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151.
152.
Haseltine C Hill T Montalvo-Rodriguez R Kemper SK Shand RF Blum P 《Journal of bacteriology》2001,183(1):287-291
Few antibiotics targeting members of the archaeal domain are currently available for genetic studies. Since bacterial antibiotics are frequently directed against competing and related organisms, archaea by analogy might produce effective antiarchaeal antibiotics. Peptide antibiotic (halocin) preparations from euryarchaeal halophilic strains S8a, GN101, and TuA4 were found to be toxic for members of the hyperthermophilic crenarchaeal genus Sulfolobus. No toxicity was evident against representative bacteria or eukarya. Halocin S8 (strain S8a) and halocin R1 (strain GN101) preparations were cytostatic, while halocin A4 (strain TuA4) preparations were cytocidal. Subsequent studies focused on the use of halocin A4 preparations and Sulfolobus solfataricus. Strain TuA4 cell lysates were not toxic for S. solfataricus, and protease (but not nuclease) treatment of the halocin A4 preparation inactivated toxicity, indicating that the A4 toxic factor must be a secreted protein. Potassium chloride supplementation of the Sulfolobus assay medium potentiated toxicity, implicating use of a salt-dependent mechanism. The utility of halocin A4 preparations for genetic manipulation of S. solfataricus was assessed through the isolation of UV-induced resistant mutants. The mutants exhibited stable phenotypes and were placed into distinct classes based on their levels of resistance. 相似文献
153.
154.
A rate-independent technique for analysis of nucleic acid sequences: evolutionary parsimony 总被引:24,自引:1,他引:23
The method of evolutionary parsimony--or operator invariants--is a
technique of nucleic acid sequence analysis related to parsimony analysis
and explicitly designed for determining evolutionary relationships among
four distantly related taxa. The method is independent of substitution
rates because it is derived from consideration of the group properties of
substitution operators rather than from an analysis of the probabilities of
substitution in branches of a tree. In both parsimony and evolutionary
parsimony, three patterns of nucleotide substitution are associated
one-to-one with the three topologically linked trees for four taxa. In
evolutionary parsimony, the three quantities are operator invariants. These
invariants are the remnants of substitutions that have occurred in the
interior branch of the tree and are analogous to the substitutions assigned
to the central branch by parsimony. The two invariants associated with the
incorrect trees must equal zero (statistically), whereas only the correct
tree can have a nonzero invariant. The chi 2-test is used to ascertain the
nonzero invariant and the statistically favored tree. Examples, obtained
using data calculated with evolutionary rates and branchings designed to
camouflage the true tree, show that the method accurately predicts the
tree, even when substitution rates differ greatly in neighboring peripheral
branches (conditions under which parsimony will consistently fail). As the
number of substitutions in peripheral branches becomes fewer, the parsimony
and the evolutionary-parsimony solutions converge. The method is robust and
easy to use.
相似文献
155.
156.
Carbamoylphosphate synthetase (CPS) catalyzes the first committed step in
pyrimidine biosynthesis, arginine biosynthesis, or the urea cycle.
Organisms may contain either one generalized or two specific CPS enzymes,
and these enzymes may be heterodimeric (encoded by linked or unlinked
genes), monomeric, or part of a multifunctional protein. In order to help
elucidate the evolution of CPS, we have performed a comprehensive
phylogenetic analysis using the 21 available complete CPS sequences,
including a sequence from Sulfolobus solfataricus P2 which we report in
this paper. This is the first report of a complete CPS gene sequence from
an archaeon, and sequence analysis suggests that it encodes an enzyme
similar to heterodimeric CPSII. We confirm that internal similarity within
the synthetase domain of CPS is the result of an ancient gene duplication
that preceded the divergence of the Bacteria, Archaea, and Eukarya, and use
this internal duplication in phylogenetic tree construction to root the
tree of life. Our analysis indicates with high confidence that this
archaeal sequence is more closely related to those of Eukarya than to those
of Bacteria. In addition to this ancient duplication which created the
synthetase domain, our phylogenetic analysis reveals a complex history of
further gene duplications, fusions, and other events which have played an
integral part in the evolution of CPS.
相似文献
157.
Plasma propranolol levels associated with reductions in endogenous and exogenous cardiac β-stimulation were determined in normal people. The levels associated with a given degree of blockade of exercise-induced tachycardia were about three times greater after intravenous administration than after oral administration. This shows that an active metabolite of propranolol is formed only after the drug is taken by mouth. The greatest reduction in the tachycardia of strenuous exercise was associated with plasma levels of 40 ng./ml. with oral administration and 100 ng./ml. with intravenously administered propranolol.The effect on isoprenaline-induced tachycardia following intravenously administered propranolol showed that the dose ratio for isoprenaline was about 30 with plasma levels of 100 ng./ml. and 10 with levels of 10-20 ng./ml. These plasma levels give 100% and 20-30% blockade of exercise-induced tachycardia. These findings suggest that some of the therapeutic effects of propranolol may be unrelated to β-adrenergic blockade. 相似文献
158.
Alves-Gomes JA; Orti G; Haygood M; Heiligenberg W; Meyer A 《Molecular biology and evolution》1995,12(2):298-318
The order Gymnotiformes (South American electric fishes) is a fascinating
assemblage of freshwater fishes that share the unusual ability to produce
and sense electric fields used for electrolocation and social
communication. In the last few decades, the electrogenic and electrosensory
systems (EES) of these fish have served as an excellent model to study
motor and sensory physiology in vertebrates. In an attempt to the evolution
of characters associated with the EES in the group, we applied
maximum-parsimony (MP), minimum-evolution (ME), and maximum-likelihood (ML)
methods to analyze 302 aligned bases of the mitochondrial 12S rRNA and 416
bases of the mitochondrial 16S rRNA of 19 gymnotiform genera representing
all six recognized families. Six catfish genera (order Siluriformes) were
also sequenced and used as outgroups. The phylogenetic hypothesis resultant
from molecular data analysis differs in some respects from previous
hypotheses based on morphological studies. Our results were most
informative within the family level, as we were unable to elucidate the
relationships among deeper branches in this order with sufficient
confidence by using molecular data alone. The phylogenetic information of
both mitochondrial DNA segments appears to be affected by functional
constraints, and the resultant topologies were sensitive to different
weighting schemes and the algorithm used. Nonetheless, we found unanimous
support for the following phylogenetic relationships: (1) the family
Sternopygidae is an unnatural group, and Sternopygus is the sole
representative of a unique lineage within the order; (2) the family
Hypopomidae is not monophyletic; and (3) the order Gymnotiformes is
composed of at least six natural clades: Sternopygus, family Apteronotidae,
a new clade consisting of the remaining sternopygids, families Hypopomidae
+ Rhamphicthyidae, family Electrophoridae, and family Gymnotidae. By
combining molecular, morphological, and physiological information, we
propose a new hypothesis for the phylogeny of this group and suggest a new
family Eigenmanniidae n. (order Gymnotiformes).
相似文献
159.
López-Valenzuela BE Armenta-Bojórquez AD Hernández-Verdugo S Apodaca- Sánchez MA Samaniego-Gaxiola JA Valdez-Ortiz A 《Phyton》2019,88(1):37-46
Microbes that are beneficial to plants are used to
enhance the crop growth, yield and are alternatives to chemical
fertilizers. Trichoderma and Bacillus are the predominant plant
growth-promoting fungi and bacteria. The objective of this study
was select, characterize, and evaluate isolates of Trichoderma
spp. and Bacillus spp. native from the northern region of Sinaloa,
Mexico, and assess their effect on growth promotion in maize (Zea
mays L.). In greenhouse conditions, four Trichoderma isolates and
twenty Bacillus isolates, as well as two controls, were tested in a
completely randomized design with three replicates. We selected
the two best strains of Trichoderma and Bacillus: TB = Trichoderma
asperellum, TF = Trichoderma virens, B14 = Bacillus cereus sensu
lato and B17 = Bacillus cereus, which were evaluated in the field in
a completely randomized blocks in factorial arrangement design
with three replicates applying different rates of nitrogen fertilizer
(0, 150 kg N/ha, and 300 kg N/ha). Treatments 5 (B17 = B. cereus)
and 11 (TF = T. virens) both fertilized with 150 kg N/ha showed
similar yields and they did not reveal significant differences from
the treatments fertilized with 300 kg N/ha. This indicated that
treatment 5 (B17= B. cereus with 150 kg N/ha) and treatment
11 (TF= T. virens with 150 kg N/ha) were efficient as growth
promoters, by not showing significant differences in root volume
and dry weight of foliage. The results indicated a reduction of 50%
in the rate of nitrogen to fertilizer required for maize (Zea mays
L.) crops. These microorganisms Trichoderma and Bacillus could
be an alternative to reduce the use of chemical fertilizers in maize. 相似文献
160.
Synthetic sheep urine additions (59 g N m−2) were made to pastures on two soils, at Fasset, a semi-natural grassland, and Strathfinella, an improved pasture. Urine was
applied to microplots in May and the soil, grass and soil solution analyzed 1, 2, 4, 5, 12 and 23 weeks after the addition.
At Fasset, the grass was scorched by urine and the standing biomass decreased compared to the control, increasing only after
5 weeks. The absence of scorching at the Strathfinella site was attributed to a greater biomass of root mat to buffer the
roots from exposure to NH3and a greater rainfall immediately following treatment. Scorching reduced the uptake of N and it was not clear if the greater
contents of NH4
+ and the increases in soil pH at Fasset compared with Strathfinella were the causes or symptoms of the scorch effect. Amounts
of extractable organic N (DON) were similar in both soils and increased during the first 4 weeks and then decreased. Urine
addition both increased and decreased DON at different times, but the overall mean values were unchanged. Urine application
changed the distribution of P in the two soils, increasing the soil solution P at Fasset by 80 mg P m−2 and raising the P content of herbage at Strathfinella by 600 mg P m−2. In the soil solution, dissolved forms of molybdate reactive P, organic P and condensed P fractions were all increased by
the urine addition. After 23 weeks, condensed P made the greatest contribution to soil solution P in both soils indicating
that this fraction was the least available for plant uptake.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献