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Biosynthesis of a 42-kD Polypeptide in the Cytoplasmic Membrane of the Cyanobacterium Anacystis nidulans Strain R2 during Adaptation to Low CO(2) Concentration.

When cells of Anacystis nidulans strain R2 grown under high CO(2) conditions (3%) were transferred to low CO(2) conditions (0.05%), their ability to accumulate inorganic carbon (C(i)) increased up to 8 times. Cytoplasmic membranes (plasmalemma) isolated at various stages of low CO(2) adaptation were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. There was a marked increase of a 42-kilodalton polypeptide in the cytoplasmic membrane during adaptation; a linear relationship existed between the amount of this polypeptide and the C(i)-accumulating capability of the cells. No significant changes were observed during this process in the amount of other polypeptides in the cytoplasmic membranes or in the polypeptide profiles of the thylakoid membranes, cell walls, and soluble fractions. Spectinomycin, an inhibitor of protein biosynthesis, inhibited both the increase of the 42-kilodalton polypeptide and the induction of high C(i)-accumulating capability. The incorporation of [(35)S]sulfate into membrane proteins was greatly reduced during low CO(2) adaptation. Radioautograms of the (35)S-labeled membrane proteins revealed that synthesis of the 42-kilodalton polypeptide in the cytoplasmic membrane was specifically activated during the adaptation, while that of most other proteins was greatly suppressed. These results suggested that the 42-kilodalton polypeptide in the cytoplasmic membrane is involved in the active C(i) transport by A. nidulans strain R2 and its synthesis under low CO(2) conditions leads to high C(i)-transporting activity.

Journal Article↗

Role of Protein Synthesis in Regulation of Phycobiliprotein mRNA Abundance by Light Quality in Fremyella diplosiphon.

If green light-acclimated Fremyella diplosiphon cultures are transferred to red light, the transcription from the inducible phycocyanin gene set increases at least 30-fold within 60 minutes. This effect is inhibited completely by the protein synthesis inhibitors chloramphenicol and spectinomycin. Application of chloramphenicol 30 minutes after transfer of cultures to inductive red light prevents further phycocyanin mRNA accumulation within 10 minutes. If red light-acclimated cells are transferred to green light, the phycocyanin transcript level declines by about 70% within 1 hour. Most of the green light-dependent decline results from the rapid cessation of transcription from the PC gene set. Chloramphenicol slows the decline to some extent by decreasing the rate of mRNA degradation in a light-independent manner. The accumulation of phycoerythrin mRNA after transfer of red light-acclimated cells to green light is also inhibited by chloramphenicol. However, there is no red light-dependent mechanism that rapidly halts phycoerythin mRNA synthesis after transfer of cultures from green to red light. Therefore, at least three light-dependent processes are involved in regulating phycobiliproteingene expression: chloramphenicol-sensitive processes required for the activation of phycocyanin and phycoerythrin gene sets and a chloramphenicol-insensitive process which blocks phycocyanin mRNA synthesis after transfer of cells from red to green light.

Journal Article↗

Chloroplast-encoded chlB is required for light-independent protochlorophyllide reductase activity in Chlamydomonas reinhardtii.

A chloroplast-encoded gene, designated chlB, has been isolated from Chlamydomonas reinhardtii, its nucleotide sequence determined, and its role in the light-independent reduction of protochlorophyllide to chlorophyllide demonstrated by gene disruption experiments. The C. reinhardtii chlB gene is similar to open reading frame 563 (orf563) of C. moewusii, and its encoded protein is a homolog of the Rhodobacter capsulatus bchB gene product that encodes one of the polypeptide components of bacterial light-independent protochlorophyllide reduction. To determine whether the chlB gene product has a similar role in light-independent protochlorophyllide reduction in this alga, a series of plasmids were constructed in which the aadA gene conferring spectinomycin resistance was inserted at three different sites within the chlB gene. The mutated chlB genes were introduced into the Chlamydomonas chloroplast genome using particle gun-mediated transformation, and homoplasmic transformants containing the disrupted chlB genes were selected on the basis of conversion to antibiotic resistance. Individual transformed strains containing chlB disruptions were grown in the dark or light, and 17 of the 18 strains examined were found to have a "yellow-in-the-dark" phenotype and to accumulate the chlorophyll biosynthetic precursor protochlorophyllide. RNA gel blot analysis of chlB gene expression in wild-type cells indicated that the gene was transcribed at low levels in both dark- and light-grown cells. The results of these studies support the involvement of the chlB gene product in light-independent protochlorophyllide reduction, and they demonstrate that, similar to its eubacterial predecessors, this green alga requires at least three components (i.e., chlN, chlL, and chlB) for light-independent protochlorophyllide reduction.

Amino Acid Sequence↗

A nuclear-encoded function essential for translation of the chloroplast psaB mRNA in chlamydomonas.

We report the analysis of a photosystem I-deficient mutant of Chlamydomonas reinhardtii, F15, that contains a mutation at the TAB1 (for translation of psaB mRNA) nuclear locus. Pulse labeling of chloroplast proteins revealed that the synthesis of the two photosystem I reaction center polypeptides PSAA and PSAB was undetectable in this mutant. The mRNA levels of these proteins were only moderately reduced, suggesting that the primary defect occurs at a step during or after translation. We constructed chimeric genes consisting of the psaA and psaB 5' untranslated region (5' UTR) fused to the aminoglycoside adenyltransferase (aadA) coding sequence, which confers spectinomycin resistance. Insertion of these genes into the chloroplast genome through biolistic transformation and analysis of their expression in the TAB1 mutant nuclear background revealed that the psaB (but not the psaA) 5' UTR is the target of the wild-type TAB1 function. This suggests that TAB1 is required for the initiation of psaB mRNA translation. The dependence of PSAA synthesis or accumulation on PSAB synthesis is strongly suggested by the identification of a suppressor mutation within the psaB 5' UTR. The suppressor specifically restores the synthesis of both proteins in the presence of the tab1-F15 mutation. The location of the suppressor mutation within a putative base-paired region near the psaB initiation codon suggests a role for TAB1 in the activation of translation of the psaB mRNA.

Amino Acid Sequence↗

Drug resistance and R plasmids in Bordetella bronchiseptica isolates from pigs.

A total of 207 strains of Bordetella bronchiseptica isolated from pigs in 1978 and 1979 were tested for drug resistance and for the properties of their R plasmids. Apart from intrinsic resistance to spectinomycin, single (sulfadimethoxine), double (sulfadimethoxine and streptomycin), andt riple (sulfadimethoxine, streptomycin, and ampicillin) resistance were found in 54.1%, 1.0%, and 15.9% of the strains, respectively. All of the triple-resistance determinants were associated with mercury resistance and were conjugative. pBB1, one of these R plasmids, was identified as Fi- (F) and Spp- (no suppression of phage multiplication) type, and as a member of incompatability group IncP. The single- and double-resistance determinants were nonconjugative. pBB2, one of the double-resistance determinants, was mobilized by an R plasmid, RP4, with the high efficiency of 80% and at a frequency of 3.3% without cotransfer of RP4. The molecular weight of pBB1 and pBB2 was estimated at 36 X 10(6) and 13 X 10(6) daltons, respectively, by electron microscopy and agarose gel electrophoresis. pBB1 had five cleavage sites for EcoRI endonuclease, and four sites for HindIII. pBB2 had two EcoRI sites, one HindIII, and one BamHI site. Cells carrying pBB1 or pBB2 produced enzymic activity tha inactivated streptomycin in the presence of ATP.

Animals↗

Prospective surveillance of community-onset and healthcare-associated methicillin-resistant Staphylococcus aureus isolated from a university-affiliated hospital in Japan.

We conducted a prospective comparative study of community-onset (CO) and healthcare-associated (HA) methicillin-resistant Staphylococcus aureus(MRSA) strains between 2000 and 2001 at Tokyo Women's Medical University Hospital (1,500 beds) in Japan. Of the 172 consecutive MRSA isolates analyzed, 13 (8%) were categorized as CO-MRSA. The mean age of patients with CO-MRSA was significantly younger than that of patients with HA-MRSA. Most CO-MRSA strains were isolated from skin and more likely to be susceptible to erythromycin, clindamycin, tetracycline, levofloxacin, and spectinomycin compared to HA-MRSA isolates. Pulsed-field gel electrophoresis (PFGE) analysis, staphylococcal cassette chromosome mec(SCCmec) typing, and multi-locus sequence typing (MLST) revealed that CO-MRSA strains were divided into the following multi-clones: 3 clone A: II: ST5 (PFGE type: SCCmec type: MLST sequence type); 1 L: II: ST5; 1 H: IV: ST1; 1 I: IV: ST81; 2 D: IV: ST8; 1 B: IV: ST89; 1 B: IV: ST379; and 3 B: IV: ST91. Of the 159 HAMRSA strains, 124 (78%) belonged to a single clone (PFGE clone A: SCCmec type II: tst and sec positive: coagulase type II: multi-drug resistance). Four CO-MRSA strains belonging to PFGE clone B: SCCmec type IV: MLST clonal complex 509 (ST89, 91, 379) had the exfoliative toxin B (etb) genes, but all CO-MRSA and HA-MRSA strains did not possess the Panton-Valentine leukocidin (pvl) genes. These results demonstrate that multiple lineages of CO-MRSA have the potential for dissemination in the community in Japan.

Adolescent↗

A new rapid and sensitive bioluminescence assay for antibiotics that inhibit protein synthesis.

A new sensitive, rapid and simple bioluminescence assay for antibiotics inhibiting protein synthesis is described. In this assay the ability of the tested antibiotic to inhibit the de novo synthesis of the enzymes participating in the bacterial luminescence system is determined by means of a dark variant of a luminous bacterium that undergoes prompt induction of the luminescence system with certain DNA-intercalating agents. Upon induction, the in vivo luminescence of the dark variant is increased more than 50-fold within 30 min. Antibiotics that block the de novo synthesis of protein limit the development of luminescence at a level that was found to be a function of the antibiotic concentration. The minimum detectable concentration of antibiotics in the bioluminescence test, after 45-60 min of incubation, was 0.1 microgram/ml for streptomycin, gentamicin, kanamycin, lincomycin and chloramphenicol and 0.3 microgram/ml for neomycin, clindamycin and spectinomycin. The new bioluminescence test has been used to assay these antibiotics in serum.

Anti-Bacterial Agents↗

Clinical pharmacology of tiamulin in ruminants.

Median values for the minimum inhibitory concentrations (MIC) of tiamulin for Mycoplasma and Acholeplasma isolated from ruminants were 0.05 micrograms/ml and 0.025 micrograms/ml, respectively. These values were close to the MIC values of tylosin and considerably lower than the respective values for spectinomycin, Spiramycin and oxytetracycline. The serum concentration--time profile of tiamulin after intramuscular (i.m.) injection to goats, ewes, cows and calves, and after oral administration to preruminant calves was characterized by a rapid absorption phase (absorption t1/2 of less than 30 min.), a short plateau phase, an elimination t1/2 ranging between 3 and 6 h, and low peak serum drug levels. The serum elimination t1/2 of the drug after intravenous (i.v.) injection was 25 min. It appears that tiamulin is extensively metabolized in ruminants and is well distributed throughout the body. Drug concentrations in the lungs, liver, and the kidneys 1 h after i.v. injection were four to seven times higher than in blood. The drug penetrated very rapidly into the milk after i.m. administration; mean peak drug concentrations in normal milk and in milk secreted from inflamed glands of cows were 7.5 times and 1.2 times higher respectively, than the mean peak serum drug concentrations. Concentrations of tiamulin of potential therapeutic value in the treatment of mycoplasmal infections can be maintained in the lungs for at least 12 h after i.m. injection at 10 mg/kg, and in preruminant calves after an oral dose of 20 mg/kg. However, tiamulin possesses several very serious side-effects and the i.v. route of administration is definitely contraindicated.

Administration, Oral↗

Transfer of plastid DNA from tobacco to the soil bacterium Acinetobacter sp. by natural transformation.

Acquisition of new genetic information by horizontal gene transfer is a major mechanism of genetic adaptation and evolution in prokaryotes. Naturally transformable cells of Acinetobacter sp. were exposed to plant DNA from leaf and root tissue of transplastomic tobacco. With the aadA gene (resistance against spectinomycin and streptomycin) as anchor sequence, the transfer of segments of the tobacco plastid DNA to Acinetobacter by homology-facilitated illegitimate recombination occurred at a frequency of 1.2 x 10(-7) per cell, which was about 0.1% of the frequency of fully homologous transfers. Without anchor sequence, transfer was not detected (</=1.3 x 10(-10)). The integrated plastid DNA segments extended up to 2539 nucleotides and often encompassed tobacco genes (trnL, ycf5). Expression of trnL (leucyl-tRNA) in a transformant was shown by reverse transcription polymerase chain reaction. About 44% of integration events occurred at a single hot-spot and 38% at other multiply used sites. All illegitimate recombination sites were GC-rich microhomologies of 3-6 bp often neighboured by further microhomologies. The sites were located in plant DNA at the ends of distinct larger high-GC regions, which suggests a role for GC-aided association of heterologous sequences in illegitimate DNA end joining. The results show that integration of plant DNA into a bacterial genome by natural transformation is possible and is probably stimulated by hot-spots of illegitimate recombination.

Acinetobacter↗

A novel approach to plastid transformation utilizes the phiC31 phage integrase.

Thus far plastid transformation in higher plants has been based on incorporation of foreign DNA in the plastid genome by the plastid's homologous recombination machinery. We report here an alternative approach that relies on integration of foreign DNA by the phiC31 phage site-specific integrase (INT) mediating recombination between bacterial and phage attachment sites (attB and attP, respectively). Plastid transformation by the new approach depends on the availability of a recipient line in which an attB site has been incorporated in the plastid genome by homologous recombination. Plastid transformation involves insertion of an attP vector into the attB site by INT and selection of transplastomic clones by selection for antibiotic resistance carried in the attP plastid vector. INT function was provided by either expression from a nuclear gene, which encoded a plastid-targeted INT, or expressing INT transiently from a non-integrating plasmid in plastids. Transformation was successful with both approaches using attP vectors with kanamycin resistance or spectinomycin resistance as the selective marker. Transformation efficiency in some of the stable nuclear INT lines was as high as 17 independently transformed lines per bombarded sample. As this system does not rely on the plastid's homologous recombination machinery, we expect that INT-based vectors will make plastid transformation a routine in species in which homologous recombination rarely yields transplastomic clones.

Attachment Sites, Microbiological↗

Plastid marker-gene excision by transiently expressed CRE recombinase.

We report plastid marker-gene excision with a transiently expressed CRE, site-specific recombinase. This is a novel protocol that enables rapid removal of marker genes from the approximately 10,000 plastid genome copies without transformation of the plant nucleus. Plastid marker excision was tested in tobacco plants transformed with a prototype polycistronic plastid vector, pPRV110L, designed to express multiple genes organized in an operon. The pMHB10 and pMHB11 constructs described here are dicistronic and encode genes for herbicide (bar) and spectinomycin (aadA) resistance. In vector pMHB11, expression of herbicide resistance is dependent on conversion of an ACG codon to an AUG translation initiation codon by mRNA editing, a safety feature that prevents translation of the mRNA in prokaryotes and in the plant nucleus. In the vectors, the marker gene (aadA) is flanked by 34-bp loxP sites for excision by CRE. Marker excision by a transiently expressed CRE involves introduction of CRE in transplastomic leaves by agro-infiltration, followed by plant regeneration. In tobacco transformed with vectors pMHB10 and pMHB11, Southern analysis and PCR identified approximately 10% of the regenerated plants as marker-free.

Biotechnology↗

Paromomycin and dihydrostreptomycin binding to Escherichia coli ribosomes.

Paromomycin binds specifically to a single type of binding site on the 70-S streptomycin-sensitive Escherichia coli ribosome. This site is different from that of dihydrostreptomycin since paromomycin binds to streptomycin-resistant ribosomes and sine dihydrostreptomycin does not compete for paromomycin binding. Paromomycin binding, unlike dihydrostreptomycin binding, is independent of changes in ribosome concentration but influenced by magnesium ion concentration. Moreover, paromomycin does not bind to the 30-S subunit of the streptomycin-sensitive ribosome, except in the presence of dihydrostreptomycin, which probably induces the conformational changes necessary for a paromomycin binding site. This induction does not occur with streptomycin-resistant ribosomes. Neither antibiotic binds to the 50-S subunit. In general, binding of the one antibiotic increases the number of sites available for binding of the other. Both antibiotics exhibit marked non-specific binding at high antibiotic/ribosome ratios. Competition studies have enabled the classification of other aminoglycosides according to their ability to compete for the paromomycin and dihydrostreptomycin binding sites. Derivatives structurally related to paromomycin compete for its binding, the degree of competition being related to antibacterial activity, but do not compete for dihydrostreptomycin binding; they, on the contrary, increase the number of dihydrostreptomycin binding sites. Neither gentamicin nor kanamycin derivatives, which induce a high level of misreading, nor kasugamycin and spectinomycin, which do not induce misreading, compete for paromomycin or dihydrostreptomycin binding sites. Other sites may be involved in the binding of these aminoglycosides and in inducing misreading.

Aminoglycosides↗

Polyamine requirement for streptomycin action on protein synthesis in bacteria.

The effect of streptomycin on polypeptide synthesis in vivo and in vitro has been investigated using polyamine auxotrophic mutants of Escherichia coli grown in the presence or in the absence of putrescine. We found that streptomycin caused a marked inhibition of protein synthesis in polyamine-supplemented cells whereas bacteria starved for polyamines were less sensitive to the action of the antibiotic. Neomycin, kanamycin and kasugamycin had a behaviour similar to streptomycin while spectinomycin, gentamicin and tetracycline brought about a strong inhibition of protein synthesis both in polyamine-starved and unstarved bacteria. The increase of misreading induced by the addition of streptomycin in vivo was higher in extracts derived from bacteria cultivated in the presence of polyamines. This effect was observed in cell-free systems of streptomycin-sensitive and resistant strains. In contrast, spermidine added in vitro caused an improvement in the accuracy of translocation. Analysis of sodium dodecyl sulphate/polyacrylamide gel electrophoresis of the labelled polypeptides synthesized in vivo seems to indicate that the starvation for polyamine or the presence of streptomycin may lead to premature termination with the appearance of unfinished peptide chains.

Aminoglycosides↗

Identification of an aadA2 gene cassette from Salmonella enterica subsp. enterica Serovar derby.

During a study on Salmonella enterica subsp. enterica serovar Derby from slaughter-age pigs in Brazil, two epidemiologically unrelated multi-resistant S. Derby isolates were found to carry a class 1 integron with a single gene cassette. Sequence analysis confirmed that this gene cassette harboured an aadA2 gene. The aadA2 gene codes for an aminoglycoside adenyltransferase, which mediates resistance to the aminoglycoside streptomycin and the aminocyclitol spectinomycin. Although aadA2 gene cassettes are widely distributed among Salmonella, database searches identified an AadA2 protein indistinguishable from that of S. Derby only in single isolates of S. enterica subsp. enterica Enteritidis from France and S. enterica subsp. enterica Typhimurium from Japan. Structural analysis of the 59-base element revealed at least one base pair difference between the 59-base element of the aadA2 cassette from S. Derby and any of the 59-base elements deposited in the databases.

Abattoirs↗

Increased zinc content in transplastomic tobacco plants expressing a polyhistidine-tagged Rubisco large subunit.

Rubisco is a hexadecameric enzyme composed of two subunits: a small subunit (SSU) encoded by a nuclear gene (rbcS), and a large subunit (LSU) encoded by a plastid gene (rbcL). Due to its high abundance, Rubisco represents an interesting target to express peptides or small proteins as fusion products at high levels. In an attempt to modify the plant metal content, a polyhistidine sequence was fused to Rubisco, the most abundant protein of plants. Plastid transformation was used to express a polyhistidine (6x) fused to the C-terminal extremity of the tobacco LSU. Transplastomic tobacco plants were generated by cotransformation of polyethylene glycol-treated protoplasts using two vectors: one containing the 16SrDNA marker gene, conferring spectinomycin resistance, and the other the polyhistidine-tagged rbcL gene. Homoplasmic plants containing L8-(His)6S8 as a single enzyme species were obtained. These plants contained normal Rubisco amounts and activity and displayed normal photosynthetic properties and growth. Interestingly, transplastomic plants accumulated higher zinc amounts than the wild-type when grown on zinc-enriched media. The highest zinc increase observed exceeded the estimated chelating ability of the polyhistidine sequence, indicating a perturbation in intracellular zinc homeostasis. We discuss the possibility of using Rubisco to express foreign peptides as fusion products and to confer new properties to higher plants.

Journal Article↗

Integrons and gene cassettes in clinical isolates of co-trimoxazole-resistant Gram-negative bacteria.

Despite a trend of declining consumption, resistance to co-trimoxazole has increased during a 12-year period in Stockholm. The molecular background to this surprising development was investigated by using PCR to screen for integrons and specific resistance genes, followed by sequence analysis of selected integrons, in 105 clinical urinary isolates of Gram-negative bacteria selected partly for trimethoprim resistance. Sixty-five integrons of class 1 or 2 were detected in a subset of 59 isolates, and of these positive isolates, all but one were resistant to trimethoprim. However, 11 isolates were resistant to trimethoprim, but negative for integrons. Isolates positive for integrons were resistant to an average of 4.2 antibiotics, compared with 1.9 antibiotics for integron-negative isolates. Despite this, the only gene cassettes identified in 19 class 1 integrons analysed were dfr and aadA cassettes. Thus, only resistance to trimethoprim, streptomycin, spectinomycin and sulphonamides could be explained by the presence of integrons in these isolates. A new dfr gene, named dfrA22, was discovered as a single gene cassette in a class 1 integron. In addition, sulphonamide resistance in many isolates was caused by carriage of sul2, which has no known association with integrons. Resistance to co-trimoxazole and many other antibiotics was thus not accounted for fully by the presence of integrons in these isolates.

Base Sequence↗

Genetic analysis of a multiresistant strain of Pseudomonas aeruginosa producing PER-1 beta-lactamase.

A multiresistant strain of Pseudomonas aeruginosa, PA2345, belonging to serotype O:1, was isolated at the Teaching Hospital of Besançon, France. Resistance to beta-lactams, including third-generation cephalosporins, depended upon a chromosomally-located composite transposon carrying the bla(PER-1) gene encoding extended-spectrum beta-lactamase PER-1. PA2345 was unrelated genotypically to two previous PER-1-producing isolates of P. aeruginosa. Sequence analysis of the transposon in PA2345 revealed the presence of two insertion sequences (ISPa23 and ISPa24) with very different predicted transposases (TnpA1, TnpA2), which were both bordered by closely related 16-bp inverted repeats. High resistance of PA2345 to aminoglycosides was caused, in part, by a chromosomal class-I integron containing gene cassettes aadB, encoding an ANT(2'') enzyme, and aadA11, encoding a new ANT(3'') enzyme with 281 amino-acids that conferred elevated resistance to streptomycin and spectinomycin. Stable overproduction of efflux system MexXY contributed to resistance to amikacin, while mutations in the quinolone resistance-determining regions of gyrA and parC accounted for the high resistance of PA2345 to fluoroquinolones. The study indicates that multidrug resistance in P. aeruginosa might arise from sequential acquisition of a variety of mechanisms provided by both horizontal gene transfers and mutations in chromosomal genes.

Drug Resistance, Multiple, Bacterial↗

Cloning of a probe for a previously undescribed enterobacterial tetracycline resistance gene.

An 8.35 kb BamHI fragment was cloned from the plasmid R714a. It encoded resistances to chloramphenicol, streptomycin, spectinomycin and tetracycline. Tetracycline resistance was determined by a locus without homology to the known enterobacterial gene classes, TetA-TetE. Further subcloning of the fragment located an unusual tetracycline resistance gene on a 4.7 kb BamHI-BglII fragment. A physical-genetic map of this fragment indicated that the gene was bisected by a PstI site. Deletion analysis and insertion mutagenesis were used to define a suitable probe. An intragenic PstI-AvaI fragment of 1.2 kb was identified, and used as a non-radioactive probe, being specific for this previously undescribed enterobacterial Tet gene.

Cloning, Molecular↗