Biomedical subjects

B Riemann

Publications and source records attributed to B Riemann.

24 records · Page 2Linked to original sources

PubMed1990

Effects of toxic substances on natural bacterial assemblages determined by means of [h]thymidine incorporation.

The effects of 3,5-dichlorophenol, 2,4-dinitrophenol, and potassium dichromate on natural bacterial assemblages were examined by means of [H]thymidine incorporation into trichloroacetic acid-insoluble material. Results from a large number of coastal marine and freshwater samples suggest the following. (i) The effects of the three toxicants included reductions in the bacterial cell number as well as changes in rates of [H]thymidine incorporation and in [H]thymidine incorporation per cell. The concentrations that inhibited [H]thymidine incorporation by 50% ranged from 3 to 11 mg liter for 3,5-dichlorophenol, 6 to 10 mg liter for 2,4-dinitrophenol, and 21 to 123 mg liter for potassium dichromate, with a tendency to higher values in bacterial assemblages from more eutrophic environments. (ii) The effects of 3,5-dichlorophenol and potassium dichromate determined by [H]leucine incorporation into bacterial protein were similar or larger than those obtained from [H]thymidine incorporation. (iii) Two to four hours of exposure to the toxicants was necessary before stable maximum effects were found in [H]thymidine incorporation. (iv) Storage of natural environmental samples should be avoided, since tests with water stored for 1 to 3 days sometimes produced results different from results obtained from in situ tests. (v) The effects of 3,5-dichlorophenol, 2,4-dinitrophenol, and potassium dichromate on natural bacterial assemblages were relatively constant during periods with different growth rates in the assemblages, during various periods of the year, and between samples from freshwater and marine localities. With some precautions, [H]thymidine incorporation can be used as a quick and sensitive method for determining the effects of toxicants on aquatic bacterial assemblages from natural environmental samples.

Journal Article↗

PubMed1989

Regulation of bacterioplankton production and cell volume in a eutrophic estuary.

During three periods of 16 to 25 days, bacterioplankton production, bacterial cell volume, chlorophyll a, CO(2) assimilation, and particulate organic carbon were measured in enclosures situated in the eutrophic estuary Roskilde Fjord, Denmark. The enclosures were manipulated with respect to sediment contact and contents of inorganic nutrients, planktivorous fish, and suspension-feeding bivalves. Nutrient enrichment, the presence of suspension feeders, and sediment contact induced pronounced changes in bacterial production, as well as minor changes in bacterial cell volume; however, these effects seemed to be indirect, transmitted via phytoplankton. Bacterial production, measured as [H]thymidine incorporation, closely followed changes in phytoplankton biomass and production, with time lags of 5 to 10 days. Good correlations of mean bacterioplankton production to chlorophyll a concentration and CO(2) assimilation suggested phytoplankton to be the dominating source of bacterial substrate, apparently independent of nutrient stress. Zooplankton >140 mum, bivalves, and sediment seemed to provide insignificant, if any, substrate for bacterioplankton, and benthic suspension feeders seemed not to act as direct competitors for dissolved organic carbon. The bacterioplankton mean cell volume, measured by image analysis, changed seasonally, with the smallest cells during the summer. Within each period, the bacterial cell volume correlated positively to growth rate and negatively to temperature.

Journal Article↗

PubMed1988

Calculation of cell production from [h]thymidine incorporation with freshwater bacteria.

The conversion factor for the calculation of bacterial production from rates of [H]thymidine incorporation was examined with diluted batch cultures of freshwater bacteria. Natural bacterial assemblages were grown in aged, normal, and enriched media at 10 to 20 degrees C. The generation time during 101 growth cycles covered a range from 4 to >200 h. The average conversion factor was 2.15 x 10 cells mol of thymidine incorporated into the trichloroacetic acid (TCA) precipitate (standard error = 0.29 x 10; n = 54), when the generation time exceeded 20 h. At generation times of <20 h, the average conversion factor was 11.8 x 10 cells mol of thymidine incorporated into TCA precipitate (standard error = 1.72 x 10; n = 47). The amount of radioactivity in purified DNA increased with decreasing generation time and increasing conversion factor (calculated from the TCA precipitate), corresponding to a decrease in the percentage in protein. The conversion factors calculated from purified DNA or from the TCA precipitate gave the same variability. Conversion factors did not change significantly with the medium, but were significantly higher at 20 degrees C than at 15 and 10 degrees C. A detailed examination of the [H]thymidine concentrations that were needed to achieve maximum labeling in DNA was carried out 6 times during a complete growth cycle. During periods with low generation times and high conversion factors, 15 nM [H]thymidine was enough for the maximum labeling of the TCA precipitate. This suggests that incorporation of [H]thymidine into DNA is probably limited by uptake during periods with generation times of <20 h and that freshwater bacterioplankton cell production sometimes is underestimated when a conversion factor of 2.15 x 10 cells mol of thymidine incorporated is used.

Journal Article↗

PubMed1985

Potential importance of fish predation and zooplankton grazing on natural populations of freshwater bacteria.

The rates of ingestion of natural bacterial assemblages by natural populations of zooplankton (>50 mum in size) were measured during a 19-day period in eutrophic Frederiksborg Slotssø, Denmark, as well as in experimental enclosures (containing 5.3 m of lake water). The fish and nutrients of the enclosures were manipulated. In enclosures without fish, large increases in ingestion by zooplankton >140 mum in size were found (up to 3 mug of C liter h), compared with values less than 0.3 mug of C liter h in the enclosures with fish and in the open lake. Daphnia cucullata and D. galeata dominated the community of zooplankton of >140 mum. Ingestion rates for zooplankton between 50 and 140 mum decreased after a period of about 8 days, in all enclosures and in the lake, to values below 0.1 mug of C liter h. On the last 2 sampling days, somewhat higher values were observed in the enclosures with fish present. The >50-mum zooplankton ingested 48 to 51% of the bacterial net secondary production in enclosures without fish, compared to 4% in the enclosures with added fish. Considering the sum of bacterial secondary production plus biomass change, 35 to 41% of the available bacteria were ingested by zooplankton of >50 mum in the enclosures without fish, compared with 4 to 6% in the enclosures with added fish and 21% in the open lake. Fish predation reduced the occurrence of zookplankton sized >50 mum and thus left a large proportion of the available bacteria to zooplankton sized <50 mum. In fact, there were 4.6 x 10 to 5.0 x 10 flagellates (4 to 8 mum in size) ml in the enclosures with fish added as well as in the lake, compared with 0.5 x 10 to 2.3 x 10 ml in the enclosures without fish. This link in the food chain was reduced when fish predation on zooplankton was eliminated and a direct route of dissolved organic matter, via the bacteria to the zooplankton, was established.

Journal Article↗

PubMed1984

Measurements of diel rates of bacterial secondary production in aquatic environments.

Measurements of bacterial secondary production were carried out during 13 diel studies at one coastal marine station and in five lakes differing with respect to nutrient concentration and primary production. Bacterial secondary production was measured in situ every 3 to 5 h by [H]thymidine incorporation into DNA. In some of the diel studies, these results were compared with results obtained from dark CO(2) uptake and frequency of dividing cells. Only minor diel changes were observed. The rate of [H]thymidine incorporation into DNA and the frequency of dividing cells varied from 23 to 194% of the diel mean. The dark CO(2) uptake rate varied from 12 to 259% of the diel mean. An analysis of variance demonstrated that no specific time periods during 24 h showed significantly different production rates, supporting the idea that bacterial activities in natural assemblages are controlled by a variety of events. The best correction (r = 0.74) was obtained between the [H]thymidine incorporation and frequency of dividing cells procedures from the lake water samples. The actual production rates calculated by [H]thymidine incorporation into DNA were appreciably lower than those obtained by the frequency of dividing cells and the dark CO(2) uptake techniques. Diel rates of bacterial production are discussed in relation to sampling frequency, statistical errors, and choice of method.

Journal Article↗

PubMedDate not supplied

Monitoring tumor activity in low grade glioma of childhood.

Chemotherapeutic or radiotherapeutic regimens are being increasingly used in low grade glioma of childhood. These protocols require methods to monitor tumor activity. We report our experience in eleven patients. The tumors were localized in the optic pathway (3), cerebral cortex (4) and thalamus/hypothalamus (4). Histological diagnoses included low grade astrocytoma (6), gliofibroma (1) and ganglioglioma (2). Two children with neurofibromatosis type 1 (NF-1) and typical optical tumors were not biopsied. 13 episodes of progression were noted including 3 altered diagnoses. This was evident from clinical symptoms in 11/13 episodes, computed tomography (CT) or magnetic resonance imaging (MRI) in 10/13 situations, iodine-123-alpha-methyltyrosine (123I-IMT) single-photon emission computed tomography (SPECT) in 10/10 situations, fluorine-18 fluorodesoxyglucose (18F-FDG) positron emission tomography (PET) in 0/3 and thallium-201 (201Tl) SPECT in 1/1. Seven responses to chemotherapy were recorded. Clinical symptoms indicated this in 7/7 situations, MRI in 5/7, 123I-IMT SPECT in 1/2 and 201Tl SPECT in 1/1. These data suggest that 123I-IMT SPECT is a valuable addition to low grade glioma diagnostic and stress the need for a prospective study.

Adolescent↗