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1.
The growth and methane formation ofMethanospirillum hungatei were inhibited by an inhibitor of Na+/H+ antiport amiloride. After addition of NaCl or LiCl, when the cells had a lower intracellular pH and were deenergized, they
extruded protons into the external medium. The acidification of the external medium was stimulated by protonophores and inhibited
by amiloride. These findings suggest the existence of an Na+/H+ antiport in the cytoplasmic membrane ofM. hungatei and its role in the energetics of methanogenic bacteria. 相似文献
2.
Milan M. Ćirković 《Biology & philosophy》2014,29(4):539-557
The well-known argument against the Search for ExtraTerrestrial Intelligence (SETI) due to George Gaylord Simpson is re-analyzed almost half a century later, in the light of our improved understanding of preconditions for the emergence of life and intelligence brought about by the ongoing “astrobiological revolution”. Simpson’s argument has been enormously influential, in particular in biological circles, and it arguably fueled the most serious opposition to SETI programmes and their funding. I argue that both proponents and opponents of Simpson’s argument have occasionally mispresented its core content. Proponents often oversimplify it as just another consequence of biological contingency, thus leaving their position open to general arguments limiting the scope of contingency in evolution (such as the recent argument of Geerat Vermeij based on selection effects in the fossil record). They also tend to neglect that the argument has been presented as essentially atemporal, while referring to entities and processes that are likely to change over time; this has become even less justifiable as our astrobiological knowledge increased in recent years. Opponents have failed to see that the weaknesses in Simpson’s position could be removed by restructuring of the argument; I suggest one way of such restructuring, envisioned long ago in the fictional context by Stanislaw Lem. While no firm consensus has emerged on the validity of Simpson’s argument so far, I suggest that, contrary to the original motivation, today it is less an anti-SETI argument, and more an astrobiological research programme. In this research programme, SETI could be generalized into a platform for testing some of the deepest assumptions about evolutionary continuity and the relative role of contingency versus convergence on unprecedented spatial and temporal scales. 相似文献
3.
A tetrazolium-based microphotometric method has been devised for the determination of structure-bound dehydrogenase activities
with correction for nothing-dehydrogenase artefacts. The method is based on the microphotometric recording of maximum reaction
rates in a simple incubation chamber and consists of two successive measurements on the same section, the first in the absence
and the second in the presence of the substrate. Following the first measurement, the substrate-free medium is quickly exchanged
with the substrate-containing medium and a second measurement is taken. Subtraction of the first from the second reaction
rate yields the enzyme activity corrected for nothing-dehydrogenase. Measurements of succinate dehydrogenase (SDH) in skeletal
muscle fibres, liver, cardiac atrium and ventricle demonstrate the feasibility of the method. Measurements on the extensor
digitorum longus muscle of rat reveal a range of up to fivefold differences in SDH activity within the fibre population of
this muscle.
Accepted: 11 April 1997 相似文献
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We studied 630 bacterial strains isolated from surface waters and determined as enterococci on the basis of their growth on
Slanetz-Bartley agar in typical colonies. The strains were tested and characterized by several key conventional tests for
basic differentiation of enterococci and by commercial test kits. We identified 135 strains ofE. fœcium (21%), 115E. fœcalis (18%), 30E. mundtii (5%), 27E. hirae (4%), 22E. casseliflavus (3%), 21E. gallinarum (3%), 17E. durans-E. hirae complex (3%), 5E. durans (1%), and 1 strain ofE. avium. 150 strains were classified only asEnterococcus sp. (25%) and 107 strains (17%) isolated from Slanetz-Bartley agar were not enterococci. We found that the non-enterococcal
group consisted of other Gram-positive cocci and Gram-positive and Gram-negative rods. Based on the identification we tried
to find a relation between taxonomic position of isolated strains and their colony morphology on Slanetz-Bartley agar. Out
of the total of 523 identified enterococci, 345 strains (66%) formed purple colonies, 136 red colonies (26%), 37 pink colonies
(7%) and 5 cream colored colonies (1%). There was no correlation among the color, size or colony morphology and the taxonomic
characterization of enterococcal strains. 相似文献
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Dr. Milan Šerko 《Plant Systematics and Evolution》1909,59(3):92-98
Ohne Zusammenfassung 相似文献