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Volume 143,
Issue 4,
1997
Volume 143, Issue 4, 1997
- Genetics And Molecular Biology
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The temperature sensitivity of Bacillus subtilis DB1005 is due to insufficient activity, rather than insufficient concentration, of the mutant σA factor
More LessThe σA factor of Bacillus subtilis DB1005 contains two amino acid substitutions (1198A and 1202A) in the promoter –10 binding region. It has been confirmed that this σ factor is responsible for the temperature sensitivity of B. subtilis DB1005. An investigation was conducted into how the mutantσA could cause temperature-sensitive (Ts) cell growth by analysing its structural stability, cellular concentration and transcriptional activity. The mutant σA was unstable even at the permissive temperature of 37°C (t1/2 59 min), whereas the wild-type counterpart was fairly stable under the same conditions (t 1/2 600 min). However, neither wild-type σA nor mutant σA was stable at 49°C (t 1/2 34 min and 23 min, respectively). Analyses of the rates of σA synthesis revealed that B. subtilis DB1005 was able to compensate for unstable σ by elevating the level of σA at 37°C but not at 49°C. Moreover, overexpression of the mutant σA at 49°C could not suppress the Ts phenotype of B. subtilis DB1005. This indicates that the temperature sensitivity of B. subtilis DB1005 is not due to insufficient σA concentration in the cell. The greater decline of an already reduced activity of the mutant σA at 49°C suggests that the temperature sensitivity of B. subtilis DB1005 is instead the result of a very low activity of σ A probably below a critical level necessary for cell growth.
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The Bacillus subtilis clpC operon encodes DNA repair and competence proteins
More LessClpC of Bacillus subtilis, controlling competence gene expression and survival under stress conditions, is encoded by the fourth gene of a six-gene operon. The product of orf1 contains a potential helix-turn-helix motif, but shows no significant similarities with known protein sequences. The second and third genes encode proteins with similarities to zinc-finger proteins (orf2) and arginine kinases (orf3), respectively. The product of orf5 contains a zinc-finger motif and an ATP-binding domain, and is highly similar to the product of the Escherichia coli sms gene. A strain bearing a disruption of orf5 showed increased sensitivity to the alkylating agent methyl methanesulfonate. Furthermore, this mutant strain displayed decreased capacity for genetic recombination as measured by transformation experiments. The last open reading frame, orf6, encodes a protein with limited similarity in its C-terminal part to the B. subtilis comEA gene product and to the UvrC DNA repair excinuclease. Inactivation of orf5 resulted in strongly diminished transformation with all types of DNA. Mutations affecting either orf5 or orf6 resulted in strains with decreased resistance to UV-irradiation in the stationary phase, indicating that these proteins play a role in the development of a nonspecific stationary-phase resistance to UV-irradiation. Moreover, these results suggest an involvement of both proteins in transformation and presumably in DNA repair.
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Molecular characterization of the bet genes encoding glycine betaine synthesis in Sinorhizobium meliloti 102F34
As a first step towards the elucidation of the molecular mechanisms responsible for the utilization of choline and glycine betaine (betaine) either as carbon and nitrogen sources or as osmoprotectants in Sinorhizobium meliloti, we selected a Tn5 mutant, LTS23-1020, which failed to grow on choline but grew on betaine. The mutant was deficient in choline dehydrogenase (CDH) activity, failed to oxidize [methyl-14C]choline to [methyl-14C]betaine, and did not use choline, but still used betaine, as an osmoprotectant. The Tn5 mutation in LTS23-1020 was complemented by plasmid pCH034, isolated from a genomic bank of S. meliloti 102F34. Subcloning and DNA sequencing showed that pCH034 harbours two ORFs which showed 60% and 57% identity with the Escherichia coli betB gene encoding betaine-aldehyde dehydrogenase (BADH) and betA gene encoding CDH, respectively. In addition to the homology with E. coli genes, the deduced sequence of the sinorhizobial BADH protein displays consensus sequences also found in plant BADHs. The deduced sequence of the sinorhizobial CDH protein shares only 21% identical residues with choline oxidase from Arthrobacter globiformis. The structural organization of the betBA genes in S. meliloti differs from that described in E. coli: (i) the two ORFs are separated by a 210 bp sequence containing inverted repeats ressembling a putative rho-independent transcription terminator, and (ii) no sequence homologous to betT (high-affinity choline transport system) or betI (regulator) was found in the vicinity of the sinorhizobial betBA genes. Evidence is also presented that the S. meliloti betBA genes are not located on the megaplasmids.
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- Pathogenicity And Medical Microbiology
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The ability of Escherichia coli O157:H7 to decrease its intracellular pH and resist the toxicity of acetic acid
More LessBatch cultures of Escherichia coli K-12 grew well in an anaerobic glucose medium at pH 5.9, but even small amounts of acetate (20 mM) inhibited growth and fermentation. E. coli O157:H7 was at least fourfold more resistant to acetate than K-12. Continuous cultures of E. coli K-12 (pH 5.9, dilution rate 0.085 h-1) did not wash out until the sodium acetate concentration in the input medium was 80 mM, whereas E. coli O157:H7 persisted until the sodium acetate concentration was 160 mM. E. coli K-12 cells accumulated as much as 500 mM acetate, but the intracellular acetate concentration of O157:H7 was never greater than 300 mM. Differences in acetate accumulation could be explained by intracellular pH and the transmembrane pH gradient (δpH). E. coli K-12 maintained a more or less constant δpH (intracellular pH 6.8), but E. coli O157:H7 let its δpH decrease from 0.9 to 0.2 units as sodium acetate was added to the medium. Sodium acetate increased the rate of glucose consumption, but there was little evidence to support the idea that acetate was creating a futile cycle of protons. Increases in glucose consumption rate could be explained by increases in D-lactate production and decreases in ATP production. Intracellular acetate was initially lower than the amount predicted by ∆pH, but intracellular acetate and δpH were in equilibrium when the external acetate concentrations were high. Based on these results, the acetate tolerance of O157:H7 can be explained by fundamental differences in metabolism and intracellular pH regulation. By decreasing the intracellular pH and producing large amounts of D-lactate, O157:H7 is able to decrease δpH and prevent toxic accumulations of intracellular acetate anion.
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Homologous regions of the Salmonella enteritidis virulence plasmid and the chromosome of Salmonella typhi encode thiol: disulphide oxidoreductases belonging to the DsbA thioredoxin family
More LessThe nucleotide sequence relatedness between the chromosome of Salmonella typhi and the virulence plasmid of Salmonella enteritidis was investigated using short DNA probes of < 2 kb covering the whole virulence plasmid sequence. Only one homologous region was detected. This region was subsequently cloned and partially sequenced. Sequences closely related to the pefl gene and the ORFs orf7, orf8 and orf9, which are located downstream of the fimbrial pef operon of the Salmonella typhimurium virulence plasmid, were detected. Sequencing of the cloned S. typhi DNA fragment also revealed identity with genes of the fimbrial sef operon characterized in the chromosome of S. enteritidis. These nucleotide sequences mapped upstream of the S. typhi chromosomal region homologous to the S. enteritidis virulence plasmid. The general organization of the cloned S. typhi chromosomal fragment was similar to the fimbriae-encoding region of the S. typhimurium virulence plasmid. The deduced product of orf8 in the S. typhimurium virulence plasmid, as well as those of the corresponding ORFs in the homologous region of the S. typhi chromosome and in the S. enteritidis virulence plasmid (designated dlt and dlp, respectively), appeared to be related to the thioredoxin family of thiol:disulphide oxidoreductases. The dlp gene was able to complement the DTT-sensitive phenotype, the inability to metabolize glucose 1-phosphate and the low alkaline phosphatase activity of a dsbA mutant of Escherichia coli. The dlt gene partially complemented the lack of alkaline phosphatase activity, but not the other mutant phenotypes. The products of both genes could be detected using the T7 RNA polymerase promoter expression system. The estimated molecular masses of the products of the dlt and dlp genes by SDS-PAGE were 26 and 23 kDa, respectively, the first being in agreement with the deduced amino acid sequence and the latter, somewhat smaller. The processing of a possible leader peptide in the Dlp protein, but not in the Dlt protein, could be responsible for this difference. The Dlp protein appeared as a doublet band on SDS-PAGE, which is characteristic of the oxidized and reduced states of this kind of protein.
The EMBL accession numbers for the sequences of dlt and dlp reported in this paper are X94325 and X94326, respectively.
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Variation within serovars of Neisseria gonorrhoeae detected by structural analysis of outer-membrane protein PIB and by pulsed-field gel electrophoresis
More LessOuter-membrane protein PI is the antigen responsible for serovar specificity of Neisseria gonorrhoeae and is a potential vaccine target. In order to investigate possible hidden variation within a serovar, the sequence of the por genes encoding protein PIB have been obtained from a series of strains, including isolates known to be epidemiologically linked. The inferred amino acid sequences of the PIB molecules of isolates from known sexual contacts were identical, but non-related isolates showed significant heterogeneity in PIB sequence. These differences were not confined to the two variable regions (Var1 and Var2) which have previously been identified, but were largely, although not exclusively, located in regions predicted to form one of eight surface-exposed loops. The isolates were subjected to pulsed-field gel electrophoresis of restriction digests of chromosomal DNA, which also demonstrated identity between linked strains but revealed diversity within a serovar. The deduced amino acid sequences of PIB were also used to synthesize peptides for epitope-mapping experiments. These revealed that some mAbs, used to define serovar specificity, recognized linear epitopes located in loops 5 and 6, while others appeared to recognize conformational epitopes elsewhere in the molecule. The occurrence of the sequence differences within a serovar, which are not detected by the serotyping reagents, reveals that PIB represents a potential source of information which should permit considerably more detailed epidemiological studies than are currently possible and focuses attention on more conserved regions of the protein as potential targets for vaccination.
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Differences in genetic diversity of nonecapsulated Haemophilus influenzae from various diseases
More LessGenetic relationships among 80 isolates of nonencapsulated Haemophilus influenzae recovered from different disease types were determined by multilocus enzyme electrophoresis (MEE) at 13 enzyme loci in an attempt to assess the association between multilocus genotype and disease. The isolates were obtained from 15 patients with meningitis, 10 with otitis media, 19 with chronic bronchitis, 20 with cystic fibrosis, and 16 were obtained from healthy carriers. The 80 isolates were assigned to 69 electrophoretic types (ETs) falling into 5 groups. Isolates from each disease entity were represented by a variety of genotypes; however, cluster analysis from a matrix of genetic distances between ETs revealed that the ETs of the otitis media and meningitis isolates were all clustered within a genetic distance of 0∙55 (group 1). In addition, no genotypes were shared between H. influenzae carrier isolates and isolates from cases of disease. H. influenzae isolates from healthy individuals were distributed significantly differently from those from chronic bronchitis meningitis and otitis media patients. The genetic diversity (H) of carrier strains was greatest, although not statistically different from that of isolates from patients with disease. It was concluded that the genetic distribution of acute disease isolates is not random over the five ET groups, although the genetic diversity within the groups is not different. The effect of bacterial persistence in the host on the genetic diversity of H. influenzae is discussed.
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- Physiology And Growth
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Photoreactivation in an archaeon from geothermal environments
More LessUV-inactivated cells of Sulfolobus acidocaldarius rapidly regained viability when exposed to white light This recovery was strictly dependent upon illumination with visible light and was not attenuated by prior dark-incubation. The kinetics of photoreactivation were determined at several temperatures and at several wavelengths of light. The results obtained in vivo were consistent with a DNA photolyase having a broad action spectrum. Photoreactivation of S. acidocaldarius apparently represents the first DNA repair process to be measured in an archaeon which grows optimally near 80°C.
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Expression analysis of the ssgA gene product, associated with sporulation and cell division in Streptomyces griseus
More LessThe ssgA gene of Streptomyces griseus B2682, when present in high copy number, results in both suppression of sporulation and fragmented growth of mycelia. Western analysis with polyclonal antibodies against the gene product (SsgA) revealed a close correlation between SsgA accumulation and the onset of sporulation in wild-type cells. The protein was only detected in the cytoplasm. Certain developmental mutants of S. griseus (afs, relC and brgA) which are defective in aerial mycelium formation in solid culture and submerged spore formation in liquid culture failed to accumulate SsgA. The SsgA protein appeared shortly (1 h) after nutritional shift-down of strain B2682 cells, afs mutant cells sporulated and expressed SsgA only when A-factor was present both before and after nutritional shift-down. Introduction of the ssgA gene in a low-copy-number vector into strain B2682 resulted in fivefold overexpression of SsgA, and was accompanied by fragmented growth of mycelia and suppression of submerged spore formation (in liquid culture) and aerial mycelium formation (in solid culture). Streptomycin production was not inhibited. In a control experiment, a nonfunctional ssgA gene possessing a frameshift mutation near its N-terminus had no effect on either growth or sporulation. It is proposed that the ssgA gene product plays a role in promoting the developmental process of S. griseus.
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An interfacial uptake mechanism for the degradation of pyrene by a Rhodococcus strain
More LessThe mechanism of uptake of polycyclic aromatic hydrocarbons (PAHs) was studied using a kinetic approach by electrolytic respirometry. In the case of the degradation of pyrene dissolved in a non-water-soluble non-degradable solvent (2,2,4,4,6,8,8-heptamethylnonane), by a Rhodococcus sp., two successive phases of exponential growth, during which over 80% of substrate degradation took place, were clearly characterized. During the second phase of biodegradation, rates of pyrene uptake were higher than those determined in abiotic conditions for the physicochemical transfer of pyrene from the solvent to the aqueous phase and no evidence for the presence of glycolipidic biosurfactants was obtained. The value of the specific growth rate for the first phase (𝜇max) was independent of the volume of the solvent phase and of the concentration of pyrene and was, in all cases, higher than that for the second phase (𝜇i). The 𝜇i values increased with the volume of the solvent phase but were independent of pyrene concentration, a clear indication of an interfacial uptake mechanism. The experimental kinetic data fitted well with a mathematical model incorporating PAH uptake both from the interface and from the aqueous medium by a population consisting of adsorbed cells in dynamic equilibrium with the cells in the aqueous medium, interfacial uptake being predominant in these experiments. Similar results were obtained for the degradation of fluoranthene. This newly demonstrated mechanism of PAH uptake is of great significance for the degradation of higher PAHs.
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Pyruvate carboxylase as an anaplerotic enzyme in Corynebacterium glutamicum
More LessThe recent discovery that phosphoenolpyruvate carboxylase (PEPCx) is dispensable for growth and lysine production in Corynebacterium glutamicum implies that this organism possesses (an) alternative anaplerotic enzyme(s). In permeabilized cells of C. glutamicum, we detected pyruvate carboxylase (PCx) activity. This activity was effectively inhibited by low concentrations of ADP, AMP and acetyl-CoA. PCx activity was highest [45 ± 5 nmol min−1 (mg dry wt)−1] in cells grown on lactate or pyruvate, and was about two- to threefold lower when the cells were grown on glucose or acetate, suggesting that formation of PCx is regulated by the carbon source in the growth medium. In cells grown at low concentrations of biotin (< 5 μg I−1), PCx activity was drastically reduced, indicating that the enzyme is a biotin protein. Growth experiments with the wild-type and a defined PEPCx-negative mutant of C. glutamicum on glucose showed that the mutant has a significantly higher demand for biotin than the wild-type, whereas both strains have the same high biotin requirement for growth on lactate and the same low biotin requirement for growth on acetate. These results indicate that (i) PCx is an essential anaplerotic enzyme for growth on glucose in the absence of PEPCx, (ii) PCx is an essential anaplerotic enzyme for growth on lactate even in the presence of PEPCx, and (iii) PCx has no anaplerotic significance for growth on acetate as the carbon source. In support of these conclusions, screening for clones unable to grow on a minimal medium containing lactate, but able to grow on a medium containing glucose or acetate, led to the isolation of PCx-defective mutants of C. glutamicum.
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Effects of alternative methyl group acceptors on the growth energetics of the O-demethylating anaerobe Holophaga foetida
More LessThe anaerobic bacterium Holophaga foetida can metabolize the methyl groups of methoxylated aromatic compounds either to acetate or to dimethyl sulphide. The effects of this metabolic flexibility were investigated under conditions of excess; substrate (batch culture) and substrate limitation (chemostat culture). Growth yield data suggest that transfer of the methyl groups to sulphide, in contrast to the homoacetogenic transfer to CO2, was not coupled to energy conservation. Under conditions of excess substrate, methyl groups were quantitatively transferred to sulphide. Growth yields decreased but growth rates increased upon the addition of sulphide during exponential growth in pH- and sulphide-regulated batch cultures. From the measured growth yields, the Gibbs free energy dissipation of catabolism plus anabolism (
) was calculated using stoichiometric equations incorporating biomass formation (macrochemical equations). The observed increase in growth rate correlated well with an increase in
, suggesting a relationship between growth kinetics and growth energetics. During steady-state growth in pH- and sulphide-regulated chemostat culture, a considerable fraction of the methyl groups was converted to acetate, despite the presence of sulphide. This resulted in similar growth yields and correspondingly similar
values in the presence and absence of sulphide. Apparently, H. foetida uncouples catabolism and anabolism in batch culture under conditions of excess substrate to a greater extent than in the chemostat under substrate limitation, by transferring the methyl groups quantitatively to sulphide and thereby dissipating the Gibbs free energy change of the methyl transfer. The physiological significance of these findings could be that H. foetida adjusts the energetics of its metabolism to the growth conditions (i) to maximize the growth rate if substrate is available in excess or, (ii) to maximize the growth yield if substrate is limiting.
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Periplasmic cyclic 1,2-β-glucan in Brucella spp. is not osmoregulated
More LessBiosynthesis of periplasmic cyclic 1,2-β-glucans in Brucella ovis strain REO198 and B. abortus strain S19 was found to be carried out by membrane-bound enzymes that use UDP-glucose (UDP-Glc) as donor substrate. Contrary to what happens in species of the genera Agrobacterium and Rhizobium, the accumulation of the reaction products in Brucella appeared not to be osmoticaliy regulated. Incubation of permeabilized cells with UDP-[14C]Glc led to the formation of soluble neutral cyclic 1,2-β-glucans and [14C]glucose-labelled glucoproteins. PAGE of pulse–chase experiments carried out with permeabilized cells showed that the molecular mass of the labelled protein was indistinguishable from Agrobacterium tumefaciens A348 and Rhizobium fredii USDA191 glucoproteins known to be intermediates in the synthesis of cyclic glucans. Brucella total membrane preparations were less efficient than permeabilized cells in the formation of cyclic glucan; this was attributed to defective cyclization. Accumulation of protein intermediates having oligosaccharides of high molecular mass that were not released from the protein was observed after chase with 2 mM UDP-Glc. This defect was not observed when permeabilized cells were used as enzyme preparation, thus suggesting that in Brucella a factor(s) that was lost or inactivated upon the preparation of membranes was required for the effective regulation between elongation and cyclization reactions.
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Comparative physiology of salt tolerance in Candida tropicalis and Saccharomyces cerevisiae
More LessThe salt tolerance of the respiratory yeast Candida tropicalis and the fermentative yeast Saccharomyces cerevisiae have been compared in glucose media. C. tropicalis showed a better adaptation to Na+ and Li+ and maintained higher intracellular K+:Na+ and K+:Li+ ratios than S. cerevisiae However, C. tropicalis showed a poorer adaptation to osmotic stress (produced by KCI and sorbitol) and exhibited reduced glycerol production as compared to S. cerevisiae In media with the non-repressing sugar galactose as carbon source, S. cerevisiae exhibited reduced glycerol production and increased sensitivity to osmotic stress. Under these conditions, S. cerevisiae, but not C. tropicalis, utilized trehalose as a more important osmolyte than glycerol. These results suggest that the relative tolerance of yeast to the osmotic and cation toxicities of NaCl, and the underlying relative capabilities for osmolyte synthesis and cation transport, are modulated by the general catabolite control exerted by glucose.
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Metabolic flux response to salt-induced stress in the halotoleirant yeast Debaryomyces hansenii
More LessThe toxic effect of NaCl and KCI on growth of the marine yeast Debaryomyces, hansenii on glucose or glycerol was studied. Above a threshold value, both salts reduced the specific growth rate, specific glucose and glycerol respiration rates and specific glucose fermentation rate, as well as biomass yields. The exponential inhibition constant, k, and minimum toxic concentration, c min, were similar for all physiological parameters assayed. The effect of either salt on the specific activity of several glycolytic enzymes showed a similar inhibition pattern, although at much lower salt concentrations compared with the physiological parameters. In agreement with published results on glycerol phosphate dehydrogenase stimulation by salt, we present evidence that a general glycolytic flux deviation could occur naturally during salt stress, due to the intrinsic sensitivity of the glycolytic enzymes to intracellular ion concentrations.
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- Plant-Microbe Interactions
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The soybean cultivar specificity gene noIX is present, expressed in a nodD-dependent manner, and of symbiotic significance in cultivar-nonspecific strains of Rhizobium (Sinorhizobium) fredii
More LessRhizobium (now Sinorhizobium) fredii is a symbiotic nitrogen-fixing bacterium that can nodulate soybean in a cultivar-specific manner. This process is governed by a set of negatively acting nodulation genes termed noIXWBTUV. These genes prevent R. fredii strain USDA257 from infecting soybean cultivars such as McCall, but they do not block nodulation of cultivar Peking. R. fredii strain USDA191 contains DNA sequences that hybridize to noIXWBTUV, yet it forms normal nitrogen-fixing nodules on both McCall and Peking soybean. These sequences were isolated and their structure and function examined in comparison to noIXWBTUV of strain USDA257. Restriction maps of the two loci are identical, as is a 2∙4 kb DNA sequence that corresponds to noIX and its promoter region. Expression of noIX by strain USDA191 is flavonoid-dependent in culture and readily detectable in nodules. The gene is not inducible in a mutant of strain USDA191 that lacks the regulatory nodD1 gene, and its expression is greatly attenuated in a nodD2 mutant. noIX is also present and flavonoid-inducible in HH103, a second R. fredii strain that nodulates McCall soybean normally. Inactivation of noIX in strain HH103, USDA191 or USDA257 leads to retardation of initial nodulation rates on soybean cultivars such as Peking and to acquisition of the capacity to form nitrogen-fixing nodules on two species of Erythrina. noIX is thus of symbiotic significance in all three strains, even though it regulates soybean cultivar specificity only in strain USDA257.
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Identification of genes in Rhizobium leguminosarum bv. trifolii whose products are homologues to a family of ATP-binding proteins
More LessThe specific interaction between rhizobia and their hosts requires many genes that influence both early and late steps in symbiosis. Three new genes, designated prsD, prsE (protein secretion) and orf3, were identified adjacent to the exo133 mutation in a cosmid carrying the genomic DNA of Rhizobium leguminosarum bv. trifolii TA1. The prsDE genes share significant homology to the genes encoding ABC transporter proteins PrtDE from Erwinia chrysanthemi and AprDE from Pseudomonas aeruginosa which export the proteases in these bacteria. PrsD shows at least five potential transmembrane hydrophobic regions and a large hydrophilic domain containing an ATP/GTP binding cassette. PrsE has only one potential transmembrane hydrophobic domain in the N-terminal part and is proposed to function as an accessory factor in the transport system. ORF3, like PrtF and AprF, has a typical N-terminal signal sequence but has no homology to these proteins. The insertion of a kanamycin resistance cassette into the prsD gene of the R. leguminosarum bv. trifolii TA1 wild-type strain created a mutant which produced a normal amount of exopolysaccharide but was not effective in the nodulation of clover plants.
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A secreted aspartic proteinase from Glomerella cingulata: purification of the enzyme and molecular cloning of the cDNA
More LessA secreted aspartic proteinase from Glomerella cingulata (GcSAP) as purified to homogeneity by ion exchange chromatography. The enzyme has an M r of 36000 as estimated by SDS-PAGE, optimal activity from pH 3∙5 to pH 4∙0 and is inhibited by pepstatin. The N-terminal sequence, 23 residues long, was used to design a gene-specific primer. This was used in 3ʹ RACE (rapid amplification of cDNA ends) PCR to amplify a 1∙2 kb fragment of the gcsap DNA. A second gene-specific primer was designed and used in 5ʹ RACE PCR to clone the 5՛ region. This yielded a 600 bp DNA fragment and completed the open reading frame. The gcsap open reading frame encodes a protein with a 78 residue prepro-sequence typical of other fungal secreted aspartic proteinases. Based on the deduced sequence, the mature enzyme contains 329 amino acids and shows approximately 40% identity to other fungal aspartic proteinases. Subsequent cloning and sequencing of gcsap fragments obtained from PCR with genomic DNA revealed a 73 bp intron beginning at nt 728. Southern nalyses at medium and high stringency indicated that G. cingulata possesses ne gene for the secreted aspartic proteinase, and Northern blots indicated that gene expression was induced by exogenous protein and repressed by ammonium salts. GcSAP s a putative pathogenicity factor of G. cingulata, and it will now be possible to create SAP- mutants and assess the role GcSAP lays in pathogenicity.
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- Systematics
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Homologous regions of the Salmonella enteritidis virulence plasmid and the chromosome of Salmonella typhi encode thiol: disulphide oxidoreductases belonging to the DsbA thioredoxin family
More LessDNA sequences of a fragment of nifH from diverse cyanobacteria were amplified, cloned and sequenced to determine the evolutionary relationship of nitrogenase within the cyanobacteria as a group, and to provide a basis for the identification of uncultivated strains of cyanobacteria in the environment. Analysis of 30 nitrogenase DNA and deduced amino acid sequences from cyanobacteria representing five major taxonomic subdivisions showed great variation in phylogenetic distances between the sequences. Sequences from heterocystous cyanobacteria formed a coherent cluster, in which branching forms did not form a clade distinct from the non-branching forms. Nitrogenase sequences from the unicellular cyanobacteria Gloeothece and Synechococcus sp. RF-1 formed a cluster, as did sequences from the genera Xenococcus and Myxosarcina. The nifH sequences of filamentous nonheterocystous cyanobacteria were not closely related to each other, forming deep branches with respect to the heterocystous cyanobacterial nifH sequences. The phylogeny of nifH based on amino acid sequences was consistent with taxonomic relationships among the strains; for example, a sequence obtained from a natural assemblage believed to be dominated by ‘Lyngbya’ clustered with nifH from Lyngbya lagerheimii. Results also indicate that the phylogeny of nifH among the cyanobacteria is largely consistent with the phylogeny of 16S rRNA, and furthermore that the nifH sequence can be used to identify uncultivated strains of nitrogen-fixing cyanobacteria.
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Methylosphaera hansonii gen. nov., sp. nov., a psychrophilic, group I methanotroph from Antarctic marine-salinity, meromictic lakes
More LessMethanotrophic bacteria were enumerated and isolated from the chemocline and surface sediments of marine-salinity Antarctic meromictic lakes located in the Vestfold Hills, Antarctica (68° S 78° E). Most probable number (MPN) analysis indicated that at the chemocline of Ace Lake the methanotroph population made up only a small proportion of the total microbial population and was sharply stratified, with higher populations detected in the surface sediments collected at the edge of Ace Lake and Burton Lake. Methanotrophs were not detected in Pendant Lake. Only a single phenotypic group of methanotrophs was successfully enriched, enumerated and isolated into pure culture from the lake samples. Strains of this group were non-motile, coccoidal in morphology, did not form resting cells, reproduced by constriction, and required seawater for growth. The strains were also psychrophilic, with optimal growth occurring at 10–13°C and maximum growth temperatures of 16–21°C. The ribulose monophosphate pathway but not the serine pathway for incorporation of C1 compounds was detectable in the strains. The guanine plus cytosine (G+C) content of the genomic DNA was 43–46 mol%. Whole-cell fatty acid analysis indicated that 16:1ω8c (37–41%), 16:1ω6c (17–19%), 16:1ω7c (15–19%) and 16:0 (14–15%) were the major fatty acids in the strains. 16S rDNA sequence analysis revealed that the strains form a distinct line of descent in the family Methylococcaceae (group I methanotrophs), with the closest relative being the Louisiana Slope methanotrophic mytilid endosymbiont (91∙8–92∙3% sequence similarity). On the basis of polyphasic taxonomic characteristics the Antarctic lake isolates represent a novel group I methanotrophic genus with the proposed name Methylosphaera hansonii (type strain ACAM 549).
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Volume 79 (1973)
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Volume 78 (1973)
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Volume 77 (1973)
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Volume 76 (1973)
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Volume 75 (1973)
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Volume 74 (1973)
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Volume 73 (1972)
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Volume 72 (1972)
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Volume 71 (1972)
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Volume 70 (1972)
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Volume 69 (1971)
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Volume 68 (1971)
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Volume 67 (1971)
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Volume 66 (1971)
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Volume 65 (1971)
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Volume 64 (1970)
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Volume 63 (1970)
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Volume 62 (1970)
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Volume 61 (1970)
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Volume 60 (1970)
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Volume 59 (1969)
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Volume 58 (1969)
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Volume 57 (1969)
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Volume 56 (1969)
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Volume 55 (1969)
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Volume 54 (1968)
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Volume 53 (1968)
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Volume 52 (1968)
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Volume 51 (1968)
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Volume 50 (1968)
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Volume 49 (1967)
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Volume 48 (1967)
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Volume 47 (1967)
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Volume 46 (1967)
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Volume 45 (1966)
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Volume 44 (1966)
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Volume 43 (1966)
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Volume 42 (1966)
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Volume 41 (1965)
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Volume 40 (1965)
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Volume 39 (1965)
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Volume 38 (1965)
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Volume 37 (1964)
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Volume 36 (1964)
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Volume 35 (1964)
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Volume 34 (1964)
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Volume 33 (1963)
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Volume 32 (1963)
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Volume 31 (1963)
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Volume 30 (1963)
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Volume 29 (1962)
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Volume 28 (1962)
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Volume 27 (1962)
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Volume 26 (1961)
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Volume 25 (1961)
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Volume 24 (1961)
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Volume 23 (1960)
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Volume 22 (1960)
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Volume 21 (1959)
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Volume 20 (1959)
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Volume 19 (1958)
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Volume 18 (1958)
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Volume 17 (1957)
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Volume 16 (1957)
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Volume 15 (1956)
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Volume 14 (1956)
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Volume 13 (1955)
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Volume 12 (1955)
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Volume 11 (1954)
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Volume 10 (1954)
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Volume 9 (1953)
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Volume 8 (1953)
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Volume 7 (1952)
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Volume 6 (1952)
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Volume 5 (1951)
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Volume 4 (1950)
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Volume 3 (1949)
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Volume 2 (1948)
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Volume 1 (1947)
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