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21.
Data collected from a longitudinal survey carried out over 2 years on four farms in western France were used to assess the incidence and infestation of Ixodes ricinus on rodents. Once a month, on each farm, 25 Sherman live traps were set in hedges bordering selected pastures. A total of 799 micromammals were examined, including Apodemus sylvaticus, Clethrionomys glareolus, Microtus agrestis, Microtus arvalis, and Crocidura spp. Larvae and nymphs of I. ricinus were found. Small numbers of Ixodes (Exopalpiger) trianguliceps were also recovered from each farm. The mean infestation rate of the I. ricinus larvae (1.6–5.9) among all animals examined varied between farms Most animals were infested by only a single tick, but one M. agrestis harboured 43 I. ricinus larvae. Larvae or nymphs were found throughout the year, with peaks from March to October.  相似文献   
22.
TOL plasmid pWW0 from Pseudomonas putida mt-2 encodes catabolic enzymes required for the oxidation of toluene and xylenes. The structural genes for these catabolic enzymes are clustered into two operons, the xylCMABN operon, which encodes a set of enzymes required for the transformation of toluene/xylenes to benzoate/toluates, and the xylXYZLTEGFJQKIH operon, which encodes a set of enzymes required for the transformation of benzoate/toluates to Krebs cycle intermediates. The latter operon can be divided physically and functionally into two parts, the xylXYZL cluster, which is involved in the transformation of benzoate/toluates to (methyl)catechols, and the xylTEGFJQKIH cluster, which is involved in the transformation of (methyl)catechols to Krebs cycle intermediates. Genes isofunctional to xylXYZL are present in Acinetobacter calcoaceticus, and constitute a benzoate-degradative pathway, while xylTEGFJQKIH homologous encoding enzymes of a methylphenol-degradative pathway and a naphthalene-degradative pathway are present on plasmid pVI150 from P. putida CF600, and on plasmid NAH7 from P. putida PpG7, respectively. Comparison of the nucleotide sequences of the xylXYZLTEGFJQKIH genes with other isofunctional genes suggested that the xylTEGFJQKIH genes on the TOL plasmid diverged from these homologues 20 to 50 million years ago, while the xylXYZL genes diverged from the A. calcoaceticus homologues 100 to 200 million years ago. In codons where amino acids are not conserved, the substitution rate in the third base was higher than that in synonymous codons. This result was interpreted as indicating that both single and multiple nucleotide substitutions contributed to the amino acid-substituting mutations, and hence to enzyme evolution. This observation seems to be general because mammalian globin genes exhibit the same tendency.  相似文献   
23.
Summary— We have previously shown the presence, in the amplified DNA of a Drosophila cell line resistant to N-phosphonacetyl-L-aspartate (PALA), of two units of 150 kb and 120 kb respectively duplicated and amplified. The two joints (J1 and J2) linking these units as well as their respective wild-type counterparts have been sequenced. Sequence analysis indicates that a region of the Drosophila genome which corresponds to the proximal boundary of the 150 kb unit is common to both joints. In addition to this common region, the J1 junction possesses a 26-nucleotide sequence belonging to the J2 junction. This indicates that the J2 junction was the first formed, and that J1, therefore, results from recombination between J2 and a region of the wild-type genome 120 kb distal to J2. Sequence analysis also reveals that the joints result from illegitimate recombination between unrelated regions. AT-rich sequences, strand bias composition and putative topoisomerase I and II sites were found in at least one of the two parental sequences involved in the formation of the joints. On the basis of these results we can hypothesize that after two illegitimate recombinations between sister chromatids, leading first to J2 and then to J1, the amplification may have arisen by a series of homologous (unequal crossing-over) or illegitimate recombinations, or by an intrachromosomal rolling circle.  相似文献   
24.
We have used fluorescence in situ hybridization to map the positions of the different repetitive DNA sequences from the region forming the lampbrush loop pair Nooses on the Y chromosome of Drosophila hydei. This region harbours a megabase cluster of tandemly organized repeats of the Y-specific ay1 family and a megabase cluster of tandem repeats of the related Y-specific YsI family. In addition, ay1 repeats also occur in short blocks that are interspersed by other repetitive DNA sequences that we call Y-associated, since they have additional copies on other chromosomes. Using specific probes for ay1, YsI and Y-associated DNA sequences, we show that there is one large proximal cluster of YsI repeats and one, more distally located, large cluster of ay1 repeats. The Y-chromosomal copies of the Y-associated sequences are located in the most distal part of the ay1 cluster. This is consistent with the juxtaposition of ay1 and Y-associated sequences in more than 300 kb of cloned genomic DNA. Since both ay1 and Y-associated sequences have been shown to be transcribed in the Nooses, the lampbrush loop is formed in a distal region of the short arm of the Y chromosome, adjacent to the terminally located nucleolus organizer region. The clusters of homogeneous ay1 and YsI repeats are of no functional significance for the formation of the lampbrush loop.  相似文献   
25.
Iron content of sediment and phosphate adsorption properties   总被引:9,自引:2,他引:7  
Phosphorus can occur in sediments in different forms and accordingly its availability varies. The distinction between the phosphorus fractions is made with two chemical extraction methods; an ammonium oxalate-oxalic acid extraction and an extraction according to Hieltjes & Lijklema (1980).The iron and aluminum liberated with the ammonium oxalate-oxalic acid extraction method is linearly correlated (r 2 = 0.73) with the phosphorus liberated in the first two steps of the Hieltjes and Lijklema extraction by: P = 0.035 (Fe + Al) + 0.001 (P, Fe and Al in mmol g–1).The iron and aluminum (hydr)oxides are very important fractions in the sediment adsorption capacity for phosphorus. The phosphorus sorption capacity (PSC) is 0.080 mol P (mol (Fe + Al))–1 and the adsorption constant (k) is 11.9 µmol P l–1. Here it is assumed that iron and aluminum (hydr)oxide have the same affinity for phosphorus.  相似文献   
26.
We have recently cloned three DNA fragments (In-2.6, In-1.0, and In-0.6) of the noncultured, bacterial-like organism (BLO) associated with citrus greening disease. Nucleotide sequence determination has shown that fragment In-2.6 is part of therplKAJL-rpoBC gene cluster, a well-known operon in eubacteria. The DNA fragment upstream of and partially overlapping with In-2.6 could be isolated and was shown to be thenusG gene. InEscherichia coli, nusG is also immediately upstream ofrplKAJL-rpoBC. Fragment In-1.0 carries the gene for a bacteriophage type DNA polymerase. Fragment In-0.6 could not be identified.When In-2.6 was used, at high stringency, as a probe to detect greening BLO strains in infected plants, hybridization was obtained with all Asian strains tested, but not with the African strain examined. At lower stringencies, In-2.6 was able to detect also the African strain. The implications of these reults in the taxonomical position of the greening BLO are discussed.  相似文献   
27.
The symbioses between plants of the Rubiaceae and Primulaceae families with Burkholderia bacteria represent unique and intimate plant–bacterial relationships. Many of these interactions have been identified through PCR-dependent typing methods, but there is little information available about their functional and ecological roles. We assembled 17 new endophyte genomes representing endophytes from 13 plant species, including those of two previously unknown associations. Genomes of leaf endophytes belonging to Burkholderia s.l. show extensive signs of genome reduction, albeit to varying degrees. Except for one endophyte, none of the bacterial symbionts could be isolated on standard microbiological media. Despite their taxonomic diversity, all endophyte genomes contained gene clusters linked to the production of specialized metabolites, including genes linked to cyclitol sugar analog metabolism and in one instance non-ribosomal peptide synthesis. These genes and gene clusters are unique within Burkholderia s.l. and are likely horizontally acquired. We propose that the acquisition of secondary metabolite gene clusters through horizontal gene transfer is a prerequisite for the evolution of a stable association between these endophytes and their hosts.  相似文献   
28.
Summary N6-benzyl-adenine (BA) enhanced phyllogenesis and axillary bud development of Paeonia suffruticosa during in vitro culture allowing good propagation while N6-(2isopentenyl)adenine (iP) did not. During the first five days of culture, the mitotic activity of BA-treated explants was higher than in the iP-treated ones. High BA levels were detected in the BA-treated explants, and this was correlated with the absence of or the low indole-3-acetic acid (IAA) content. The low iP levels measured in iP-treated explants were correlated with high endogenous IAA content; the new cytokinin / auxin ratio could explain the lack of axillary buds and the development of only one leaf. Abscisic acid (ABA) was detected neither in the controls nor in the cytokinin-treated explants during the first week. However, intensive restoration of ABA accumulation was observed in controls from the third week onwards. Both BA and iP-treated explants accumulated less ABA than the controls but this hormone appeared later in the BA-treated explants than in the iP-treated ones.Abbreviations ABA abscisic acid - BA N6-benzyl-adenine - BHT butyl-hydroxy-toluene - ELISA enzyme linked immunosorbent assay - FM fresh mass - HPLC high performance liquid chromatography - IAA indole-3-acetic acid - iP N6-(2-isopentenyl)adenine - MI mitotic index - 9RBA 9-ß-D-ribofuranosyl-BA - 9RiP 9-ß-Dribofuranosyl-iP - 9RZ 9-ß-D-ribofuranosyl-zeatin - Z zeatin  相似文献   
29.
Through use of commercially available DnaK proteins and anti-DnaK monoclonal antibodies, a competitive enzyme-linked immunosorbent assay was developed to quantify this heat shock protein in Escherichia coli ATCC 25922 subjected to various heating regimens. For a given process lethality (F7010 of 1, 3, and 5 min), the intracellular concentration of DnaK in E. coli varied with the heating temperature (50 or 55°C). In fact, the highest DnaK concentrations were found after treatments at the lower temperature (50°C) applied for a longer time. Residual DnaK after heating was found to be necessary for cell recovery, and additional DnaK was produced during the recovery process. Overall, higher intracellular concentrations of DnaK tended to enhance cell resistance to a subsequent lethal stress. Indeed, E. coli cells that had undergone a sublethal heat shock (105 min at 55°C, F7010 = 3 min) accompanied by a 12-h recovery (containing 76,786 ± 25,230 molecules/cell) resisted better than exponentially growing cells (38,500 ± 6,056 molecules/cell) when later heated to 60°C for 50 min (F7010 = 5 min). Results reported here suggest that using stress protein to determine cell adaptation and survival, rather than cell counts alone, may lead to more efficient heat treatment.  相似文献   
30.
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