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281.
Matthieu Amor François P. Mathon Caroline L. Monteil Vincent Busigny Christopher T. Lefevre 《Environmental microbiology》2020,22(9):3611-3632
Magnetotactic bacteria (MTB) are ubiquitous aquatic microorganisms that incorporate iron from their environment to synthesize intracellular nanoparticles of magnetite (Fe3O4) or greigite (Fe3S4) in a genetically controlled manner. Magnetite and greigite magnetic phases allow MTB to swim towards redox transition zones where they thrive. MTB may represent some of the oldest microorganisms capable of synthesizing minerals on Earth and have been proposed to significantly impact the iron biogeochemical cycle by immobilizing soluble iron into crystals that subsequently fossilize in sedimentary rocks. In the present article, we describe the distribution of MTB in the environment and discuss the possible function of the magnetite and greigite nanoparticles. We then provide an overview of the chemical mechanisms leading to iron mineralization in MTB. Finally, we update the methods used for the detection of MTB crystals in sedimentary rocks and present their occurrences in the geological record. 相似文献
282.
The reproduction of Nereid Perinereis cultrifera in the English Channel and the Atlantic is of an epitokous type. The same Nereid in the Mediterranean (Bay of Alger) has been described as atokous (Marcel, 1962) and since that time epitoky in mediterranean specimens has been considered to be an accidental phenomenon. However, in the present study polychaetes collected at Salammb? (near Tunis) show that those P. cultrifera reproduce exclusively by epitoky. 相似文献
283.
The authors studied the sperm features of 122 patients, before and 3 months, 6 months, 9 months and 12 months after varicocele repair, in order to define the sperm profiles of these patients and to study effects of this treatment on these profiles. Patients with varicocele generally present severe asthenozoospermia. Of the 122 patients studied: ?18% were extreme oligozoospermic, ?26% were severe oligozoospermic, ?18% were moderate oligozoospermic, ?38% were normozoospermic. Varicocele repair does not influence the volume of semen, the vitality of spermatozoa, their survival, their rate of abnormal shapes, or male genital tract markers, but significantly improves sperm counts and mobility, in men with extreme or severe oligozoospermia. This type of treatment is generally indicated in patients with extreme or severe oligoasthenozoospermia in order to obtain a natural pregnancy, or at least to increase the success of medically assisted procreation techniques. 相似文献