Mutation proximal to the tRNA binding region of the Nicotiana plastid 16S rRNA confers resistance to spectinomycin.

Summary Nicotiana tabacum lines carrying maternally inherited resistance to spectinomycin were obtained by selection for green callus in cultures bleached by spectinomycin. Two levels of resistance was found. SPC1 and SPC2 seedlings are resistant to high levels (500 g/ml), SPC23 seedlings are resistant to low levels (50 g/ml) of spectinomycin. Lines SPC2 and SPC23 are derivatives of the SR1 streptomycin-resistant plastome mutant. Spectinomycin resistance is due to mutations in the plastid 16S ribosomal RNA: SPC1, an A to C change at position 1138; SPC2, a C to U change at position 1139; SPC23, a G to A change at position 1333. Mutations similar to those in the SPC1 and SPC2 lines have been previously described, and disrupt a conserved 16S ribosomal RNA stem structure. The mutation in the SPC23 line is the first reported case of a mutation close to the region of the 16S rRNA involved in the formation of the initiation complex. The new mutants provide markers for selecting plastid transformants.     

PCR检测淋球菌的探讨

多聚酶链反应（ＰＣＲ）具有灵敏度高,特异性强,快速高效的特点,在病原微生物检测领域有广阔的前景。本文对４０８例疑似淋病患者的泌尿生殖道分泌物作了ＰＣＲ检测淋球菌的探索,结果１７０例阳性,占４１．７％,而培养阳性（２１．６％）,ＰＣＲ法显著高于培养法（Ｐ＜０．０１）。     

Plastid transformation in Arabidopsis thaliana

Plastid transformation is reported in Arabidopsis thaliana following biolistic delivery of transforming DNA into leaf cells. Transforming plasmid pGS31A carries a spectinomycin resistance (aadA) gene flanked by plastid DNA sequences to target its insertion between trnV and the rps12/7 operon. Integration of aadA by two homologous recombination events via the flanking ptDNA sequences and selective amplification of the transplastomes on spectinomycin medium yielded resistant cell lines and regenerated plants in which the plastid genome copies have been uniformly altered. The efficiency of plastid transformation was low: 2 in 201 bombarded leaf samples. None of the 98 plants regenerated from the two lines were fertile. Received: 13 February 1998 / Revision received: 24 April 1998 / Accepted: 5 June 1998     

淋球菌引起的急性盆腔腹膜炎的病例分析

本文对我院９１￣９４年收治的３５例，由淋球菌引起的急性淋菌性盆腔腹膜炎的发病情况进行了分析。资料显示：淋菌性盆腔腹膜炎发病以中青年妇女为多。性乱及不洁的性生活是诱发本病的原因。无先兆症状使本病无特异性，但脓性白带、尿路刺激症状、宫颈与阴道壁充血以及腹膜刺激症有助于本病的诊断。确诊则依据涂片染色检菌及细菌培养。大剂量的青霉素或第三代头孢菌素的应用，可使本病早日治愈。     

Spectinomycin operon ofMicrococcus luteus: Evolutionary implications of organization and novel codon usage

Summary The complete DNA sequence of theMicrococcus luteus spectinomycin (spc) operon and its adjacent regions has been determined. The sequence has revealed the presence of genes that are homologous to those of theEscherichia coli ribosomal and related proteins, L14, L24, L5, S8, L6, L18, S5, L30, L15, and secretion protein Y (secY), and the gene for adenylate kinase (adk). The gene arrangement in the spc operon is essentially the same as that ofE. coli except for the absence in theM. luteus spc operon of the genes for S14 and X protein that exist in theE. coli spc operon.SecY andadk seem to be composed of another operon (adk operon) with at least an open reading frame. The deduced amino acid sequences for these ribosomal proteins are well conserved among the two species (40–65% identity). Reflecting the high genomic guanine and cytosine (GC) content ofM. luteus (74%), the codon usage of the genes is extremely biased toward use of G and C, about 94% of the codon third positions being G or C. Seven codons, AUA, AAA, AGA, UUA, GUA, CUA, and CAA, all of which have A at the codon third positions, are completely absent in theM. luteus genes examined. Out of 11 genes in theM. luteus spc and adk operons, 5 (10) use GUG (UGA) and 6 (1) use AUG (UAA) as an initiation (termination) codon.     

Spontaneous spectinomycin resistance mutations detected after biolistic transformation of Daucus carota L.

Spectinomycin resistant mutant carrot (Daucus carota L.) callus lines detected in the experiments on biolistic transformation of plastome were analyzed. It has been found that this antibiotic resistance is determined by point nucleotide substitutions at two distinct sites of the chloroplast gene rrn16, coding for 16S rRNA, namely, G1012T, G1012C, and A1138G. The detected mutations are localized to the 16S rRNA region forming helix h34, which contains spectinomycin binding site, and lead to its destabilization by several kilocalories per mole. Comparative analysis of rrn16 gene sequences has demonstrated conservation of the positions of the nucleotide substitutions determining this antibiotic resistance in carrot (D. carota L.), tobacco (Nicotiana tabacum L.), and bladder pod (Lesquerella fendleri L.), as well as in Escherichia coli.     

Lactate carbon does not enter the sugars of lipopolysaccharide when gonococci are grown in a medium containing glucose and lactate: implications in vivo

In media containing glucose, lactate stimulates the metabolism of gonococci at concentrations that simulate conditions in vivo. Nuclear magnetic resonance (NMR) spectroscopy of (13)C-labelled lipids obtained from gonococci grown in a synthetic medium with (13)C-labelled lactate and unlabelled glucose (culture A), (13)C-labelled glucose alone (culture B) or (13)C-labelled glucose and unlabelled lactate (culture C) showed lactate carbon was not present in glycerol/ethanolamine residues of lipids from culture A. This indicated that, in the presence of glucose, lactate gluconeogenesis is shut down. Hence, the stimulation of metabolism could result from the production of extra energy because lactate is used solely for conversion to acetyl-CoA, the precursor of fatty acid synthesis and the components of the tricarboxylic acid cycle. In this paper, additional evidence for lack of gluconeogenesis has been sought using a different approach. The carbohydrate moieties of lipopolysaccharide (LPS) have been examined for lactate carbon after gonococci were grown with lactate and glucose. Two methods were used: NMR spectroscopy of (13)C-labelled lipopolysaccharide purified from the three cultures described above showed that, in the presence of glucose, lactate carbon, in contrast to glucose carbon, was not in the carbohydrate moiety. Also, (14)C-labelled lactate was added to a culture containing unlabelled glucose and lactate (culture A) and [(14)C]glucose to cultures containing unlabelled glucose without unlabelled lactate (culture B) and with unlabelled lactate (culture C). When LPS samples purified from these cultures were subjected to hydrazinolysis, the ratio of the radioactivity of water-soluble products (carbohydrate moieties) to those of chloroform-soluble products (fatty acids) was much lower when [(14)C]lactate was used in culture A, than when [(14)C]glucose was used in cultures B and C. Thus, in the presence of glucose, lactate carbon, unlike glucose carbon, is incorporated predominantly into fatty acids of LPS, not into its carbohydrate moieties. There is no doubt, therefore, that gluconeogenesis is shut off when lactate is present with glucose and there is a consequent stimulation of metabolism. This probably occurs in vivo on mucous surfaces, where gonococci are surrounded by a mixture of glucose and lactate in the secretions.     

Neisseria gonorrhoeae contains multiple copies of a gene that may encode a site-specific recombinase and is associated with DNA rearrangements

A 960-bp ORF potentially encoding a site-specific recombinase has been cloned from Neisseria gonorrhoeae MS11-A. This ORF was designated piv_Ng on the basis of similarity of the deduced amino acid sequence to the Piv proteins of Moraxella spp. that are site-specific invertases. Southern hybridization and sequence analysis revealed that there were multiple copies of piv_Ng sequence within the genomes of N. gonorrhoeae strains tested, but not in several other neisserial species. Southern hybridization and sequence analysis further suggested that piv_Ng sequences may be associated with genomic rearrangements.