygen, nitrate and ammonium, and a trophic factor, containing DOC, total nitrogen, total phosphorus and chlorophyll a. Variation of filamentous bacteria, however, could not be explained by these 2 factors. Bacterial secondary production amounted on average to 3.1 μg C l-1 h-1 with a range from 0.5 to 7.0 μg C l-1 h-1. The impact of top-down factors like grazing and viral lysis is expected to influence both the occurrence of filamentous bacteria and bacterial production rates. Enzyme kinetics of β-glucosidase, leu-aminopeptidase and alkaline phosphatase were established and the relations to the other investigated parameters are described. By integrating the phosphatase and aminopeptidase activity into a phosphorus and nitrogen budget for the bacterial and phytoplanktonic compartment in the Alte Donau, we were able to show that there was no P limitation over the whole year, while N was possibly limiting at the beginning of algal blooms. On an annual basis primary production exceeded by far the bacterial carbon demand, but periods with the reverse situation occurred from October to May. Temperature and carbon supply were seen as the main factors for limiting bacterial growth in the Alte Donau during the cold months. The importance of viral lysis and predation in controlling bacterial growth during the summer months was pointed out. A comparison of the investigated bacterial parameters with those of a mesotrophic but macrophyte-dominated branch of the same backwater system led us to the conclusion that the equilibrium shift of the Alte Donau has resulted in high primary production of the autotrophic procaryotic compartment but not in the expected increase of energy flux through the compartment of the heterotrophic bacterioplankton.
May 1999
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22 Reads
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31 Citations
Aquatic Microbial Ecology
The validity of the H-3-leucine centrifugation method for determining bacterial secondary production in oligotrophic and eutrophic fresh- and seawater samples was examined. For freshwater samples, we found that the established protocol developed by Smith & Azam (1992) led to significantly lower values (up to 57%) than a novel protocol presented here, where bacterial proteins are precipitated under acidic conditions (trichloroacetic acid) at 4 degrees C with a humic extract and solubilizing DNA and RNA at 100 degrees C for 30 min. For seawater samples, no difference was found when an ethanolic washing step was included in the novel protocol. We also used different salt solutions instead of humic extract; these both act as co-precipitants for the precipitation of the proteins. An unbuffered 3.5 % (final cone.) NaCl solution was found to be highly effective and gave consistent results and lower blank values. Incorporation rates obtained with our protocol showed good agreement with the commonly used filtration method. Therefore, we argue that for freshwater samples an NaCl or humic extract addition is necessary for an efficient precipitation of the proteins when the centrifugation method for determining bacterial secondary production via H-3-leucine incorporation is applied.
April 1999
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63 Reads
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32 Citations
Aquatic Microbial Ecology
In an investigation in the backwater system of the Alte Donau (Vienna, Austria) on the impact of heterotrophic nanoflagellates (HNF) as bacterivores and on their role in the pelagic carbon cycle, it was shown that from April 1995 to dune 1996, HNF abundance ranged from 0.2 x 10(2) to 39.2 x 10(2) cells ml(-1), with a yearly mean of 5.8 x 10(2) cells ml(-1). Mean HNF biomass was 7.4 mu g C l(-1), ranging from 0.1 to 41.1 mu g C l(-1). Ingestion rates on heterotrophic bacteria, estimated on the basis of uptake of fluorescently labeled bacteria, were 2.2 to 26.5 cells HNF-1 h(-1) (mean: 7.5 cells HNF-1 h(-1)). Resulting grazing rates only made up between 0.3 and 20 % (mean: 5 %) of bacterial secondary production, and it was evident that heterotrophic nanoflagellates were not able to control bacterial production, indicating that factors other than HNF grazing must play an important role for the mortality of bacteria in the investigated system. A consequence of the fact that only a mean of 0.09 mu g bacterial carbon l(-1) h(-1) was consumed by HNF was that transfer of picoplanktonic carbon to higher trophic levels via HNF was negligible. HNF could not function as a link between the microbial compartment and the classical pelagic food chain, even if nanoflagellates themselves were under strong predatory control, which was indicated by experiments conducted to compare flagellate gross and net growth rates. Another finding was that HNF covered only a mean of 21 % of their carbon demand by the consumption of bacteria, despite high abundance of bacterial carbon as a food source. The error potential of the applied methods was estimated in view of the carbon budget of the bacteria-HNF interaction. This still implied that HNF had to use other carbon sources to a remarkable degree in order to maintain production. The possibility that dissolved organic matter (DOM) may represent a major energy source covering HNF carbon demand is discussed.
... Patterns of microbial faecal pollution and pollution hotspots were identified from the headwaters in Germany to the Danube River Delta shortly before entering the Black Sea (Kavka and Poetsch 2002). Thereafter, the JDS was organised every 6 years in 2007 (JDS2), 2013 (JDS3) and 2019 (JDS4) (ICPDR 2008(ICPDR , 2015(ICPDR , 2021b including the assessment of microbial faecal pollution (Kirschner et al. 2015a(Kirschner et al. , 2008(Kirschner et al. , 2009(Kirschner et al. , 2017. ...
January 2008
... Infant botulism in birds is also described (Miyazaki and Sakaguchi 1978). Avian outbreaks have been linked to wetland sediments (Zechmeister et al. 2005) and ...
January 2005
ALTEX: Alternativen zu Tierexperimenten
... Leucine incorporation and bacterial production -Bacterial 3 H-leucine incorporation (LI) was measured based on protocols of Kirschner and Velimirov (1999). Briefly, 3 H-leucine (4.4 TBq mmol -1 , ARC Research Products, USA) was added to triplicate 10 mL samples at a final concentration of 10 nmol L -1 . ...
May 1999
Aquatic Microbial Ecology
... To avoid instrument clogging, sediment samples must be centrifuged before determined by FCM, such a process could lead to underestimation and higher coefficient of variation of the enumeration (Glud and Middelboe, 2004;Siem-Jørgensen et al., 2008;Dai, 2012;Frossard et al., 2016). Currently, EFM is still the most widely used procedure for counting sediment viruses and prokaryotes, and it has been continuously optimized in the past decades of this century (Danovaro et al., 2001;Fischer et al., 2005;Helton et al., 2006;Dell'Anno et al., 2009;Danovaro and Middelboe, 2010;Suttle and Fuhrman, 2010). ...
October 2005
Aquatic Microbial Ecology
... Although HF and ciliates are considered the main grazers of bacterioplankton (Sanders et al. 1992;Callieri et al. 2002;Zingel et al. 2007), the absence of relationship between protists and HB is frequently found in ecological studies (Wieltschnig et al. 2001;Comte et al. 2006;Fermani et al. 2013). One explanation is the use of alternative food resources (Wieltschnig et al. 1999), mainly in the tropics, where heterotrophic bacteria convert more carbon into CO 2 and less into available biomass to higher trophic levels (Amado et al. 2013). ...
April 1999
Aquatic Microbial Ecology
... In Austrian part of River Danube, the concentrations of some nutrients were minimum in summer and maximum in winter (Weilguni and Humpesch 1999). A succession of phytoplankton dominant turbid water from macrophyte dominant clear water state in eutrophic back water of river Denube was recorded between 1992 and 1994 (Kirschner et al. 1999). ...
June 1999
Aquatic Microbial Ecology