The colony-forming ability of long (3–9 months) incubated cystlike resting cells (CRC) of the nonspore-forming gram-positive bacteria Micrococcus luteus and Arthrobacter globiformis was studied in this work. The preservation of the CRC proliferative potential as assayed by plating on standard LB agar was shown to depend on the conditions of the formation of the dormant cells. In aged post-stationary cultures of micrococci and arthrobacters grown under carbon and phosphorus limitation the number of colony-forming units (CFU/ml) of CRC decreased in the course of 3–9 month incubation to the level of 106–107 CFU/ml. However, M. luteus CRC obtained under carbon and nitrogen limitation and A. globiformis CRC obtained under nitrogen limitation and starvation completely lost their ability to form colonies on standard solid medium after 4–6 months of incubation and turned into a ‘non-culturable’ (non-platable) state. In this case, the ratio of live cells in the population of M. luteus and A. globiformis ‘non-culturable’ CRCs (determined by the Live/Dead staining test) was 10–44% of the total cell number. To study the possible preservation of proliferative potential in non-platable CRCs, various methods of their reactivation were applied. Although preincubation of CRC suspensions in a buffer solution of 0.1 M K2HPO4 (pH 7.4) or in the presence of lysozyme (1 or 10 μg/ml) resulted in increased numbers of live cells (determined by the Live/Dead test) or in disruption of the cell conglomerates, it did not increase considerably the CFU titer on LB medium. Variations in the medium composition, such as addition of sodium pyruvate as an antioxidant or dilution of the medium, promoted the formation of macrocolonies by a small portion of nonplateable CRC of M. luteus (50?80 CFU/ml), whereas the number of the cells capable of microcolony formation (mCFU) was 1.8–6.8 × 105 mCFU/ml, exceeding the CFU titers by four orders of magnitude. The application of semisolid agar and the most probable number (MPN) method was the most efficient for determination of the mCFU titer, and an almost complete reversion of ‘non-culturable’ micrococcal CRCs to microcolony formation was observed (up to 2.3 × 107 mCFU/ml). The usefulness of diluted complete media for the restoration of the colony-forming ability of the dormant forms was confirmed in experiments with ‘nonculturable’ CRCs of A. globiformis. The development of special procedures and methods for determining actively proliferating cells not detected by ordinary methods is of great importance for advanced monitoring studies. 相似文献
Previous studies have shown that subunits E (eIF3e), F (eIF3f) and H (elF3h) of eukaryotic translation initiation factor 3 play important roles in cell development in humans and yeast. eIF3e and eIF3h have also been reported to be important for normal cell growth in Arabidopsis. However, the functions of subunit eIF3f remain largely unknown in plant species. Here we report characterization of mutants for the Arabidopsis eIF3f (AteIF3f) gene. AteIF3f encodes a protein that is highly expressed in pollen grains, developing embryos and root tips, and interacts with Arabidopsis eIF3e and eIF3h proteins. A Ds insertional mutation in AteIF3f disrupted pollen germination and embryo development. Expression of some of the genes that are essential for pollen tube growth and embryogenesis is down‐regulated in ateif3f‐1 homozygous seedlings obtained by pollen rescue. These results suggested that AteIF3f might play important roles in Arabidopsis cell growth and differentiation in combination with eIF3e and eIF3h. 相似文献
Selected methods recommended in national and international water quality guidelines were compared in tests on environmental waters with different levels of faecal pollution. The following methods yielded no statistically significant differences in counts of faecal coliforms and Escherichia coli in raw sewage, semi-treated effluent, polluted urban run-off and stored potable water: Membrane filtration (MF) using MFc Agar or Chromocult Coliform Agar containing X-glucuronide, or a miniaturised microtitre-plate Most Probable Number (MPN) assay using a liquid growth medium containing chromogenic 4-methyl-umbelliferyl--D-glucuronide. Significant differences were, however, found between the Chromocult and the other methods for unpolluted river water. Counts of faecal enterococci in raw sewage, semi-treated effluent and polluted urban run-off, obtained by the following methods did not differ significantly: MF using M-Enterococcus Agar, Bile-Esculin Agar or Enterococcus Selective Agar, or a microtitre-plate MPN method with a liquid growth medium containing chromogenic 4-methyl-umbelliferyl--D-glucoside. Significant differences were, however, found between the MPN and the other methods for unpolluted river water and stored potable water. MF using Chromocult Coliform Agar had useful benefits for the simultaneous enumeration of coliforms and E coli. However, in view of cost and practical considerations, MF using MFc Agar or M-Enterococcus Agar proved the methods of choice for respectively enumerating faecal coliforms and E coli, or faecal enterococci, in analyses for general water quality surveillance purposes. 相似文献
The bias in the most-probable-number (MPN) estimate of microbial densities derived from serial dilutions might be less important than it has appeared to be. For many purposes, bias in the logarithm of the MPN is more important than bias in the MPN, and the bias in the logarithm is much less. The lesser bias has been reduced by using the theorems of Salama, Koch, and Tolley. Formulas and tables are provided. 相似文献
Background: As a consequence of climate warming, many organisms are shifting their range towards higher latitudes and altitudes. As not all do so at the same speed, this may disrupt biotic interaction. Release from natural enemies through range expansion can result in invasiveness, whereas loss of mutualists can reduce plant vigour and fitness. One of the most important groups of plant symbiotic mutualists is the arbuscular mycorrhizal fungi (AMF).
Aims: We used greenhouse experiments to test whether Tragopogon dubius, a species that has recently expanded its range northward and colonised the Netherlands, is able to associate with the same AMF as the native congener T. pratensis.
Methods: In soils collected from four locations in the new range of T. dubius we compared the density of infective AMF propagules associating with both plant species, as well as AMF colonisation of the roots. The AMF community structure in the roots of these species was also analysed using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE).
Results:Tragopogon dubius and T. pratensis did not differ in any of these characteristics.
Conclusions: We therefore conclude that the range-shifting T. dubius is as effective in the formation of mycorrhiza as the native congener. 相似文献
The importance of crustal fluid chemical composition in driving the marine deep subseafloor biosphere was examined in northeast Pacific ridge-flank sediments. At IODP Site U1301, sulfate from crustal fluids diffuses into overlying sediments, forming a transition zone where sulfate meets in situ-produced methane. Enhanced cell counts and metabolic activity suggest that sulfate stimulates microbial respiration, specifically anaerobic methane oxidation coupled to sulfate reduction. Cell counts and activity are also elevated in basement-near layers. Owing to the worldwide expansion of the crustal aquifer, we postulate that crustal fluids may fuel the marine deep subseafloor biosphere on a global scale. 相似文献
Mutations in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) are key events in the development of glioma, acute myeloid leukemia (AML), chondrosarcoma, intrahepatic cholangiocarcinoma (ICC), and angioimmunoblastic T-cell lymphoma. They also cause D-2-hydroxyglutaric aciduria and Ollier and Maffucci syndromes. IDH1/2 mutations are associated with prolonged survival in glioma and in ICC, but not in AML. The reason for this is unknown. In their wild-type forms, IDH1 and IDH2 convert isocitrate and NADP+ to α-ketoglutarate (αKG) and NADPH. Missense mutations in the active sites of these enzymes induce a neo-enzymatic reaction wherein NADPH reduces αKG to D-2-hydroxyglutarate (D-2HG). The resulting D-2HG accumulation leads to hypoxia-inducible factor 1α degradation, and changes in epigenetics and extracellular matrix homeostasis. Such mutations also imply less NADPH production capacity. Each of these effects could play a role in cancer formation. Here, we provide an overview of the literature and discuss which downstream molecular effects are likely to be the drivers of the oncogenic and survival-prolonging properties of IDH1/2 mutations. We discuss interactions between mutant IDH1/2 inhibitors and conventional therapies. Understanding of the biochemical consequences of IDH1/2 mutations in oncogenesis and survival prolongation will yield valuable information for rational therapy design: it will tell us which oncogenic processes should be blocked and which “survivalogenic” effects should be retained. 相似文献
Summary Inoculation of pearl millet (Pennisetum americanum (L.) Leeke) with Azospirillum significantly increased the numbers of this organism in the rhizosphere, rhizoplane, washed and crushed roots and surface sterilized and crushed roots. The maximum number of organisms plant–1 were localized in the rhizosphere. The numbers of Azospirillum on the roots of inoculated plants grown under sterilized conditions were much higher than in the field grown plants. In both cases populations outside the roots were higher than in the surface sterilized roots. The highest numbers per unit root weight were recorded between 60–75 days of growth. N2-ase activity throughout the growth cycle was very low and was not related to the populations of Azospirillum on the roots. Root exudates and extracts of pearl millet showed a stimulatory effect on the growth of Azospirillum suggesting their possible involvement in the colonization of this organism on the roots of inoculated plants. 相似文献