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1.
Attached bacterial populations cultured without an exogenous carbon source or grown in conjunction with attached diatoms incorporated [3H]thymidine at a rate between four and five times lower than that of replicate bacterial populations which were dispersed before being assayed. 相似文献
2.
Nitrogen dynamics in two antarctic streams 总被引:1,自引:1,他引:0
The many glacier meltwater streams of southern Victoria Land flow through catchments where life forms are almost entirely microbial. Allochthonous inputs of nitrogen from two study streams near McMurdo Sound were derived mostly from the melting glaciers (ca. 100–200 mg N m–3) with some originating from N2-fixation by heterocystous cyanobacteria (max. 939 mg N m–2 year–1). Thirty to fifty per cent of the glacier derived N was dissolved organic N and a major proportion of this was identified as urea N which was utilised by the rich algal and cyanobacterial mats in the streams. A nutrient budget for Fryxell Stream was estimated, quantifying uptake of urea-N and dissolved inorganic N and the release of dissolved organic (non urea) and particulate N by the stream communities. An index of in-stream nitrogen processing, the Net Uptake Length Constant in these streams was compared with that from temperate climates and was found to be similar. Despite the influence of low temperatures on microbial activity (mean daily water temperature = 5 °C) nutrient removal rates from these antarctic streams are high because of the large standing stock of microbial biomass there. 相似文献
3.
Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes 总被引:23,自引:2,他引:21
Statistical methods for computing the standard errors of the branching
points of an evolutionary tree are developed. These methods are for the
unweighted pair-group method-determined (UPGMA) trees reconstructed from
molecular data such as amino acid sequences, nucleotide sequences,
restriction-sites data, and electrophoretic distances. They were applied to
data for the human, chimpanzee, gorilla, orangutan, and gibbon species.
Among the four different sets of data used, DNA sequences for an
895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the
most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979)
gave the least reliable one. The DNA sequence data suggested that the
chimpanzee is the closest and that the gorilla is the next closest to the
human species. The orangutan and gibbon are more distantly related to man
than is the gorilla. This topology of the tree is in agreement with that
for the tree obtained from chromosomal studies and DNA-hybridization
experiments. However, the difference between the branching point for the
human and the chimpanzee species and that for the gorilla species and the
human-chimpanzee group is not statistically significant. In addition to
this analysis, various factors that affect the accuracy of an estimated
tree are discussed.
相似文献
4.
Temperature dependence of inorganic nitrogen uptake and assimilation in Antarctic sea-ice microalgae 总被引:3,自引:0,他引:3
John C. Priscu Anna C. Palmisano Linda R. Priscu Cornelius W. Sullivan 《Polar Biology》1989,9(7):443-446
Summary The influence of temperature on NO
3
-
and NH
4
+
uptake, and the activity of the assimilatory enzyme NO
3
-
reductase (NR) was compared to inorganic C uptake (photosynthesis) in natural assemblages of Antarctic sea-ice microalgae. NO
3
-
and NH
4
+
uptake reached a maximum between 0.5°–2.0°C and 2.0°–3.0°C, respectively, which was close to that for photosynthesis (2.5°–3.0°C). NR showed a distinctly higher temperature maximum (10.0°–12.0°C) and a lower Q10 value than inorganic N and C transport. Our data imply that, owing to differential temperature characteristics between N transport and N assimilation at in situ temperature (-1.9°C), the incorporation of extracellular NO
3
-
into cellular macromolecules, may be limited by transport of NO
3
-
into the cell rather than the intracellular reduction of NO
3
-
to NH
4
+
. Despite differences in temperature maxima between N transport and N assimilation, the overall low temperature maxima of inorganic N metabolism characterizes Antarctic sea-ice microalgae as psychrophilic. Our study is the first to examine the temperature dependence of inorganic N uptake and assimilation in sea-ice microbial communities. 相似文献
5.
6.
7.
Detection and characterization of denitrifying bacteria from a permanently ice-covered Antarctic Lake 总被引:2,自引:0,他引:2
Denitrifying bacterial strains were isolated from Lake Bonney,apermanently ice-covered and chemically stratified lake in theMcMurdo dry valley region of Antarctica, using complex mediaat4 °C. Three strains, identified as denitrifiers bytheirability to produce nitrous oxide using nitrate or nitrite as arespiratory substrate, were characterized as to theirtemperatureand salinity optima for aerobic growth in batch culture; allthreewere psychrophilic and moderately halophilic. Maximum growthratesof near 0.024 h–1 were measured for all three strains.Growthrates projected to occur at in situ temperature andsalinityimply generation times on the order of 100 h. Species specificpolyclonal antisera were prepared against two of the strains,ELB17 (from the east lobe of the lake at 17 m) and WLB20 (fromthewest lobe at 20 m). Both strains were subsequently detectedandenumerated in the lake using the antisera. ELB17 was presentinboth lobes below the chemocline, while WLB20 was present inthewest lobe below the chemocline but only in surface waters oftheeast lobe. These distributions are related to the observedchemicaldistributions which imply the occurrence of denitrification inthewest lobe of the lake and not in the east lobe. 相似文献
8.
Identification of the signalling molecules involved in mesoderm formation in amphibian embryos still presents problems. None of the original candidates, such as activin, have been definitively ruled out, and the new factors, such as the nodal-related genes, have come on to the scene. Of the original candidates, activin has been definitively shown to act as a morphogen, whereas bone morphogenetic protein (BMP)-4 has emerged as a ventral inducer and an inhibitor of neural differentiation. The effects of BMP-4 are antagonized by chordin, a molecule related to the product of the Drosophila gene short gastrulation. 相似文献
9.
Rates of , and CO2 assimilationby the organisms in the shallow and deepchlorophyll layers ofCastle Lake were measured over a gradient of photosyntheticphoton flux densities (PPFD) during the 19791980 ice-freeseasons. The results of these experiments could be fitted witha hyperbolic function in the manner of the Michaelis-Mentenequation (excluding rates of dark assimilation) up to 40%of the surface PPFD after which photon inhibition occurred.The half saturation constants relative to incidence PPFD (KLT)for assimilation ( = 1.1 E m2d2) were about twice those for ( = 0.5 E m2d1).All of the KLT values correspond to depths in thelakerangingfrom 1729 m(1% of surface PPFD). Dark assimilationof both and was 50% of the assimilation at saturating PPFD implying that part ofthe immediate energy required for inorganic nitrogen assimilationmay come from intermediary metabolism. This contention was supportedfor assimilation by the results of experiments performed with specific inhibitors of non-cyclic photophosphorylationand oxidative phosphorylation. The KLT values for the assimilationof CO2 were from 210 times higher than those for inorganicnitrogen. These values for CO2 assimilation were not significantlyaltered by the addition of either or during 12 h incubations. 相似文献
10.