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321.
A method was developed to detect fewer than 100 CFU of campylobacteria from SIFF transport medium to which thawing drip from deep frozen broiler carcasses was added as a source of contamination and which was then stored at room temperature for 20 h. The method was made possible by using pre–enrichment in 1 % buffered peptone water under a microaerophilic atmosphere for 5 h at 43°C before selective enrichment either in brucella enrichment broth and on brucella blood selective agar supplemented with Skirrow antibiotics or in CCD enrichment broth and on blood free CCD selective agar. The other pre–enrichment broth studied was alkaline peptone water with reducing agents (RAPW) and the other enrichment broths and selective agars were Preston broth and agar, THAL broth and alkaline tryptose broth (ATB) and brucella agar with ATB antibiotics. Contaminating flora can be a problem when using enrichment broths and selective agars with limited antibiotic supplementation. 相似文献
322.
The effects of slow (apatite, biotite) and fast-release nutrients (P, K, Mg) on C and N mineralization in acid forest soil
were studied. These nutrients were applied alone or together with urea or urea and limestone. The production of CO2 in the soil samples taken one and three growing seasons after the application was lower in the soils treated with the fast-release
nutrients than in the untreated soils. Similar reduction of microbial activity was not seen after the apatite and apatite+biotite
treatments. In the first growing season, urea and urea+limestone enhanced CO2 production, but after three growing seasons, the opposite was true. Apatite and apatite+biotite added together with urea
did not compensate for the decreasing effect of urea on the CO2 production. The addition of fast-release salts increased somewhat the concentration of NH
inf4
sup+
in the soil and more NH4
+ accumulated during laboratory incubation in the soil samples taken one growing season after the application. The urea addition
immediately increased the concentrations of NH4
+ and of NO3
− in the soil, but, three growing seasons after application, urea had only a slight increasing effect on mineral N content
of the soil. Slow-release nutrients seem to have a more favourable effect than fast-release salts on nutrient turnover in
acid forest soil. 相似文献
323.
324.
Six Campylobacter jejuni and six Campylobacter coli strains were isolated from cows and pigs, and their survival in lake water was compared by viable counts. Campylobacter jejuni survived longer in culturable form than C. coli in untreated and membrane-filtered water both at 4 and 20 degrees C. This difference in survival time may be a reason why C. jejuni is generally isolated from surface waters more frequently than C. coli. Both species survived better in filtered than in untreated water. This suggests that predation and competition for nutrients affect the survival of both Campylobacter species in the aquatic environment. 相似文献
325.
Variations in the thymidine incorporation rate, bacterial abundance, and mean cell volumes in the surface water (0.5 m) of the Baltic Sea in spring and summer were compared in studies with different spatial scales (570 nautical miles [nmi] [ca. 1056 km], 220 nmi [ca. 407 km], 24 nmi [ca. 44 km], 12 nmi [ca. 22 km], and 200 m). The objective of the comparison was to investigate whether a single sample taken at one sampling point is representative enough for researchers to make generalizations about a larger water area. Bacterioplankton variation was connected more to seasonal characteristics than to the spatial scale of sampling. Variation was greater and more random in spring than in summer. The state variables (bacterial abundance and mean cell volume) varied less than the rate variable (thymidine incorporation). The results suggest that the sampling design for bacterioplankton studies in northern temperate seas should be planned primarily according to the season and that more stress should be put on rate variable measurements than on those of state variables. 相似文献
326.
E. Olavi Kajander Rauno J. Harvima Terho O. Eloranta Heli Martikainen Marjatta Kantola Sirpa O. Kärenlampi Kari Åkerman 《Biological trace element research》1991,28(1):57-68
Selenomethionine metabolism and the biochemical basis for its cytotoxicity were analyzed in cultured human and murine lymphoid cells. The metabolic pathways were also addressed, using purified mammalian enzymes and crude tissue extracts. Selenomethionine was found to be effectively metabolized to S-adenosylmethionine analog, and that analog was further metabolized in transmethylation reactions and in polyamine synthesis, similarly to the corresponding sulphur metabolites of methionine. Selenomethionine did not block these pathways, nor was there a specific block on the synthesis of DNA, RNA, or proteins when added to the culture medium. Selenomethionine showed cytotoxicity at above 40 microM levels. Yet, low selenomethionine levels (10 microM) could replace methionine and support cell growth in the absence of methionine. Selenomethionine toxicity took place concomitantly with changes in S-adenosylmethionine pools. D-form was less cytotoxic than L-form. Methionine concentration modified the cytotoxicity. Together, this indicates that selenomethionine uptake and enzymic metabolism are involved in the cytotoxicity in a yet unknown way. 相似文献
327.
S Laitinen A Nevalainen M Kotimaa J Liesivuori P J Martikainen 《Applied and environmental microbiology》1992,58(11):3774-3776
The relationship between bacterial counts and endotoxin concentrations in air samples was studied. Selective EMB medium favored the growth of a larger portion of airborne gram-negative bacteria than LES Endo or MacConkey medium and was a good predictor of the endotoxin levels determined with a chromogenic Limulus assay of the air of wastewater treatment plants. The bacterial counts determined with nonselective media correlated poorly with airborne endotoxin levels; however, R2A medium yielded higher viable bacterial counts than TYG medium. Direct counting by epifluorescence microscopy yielded the highest bacterial counts, but no correlation was obtained between total bacterial counts and endotoxin concentrations. 相似文献
328.
Summary We have studied bottom-up and top-down control of the Southern Ocean microbial food web by microcosm experiments. Water from the Weddell Sea and Weddell Scotia Confluence were used for the experiments. Microcosms were manipulated by nutrients and light, and by size-selective screening. Incubation at the higher light level doubled phytoplankton growth rates from 0.12 to 0.24 day–1 in the Weddell experiment and from 0.15 to 0.30 day–1 in the Confluence experiment. Nutrient enrichment had no significant effect on growth rates in either of the experiments, indicating that phytoplankton growth was not nutrient-limited. In the microcosms where dinoflagellate growth rate was different, high dinoflagellate numbers were reflected as depressed nanoflagellate growth as well as depressed growth of phytoplankton, suggesting that dinoflagellates controlled both heterotrophic nanoflagellates and autotrophic nanoplankton. Only during short periods, when dinoflagellate numbers were low, could exponential growth of nanoflagellates be demonstrated. Bacterioplankton growth rates were, on average, 0.26 day–1 in the Weddell experiment and 0.22 day–1 in the Confluence experiment. Bacteria were controlled by heterotrophic nanoflagellates. Potential growth rates up to 0.75 day–1 were measured from batch cultures without predators. With the microcosm experiments, we could demonstrate a strong top-down control by dinoflagellates on phytoplankton and on heterotrophic nanoflagellates, and a control by heterotrophic nanoflagellates on bacteria. We could also demonstrate weak nutrient limitation on autotrophs and substrate limitation on heterotrophic bacteria. In the two study areas, biomass production and carbon flow were mediated mainly by organisms that passed through a 20 m net and had growth rates in the order of 0.20 to 0.30 day–1.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation 相似文献
329.
330.
Four commonly used techniques for preparation of 14C-labeled algal samples on membranes for liquid scintillation counting were compared and a simple technique for apparent net assimilation measurement from aqueous samples was introduced. All four techniques yielded similar radioactivities from the test cultures and are thus suitable for measurements of 14C algal samples. The possibly carcinogenic solvent dioxane was not necessary with PCS scintillation cocktail for dissolving radioactivity from algae on filters. 相似文献