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Biomedical subjects

E Z Ron

Publications and source records attributed to E Z Ron.

At least 55 records · Page 3Linked to original sources
PubMed1995

Heat shock-dependent transcriptional activation of the metA gene of Escherichia coli.

In Escherichia coli, the growth rate at elevated temperatures is controlled by the availability of endogenous methionine, which is limited because of the temperature sensitivity of the metA gene product, homoserine transsuccinylase (HTS). In order to determine the relationship between this control mechanism and the heat shock response, we estimated the cellular levels of HTS during heat shock by Western (immunoblot) analysis and found an increase following induction by temperature shift and by addition of ethanol or cadmium ions. The elevated level of HTS was a result of transcriptional activation of the metA gene. This activation was heat shock dependent, as it did not take place in rpoH mutants, and probably specific to the metA gene, as another gene of the methionine regulon (metE) was not activated. These results suggest a metabolic link between the two systems that control the response of E. coli to elevated temperatures: the metA gene, which codes for the enzyme responsible for regulating cell growth as a function of temperature elevation (HTS), is transcriptionally activated by the heat shock response.

Acyl Coenzyme A↗
PubMed1994

Azide-resistant mutants in Acinetobacter calcoaceticus A2 are defective in protein secretion.

Azide, an inhibitor of ATPase, and a specific inhibitor of protein export was used in order to select for protein secretion mutants in Acinetobacter calcoaceticus A2. Two such mutants were isolated that were azide-resistant and defective in the general protein transport system. The mutation also conferred additional phenotypic changes, including an inability to grow on minimal media or at 40 degrees C. The existence of protein secretion mutants with a selectable phenotype may be useful for the genetic study of protein export.

Acinetobacter calcoaceticus↗
PubMed1994

Production and Secretion of the Polysaccharide Biodispersan of Acinetobacter calcoaceticus A2 in Protein Secretion Mutants.

Biodispersan is an extracellular anionic polysaccharide produced by Acinetobacter calcoaceticus A2 that changes the surface properties of limestone and acts both as a dispersant and as a grinding aid (E. Rosenberg, C. Rubinovitz, A. Gottlieb, S. Rosenhak, and E. Z. Ron, Appl. Environ. Microbiol. 54:317-322, 1988; E. Rosenberg, C. Rubinovitz, R. Legmann, and E. Z. Ron, Appl. Environ. Microbiol. 54:323-326, 1988; E. Rosenberg, Z. Schwartz, A. Tenenbaum, C. Rubinovitz, R. Legmann, and E. Z. Ron, J. Dispersion Sci. Technol. 10:241-250, 1989). Extracellular fluid also contains a high concentration of secreted proteins that create problems in the purification and application of biodispersan. In order to obtain preparations of biodispersan that contained smaller amounts of protein, we selected mutants of strain A2 that were defective in protein secretion. These mutants produced equal, or even higher, levels of total biodispersan compared with those of the parental strain. Moreover, although there was a significant drop in the concentration of extracellular proteins in the medium, the secretion of biodispersan was unaffected. These results suggest that secretion mutants are potentially useful for the production of extracellular polysaccharides.

Journal Article↗
PubMed1993

Induction of cadmium tolerance in Escherichia coli K-12.

Cadmium ions are bacteriocidal, resulting in exponential killing that starts immediately after exposure. We have shown that pretreatment with sublethal concentrations of cadmium induces cadmium tolerance. Protection against cadmium killing can also be obtained by preincubation at elevated temperatures, known to induce the heat-shock response. However, in contrast to pretreatment at elevated temperatures, exposure to sublethal cadmium concentrations does not induce thermotolerance.

Cadmium↗
PubMed1993

Cloning, sequencing, and transcriptional analysis of the gene coding for the vegetative sigma factor of Agrobacterium tumefaciens.

The sigA gene of Agrobacterium tumefaciens was cloned and sequenced. Comparison with previously analyzed sigA genes revealed a high degree of similarity in nucleotide and amino acid sequences of regions two, three, and four of vegetative sigma factors. However, the upstream regulatory region shows no sequence homology with the Escherichia coli heat shock (sigma 32) promoters. It also does not contain the hairpin-loop structure (inverted repeat sequence) that was found in the upstream region of the groE operon in A. tumefaciens. The transcription initiation site of the gene was determined and found to be at the same position during normal growth and under heat shock conditions. Furthermore, no heat shock activation was observed at the transcriptional level.

Agrobacterium tumefaciens↗
PubMed1993

Heat shock transcription of the groESL operon of Agrobacterium tumefaciens may involve a hairpin-loop structure.

The groESL operon of Agrobacterium tumefaciens was cloned and sequenced and found to be highly homologous to previously analyzed groE operons in nucleotides of the coding region and in amino acid sequence. Transcription of this operon in A. tumefaciens was considerably stimulated by heat shock. Primer extension analysis revealed that the groE transcripts from cells under heat shock were initiated from the same promoter (a sigma-70-like promoter) as transcripts from untreated cells, and no sequence homology with the Escherichia coli heat shock promoters was observed. The DNA sequence downstream of the transcription start site contains an inverted repeat that has a strong similarity to other groESL operons of both gram-positive and gram-negative bacteria (such as cyanobacteria and chlamydiae). This conserved region is thought to form a hairpin-loop structure and may play a role in gene regulation during heat shock.

Agrobacterium tumefaciens↗
PubMed1991

A DNA replication gene maps near terC in Escherichia coli K12.

Temperature-sensitive mutants that filamented at the non-permissive temperature were isolated by specific mutagenesis of the terminus region of the Escherichia coli chromosome. Two of them, mapping at about 35 min, failed to divide due to inhibition of DNA replication. Further characterization indicated that these mutants are temperature-sensitive for DNA chain elongation.

Chromosome Mapping↗
PubMed1990

Adherence pili of avian strains of Escherichia coli O78.

Avian colisepticemia starts with the invasion of the trachea by virulent strains of Escherichia coli, with strains of serotype O78 responsible for about 50% of the cases. Several O78 strains isolated from poultry with colisepticemia produced pili with a subunit of molecular weight of 18,000 that mediated adherence to avian epithelial tissues in vitro and in vivo.

Animals↗
PubMed1989

Termination of DNA replication is required for cell division in Escherichia coli.

The correlation between termination of DNA replication and cell division in Escherichia coli was studied under conditions in which DNA replication was slowed down without inducing SOS functions. The experimental system used involved amino acid starvation of synchronized cells in the presence of methionine. The results further support the essential correlation between termination of DNA replication and initiation of division processes.

Cell Division↗
PubMed1989

Apparent minimal size required for cell division in Escherichia coli.

The experiments described in this report were designed to find out whether there is a minimal size threshold for cell division or for DNA replication in Escherichia coli. Cells with decreasing size (or mass) were obtained by successive amino acid starvations. Following two starvations, the cells were at least 30% smaller than unstarved newborn cells. The results suggest that this size is below a minimal size threshold for cell division but not for initiation of DNA replication.

Amino Acids↗
PubMed1988

Production of Biodispersan by Acinetobacter calcoaceticus A2.

Bacterial strains A2 and HE5, isolated by enrichment culture techniques, were shown to produce extracellular, nondialyzable materials which disperse limestone powders in water. These materials are referred to as biodispersans. Strains A2 and HE5 were classified as Acinetobacter calcoaceticus by physiological and genetic tests. An assay for limestone-dispersing activity was developed which is based on the settling time of a standard 10% limestone-in-water mixture. The assay was proportional to biodispersan concentration between 40 and 100 mug/ml. Dispersion was optimum between pH 9 and 12. Phosphate (2 mM) and magnesium (8 mM) ions caused a 50% inhibition of activity. An optimized medium for the production of biodispersan was developed with ethanol as the substrate. Biodispersan was produced only after the bacteria completed their exponential growth phase and continued during the stationary phase, reaching over 4 g of crude biodispersan per liter.

Journal Article↗
PubMed1988

Purification and Chemical Properties of Acinetobacter calcoaceticus A2 Biodispersan.

The extracellular dispersant of Acinetobacter calcoaceticus A2, referred to as biodispersan, was concentrated by ammonium sulfate precipitation and deproteinized by hot phenol treatment. The active component was an anionic polysaccharide (PS-A2). The specific activity of PS-A2 was approximately three times greater than that of crude biodispersan. PS-A2 had a sedimentation constant of 1.39 S, a diffusion coefficient of 18.8 x 10 cm s, and a partial molar volume of 0.65 cm g, yielding an average molecular weight of 51,400. Titration of the polymer gave two inflection points: pK(1) = 3.1 (1.15 muEq/mg) and pK(2) = 8.0 (0.4 muEq/mg). PS-A2 slowly consumed 1.10 mumol of periodate per mg. The C nuclear magnetic resonance spectrum of PS-A2 indicated four methyl groups, four carbonyl C atoms, and four signals in the anomeric region (95 to 110 ppm), indicative of the presence of four different monosaccharides. Strong acid hydrolysis of PS-A2 yielded four reducing sugars: glucosamine, a 6-methyl aminohexose, galactosamine uronic acid, and an unidentified amino sugar. Ruthenium red binding to PS-A2 was stoichiometric: 1 molecule of dye bound per 2.0 carboxyl groups.

Journal Article↗
PubMed1984

Regulatory region of the metA gene of Escherichia coli K-12.

Transcription of the metA gene of Escherichia coli K-12 is from a promoter which is under methionine control and is located next to a region which has an extensive sequence homology with the operator regions of the metBL and metF genes. However, in the metA gene there is a second transcription start point which is located 74 base pairs upstream and which is independent of the intracellular methionine concentration.

Acyltransferases↗