排序方式: 共有33条查询结果,搜索用时 656 毫秒
1.
2.
3.
For 3 years aspects of the population dynamics, growth, and bioactivity (measure of biologically active metabolite biosynthesis) of the Demospongiae Latrunculia sp. nov. and Polymastia croceus (Kelly‐Borges & Bergquist) were examined on a subtidal reef on the Wellington south coast, New Zealand. For both species, survival of adult sponges was high in all seasons, whereas juvenile sponges had poor survival. Recruitment of Latrunculia sp. nov. occurred in all seasons indicating that this species is reproductively active throughout the year. P. croceus recruited mostly in autumn, supporting previous work that found the sponge to be reproductively active in summer and early autumn only. For both sponge species, growth rates varied greatly between individuals and were unaffected by initial sponge size within the range examined. Sponges generally grew during winter and spring as the water temperature rose, and shrank during summer and autumn as the water temperature fell. This growth pattern may relate to seasonal variation in food abundance, and for P. croceus it may result also from seasonal differences in reproductive investment. After 2 years, Latrunculia sp. nov. and P. croceus had on average, halved and doubled in size, respectively. Latrunculia sp. nov. showed a seasonal pattern of bioactivity, being most active in spring possibly to prevent the surface overgrowth of fouling organisms. P. croceus had no seasonal pattern of bioactivity, but individuals were either very active or inactive. The bioactive metabolites in both species possibly aid in competitive interactions and prevent predation and biofouling. 相似文献
4.
The mechanisms controlling microbial uptake of FeIII-siderophore complexes and subsequent release of the metal for cellular use have been extensively studied in recent years. Reduction of the FeIII center is believed to be necessary to labilize the coordinated Fe and facilitate exchange with cellular ligands. Previous studies report reduction of FeIII-DFOB by various reducing agents in solutions containing FeII-chelating colorimetric agents for monitoring reaction progress, but the importance of these findings is unclear because the colorimetric agents themselves stabilize and enhance the reactions being monitored. This study examines the reduction of FeIII complexes with DFOB (desferrioxamine B), a trihydroxamate siderophore, by the fully reduced hydroquinone form of flavin mononucleotide (FMNHQ) in the absence of strong FeII-chelating agents, and Fe redox cycling in solutions containing DFOB and oxidized and reduced FMN species. Experimental results demonstrate that the rate and extent of FeIII-DFOB reduction is strongly dependent on pH and FMNHQ concentration. At pH ? 5, incomplete FeIII reduction is observed due to two processes that re-oxidize FeII, namely, the autodecomposition of FeII-DFOB complexes (FeII oxidation is coupled with reduction of a protonated hydroxamate moiety) and reaction of FeII-DFOB complexes with the fully oxidized flavin mononucleotide product (FMNOX). Chemical speciation-dependent kinetic models for the forward reduction process and both reverse FeII oxidation processes are developed, and coupling kinetic models for all three Fe redox processes leads to successful predictions of steady-state FeII concentrations observed over a range of pH conditions in the presence of excess FMNHQ and FMNOX. The observed redox reactions are also in agreement with thermodynamic constraints imposed by the combination of FeIII/FeII and FMNOX/FMNHQ redox couples. Quantitative comparison between kinetic trends and changing Fe speciation reveals that FMN species react predominantly with diprotonated FeIII-DFOB and FeII-DFOB complexes, where protonation of one hydroxamate group opens up two Fe coordination positions. This finding suggests that ternary complex formation (FMN-Fe-DFOB) facilitates inner-sphere electron transfer reactions between the flavin and Fe center. 相似文献
5.
6.
7.
The instruments developed and operational experience gained in the measurement of strain rates and stresses in floating sea ice are described to indicate the total global loads occurring naturally against an artificial island or similar structure. A delta strainmeter and a thin-disk stress sensor were developed to service particular measurement needs for which suitable equipment was not available. The loading conditions studied have included slow-moving winter first-year ice at Tarsiut, Mukluk, and Kaubvik Islands in the Beaufort Sea, freely moving summer multiyear ice at Hans Island, and a pack-ice mixture at Katie's Floeberg. The instruments have also been deployed on a surging glacier on Spitzbergen in Norway 相似文献
8.
9.
10.
Verst Rowena Lieske Wolfgang Baille Wiebke Pulsfort Matthias Wichtmann Torsten 《Acta Geotechnica》2022,17(2):497-510
Acta Geotechnica - The increasing use of polymer solutions as support fluids in pile drilling, diaphragm walling or tunnelling applications demands a more detailed discussion of their penetration... 相似文献