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191.
The relation between net dimethyl sulfide (DMS) production and changes in near surface (0-5 mm) oxygen concentrations in a sea grass (Zostera noltii Hornem)-covered intertidal sediment ecosystem was examined during a diel cycle. Sediment covered with Zostera was found to be more oxygenated than uncovered sediment during the period of photosynthesis. This phenomenon was probably caused by radial oxygen loss of the Zostera root-rhizome system. The population sizes of the three functional groups of microbes mainly responsible for the concentration of DMS, the dimethylsulfoniopropionate (DMSP)-demethylating, DMSP-cleaving and DMS-oxidizing bacteria, were quantified by most probable number (MPN) methodologies. Sediments with Zostera supported substantially higher populations of both aerobic (149x10(6) cm(-3) DMSP-utilizing and 0.4x10(6) cm(-3) DMS-oxidizing) and anaerobic (43x10(6) cm(-3) DMSP-utilizing and 0.4x10(6) cm(-3) DMS-oxidizing) microorganisms than sediments without Zostera (DMSP-utilizing aerobes and anaerobes both 2x10(6) cm(-3) and DMS-oxidizing aerobes and anaerobes both 0.2x10(6) cm(-3)). Experiments conducted with sediment cores and sediment slurries suggested that the net production of DMS in these sediments was significantly lower during oxic periods than during anoxic periods. Intact sediment cores with and without Zostera produced DMS when incubated under anoxic/dark conditions (97.0 and 53.6 nmol DMS m(-2) h(-1), respectively), while oxic/light-incubated cores did not produce detectable amounts of DMS. In addition, kinetic parameter values (V(max) and K(m)) for DMSP degradation in cell suspensions of isolated DMSP-demethylating and DMSP-cleaving bacteria were measured and compared to documented values for other strains. Both V(max) and K(m) values for DMSP-demethylating organisms were found to be relatively low (14.4-20.1 nmol DMSP mg protein(-1) min(-1) and 4.1-15.5 μM, respectively) while these parameter values varied widely in the group of the DMSP-cleaving organisms (6.7-1000 nmol DMSP mg protein(-1) min(-1) and 2-2000 μM, respectively). It was hypothesized that a diel rhythm in DMS emission occurred, with a relatively low net production during the day and a high net production during the night. Environmental changes which result in increased anoxic conditions in coastal sediments, such as an increase in eutrophication, may therefore result in increased atmospheric DMS emission rates. 相似文献
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PCR-based assays of mendelian polymorphisms from anonymous single-copy nuclear DNA: techniques and applications for population genetics 总被引:5,自引:0,他引:5
This paper outlines a PCR-based approach for population genetics that
offers several advantages over conventional Southern blotting methods for
revealing restriction-fragment-length polymorphisms (RFLPs) in nuclear DNA.
Primers are constructed from clones isolated from a nuclear DNA library,
and these primers subsequently are employed in in vitro syntheses of
homologous regions. Amplified products are then screened directly for RFLPs
by using gel-staining procedures. Population applications for this
PCR-based approach, including potential strengths and weaknesses, are
exemplified by two RFLP data sets generated to estimate (a) male-mediated
gene flow in the green turtle (Chelonia mydas) and (b) geographic
population genetic structure in the American oyster (Crassostrea
virginica). Restriction assays of amplified products from 14 or 15
independent primer pairs in each species revealed polymorphisms at several
loci that proved highly informative in the population genetic analyses. In
general, the Mendelian polymorphisms produced by this PCR-based approach
will provide useful genetic markers for population studies, particularly in
situations where simpler and less expensive allozyme methods have failed,
for whatever reason, to provide adequate information.
相似文献
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Nowakowski AM Stangel M Grupp TM Valderrabano V 《Journal of applied biomaterials & functional materials》2012,10(2):e127-e135
Purpose: The important roles of the anterior cruciate ligament regarding knee stability, physiologic kinematics, and proprioception are unquestioned. Thus, various efforts have been made to retain the ACL during total knee arthroplasty (TKA). Neither of the existing solutions to this problem, i.e. bicruciate retaining prostheses and implantation of two unicondylar prostheses, has been successful because of concept-specific problems as well as general difficulties with implant fixation.?The new transversal support tibial plateau concept is a prosthesis of two individual joint surfaces reinforced beneath the articular line by joint surface supports and buttressed by a single transversal support. This configuration, which enables retention of both cruciate ligaments, should provide good bone fixation and ensure long-term alignment of the individual joint surfaces. Methods: In the current study, four prototypes based on this novel concept were developed and the resulting primary stability was analyzed using adapted load testing. The test set-up, with the model-loading of specially prepared Sawbones? and a sinusoidal oscillating load transmission with 25 000 cycles over 10 increasing load levels, achieved subsidence, which enabled comparison of the four different model variants regarding primary stability in view of bone anchoring.Results: The model variant (TSmobile) that allowed transverse glide of the joint surface supports along the transversal support revealed the largest subsidence.Conclusions: A rigid attachment of the joint surface supports of the transversal support tibial plateau thus appears to offer increased primary stability regarding bone anchoring. 相似文献
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Donald SA McLeod 《The Clinical biochemist. Reviews / Australian Association of Clinical Biochemists》2010,31(1):9-19
This paper provides an overview on the biology, monitoring and management of differentiated thyroid cancer (DTC), with particular attention to issues of relevance to clinical chemistry. The incidence of DTC appears to be increasing and management strategies are evolving as we learn more about its natural history and response to therapy. Clinical chemistry techniques play a central role in these protocols. Technical limitations inherent in current monitoring tools can hamper follow-up, although progress is being made. The molecular basis of DTC is being delineated with the potential to develop new strategies for diagnosis, monitoring and management of this condition. 相似文献