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Biomedical subjects

I Mahler

Publications and source records attributed to I Mahler.

At least 19 recordsLinked to original sources
PubMed1998

Phosphatase activity and lead resistance in Citrobacter freundii and Staphylococcus aureus.

It has been previously reported that strains of Citrobacter freundii and of Staphylococcus aureus accumulated lead as Pb-phosphate when grown on media supplemented with high levels of lead salts. Phosphatase activity, which has been postulated to be involved in lead accumulation, was unrelated to lead resistance, resistant and sensitive cells displaying similar levels and patterns of enzyme activity.

Citrobacter freundii↗
PubMed1996

Lead resistance and sensitivity in Staphylococcus aureus.

Five lead-resistant strains of Staphylococcus aureus were isolated. Plasmid-free lead-sensitive variants were obtained from the three plasmid-bearing strains. Lead-resistant strains tolerated an approximately 600 x higher Pb(NO3)2 concentration than lead-sensitive strains. Both types of strains initially bound lead, but only the resistant strains accumulated the metal as an intracellular lead-phosphate.

Bacteriological Techniques↗
PubMed1989

Homologous metalloregulatory proteins from both gram-positive and gram-negative bacteria control transcription of mercury resistance operons.

We report the overexpression, purification, and properties of the regulatory protein, MerR, for a chromosomally encoded mercury resistance determinant from Bacillus strain RC607. This protein is similar in sequence to the metalloregulatory proteins encoded by gram-negative resistance determinants found on transposons Tn21 and Tn501 and to a predicted gene product of a Staphylococcus aureus resistance determinant. In vitro DNA-binding and transcription experiments were used to demonstrate those purified Bacillus MerR protein controls transcription from a promoter-operator site similar in sequence to that found in the transposon resistance determinants. The Bacillus MerR protein bound in vitro to its promoter-operator region in both the presence and absence of mercuric ion and functioned as a negative and positive regulator of transcription. The MerR protein bound less tightly to its operator region (ca. 50- to 100-fold) in the presence of mercuric ion; this reduced affinity was largely accounted for by an increased rate of dissociation of the MerR protein from the DNA. Despite this reduced DNA-binding affinity, genetic and biochemical evidence support a model in which the MerR protein-mercuric ion complex is a positive regulator of operon transcription. Although the Bacillus MerR protein bound only weakly to the heterologous Tn501 operator region, the Tn501 and Tn21 MerR proteins bound with high affinity to the Bacillus promoter-operator region and exhibited negative, but not positive, transcriptional control.

Amino Acid Sequence↗
PubMed1989

Nucleotide sequence of a chromosomal mercury resistance determinant from a Bacillus sp. with broad-spectrum mercury resistance.

A 13.5-kilobase HindIII fragment, bearing an intact mercury resistance (mer) operon, was isolated from chromosomal DNA of broad-spectrum mercury-resistant Bacillus sp. strain RC607 by using as a probe a clone containing the mercury reductase (merA) gene. The new clone, pYW33, expressed broad-spectrum mercury resistance both in Escherichia coli and in Bacillus subtilis, but only in B. subtilis was the mercuric reductase activity inducible. Sequencing of a 1.8-kilobase mercury hypersensitivity-producing fragment revealed four open reading frames (ORFs). ORF1 may code for a regulatory protein (MerR). ORF2 and ORF4 were associated with cellular transport function and the hypersensitivity phenotype. DNA fragments encompassing the merA and the merB genes were sequenced. The predicted Bacillus sp. strain RC607 MerA (mercuric reductase) and MerB (organomercurial lyase) were similar to those predicted from Staphylococcus aureus plasmid pI258 (67 and 73% amino acid identities, respectively); however, only 40% of the amino acid residues of RC607 MerA were identical to those of the mercuric reductase from gram-negative bacteria. A 69-kilodalton polypeptide was isolated and identified as the merA gene product by examination of its amino-terminal sequence.

Amino Acid Sequence↗
PubMed1987

Cloning and expression in Escherichia coli of chromosomal mercury resistance genes from a Bacillus sp.

A 7.9-kilobase (kb) chromosomal fragment was cloned from a mercury-resistant Bacillus sp. In Escherichia coli, in the presence of a second plasmid carrying functional transport genes, resistance to HgCl2 and to phenylmercury acetate (PMA) was expressed. Shortening the cloned fragment to 3.8 kb abolished resistance to PMA but not to HgCl2. In Bacillus subtilis, the 3.8-kb fragment produced mercuric reductase constitutively but did not produce resistance to HgCl2 or to PMA.

Bacillus↗
PubMed1986

Cadmium- and mercury-resistant Bacillus strains from a salt marsh and from Boston Harbor.

Bacteria resistant to cadmium or mercury or both were isolated from the Great Sippewissett Marsh (Cape Cod, Mass.) and from Boston Harbor. Many of these metal-resistant isolates were gram-positive aerobic sporeformers, although not necessarily isolated as spores. Although several of the isolated strains bore plasmids, cadmium and mercury resistances appeared to be, for the most part, chromosomally encoded. DNA sequence homology of the gram-positive cadmium- and mercury-resistant isolates was not demonstrable with metal resistance genes from plasmids of either gram-positive (pI258) or gram-negative (pDB7) origin. Cadmium resistance of all the marsh isolates tested resulted from reduced Cd2+ transport. On the other hand, three cadmium-resistant harbor isolates displayed considerable influx but no efflux of Cd2+. Hg-resistant strains detoxified mercury by transforming Hg2+ to volatile Hg0 via mercuric reductase.

Bacillus↗
PubMed1985

Transcriptional control of synthesis of acid-soluble proteins in sporulating Bacillus subtilis.

The major acid-soluble spore proteins (ASSPs) isolated from mature spores of Bacillus subtilis are designated alpha, beta, and gamma (about 60, 60, and 100 amino acids in length, respectively). Alpha and beta are very similar, and gamma is very similar to a less predominant ASSP called delta (about 115 amino acids). A minor and very basic ASSP called epsilon is the same size as alpha and beta but is unrelated antigenically. These and several minor ASSPs comprise at least three related families of sporulation-specific gene products. Expression of the alpha and beta genes, detectable as functional mRNA in vitro, coincides with the time of synthesis of all of the major ASSPs in vivo. This apparently coordinate expression is dependent on at least the spo0A, spoIIA, and spoIIIA loci, but not on the spoIVA or spoVA loci, consistent with the late stage of this expression (initiating at 3.5 h after the start of sporulation and peaking at 5 h after start of sporulation). A few minor ASSPs may be asynchronously expressed.

Bacillus subtilis↗
PubMed1984

Cloning the Bacillus subtilis 168 aroC gene encoding dehydroquinase.

An approx. 14-kb Sau3A fragment of Bacillus subtilis DNA containing the aroC and ser-22 genes has been isolated. Gene aroC is expressed in both B. subtilis and Escherichia coli and appears to contain its own promoter, allowing complementation in B. subtilis. However, expression in E. coli is dependent on insert orientation, so the direction of transcription can be deduced. The level of dehydroquinase-specific activity, encoded by the cloned aroC gene, is raised 30- to 40-fold in both E. coli and B. subtilis. The clones are stable in both E. coli and B. subtilis but appear to have undergone several large deletions during their construction.

Bacillus subtilis↗
PubMed1984

Cloning of an unstable spoIIA-tyrA fragment from Bacillus subtilis.

A recombinant cosmid clone was isolated from a library created from cosmid pQB79-1 and Bacillus subtilis DNA, and a 15 kb BamHI fragment derived from the cloned insert was transferred to the vector pHV33. The recombinant clone, pRC12, was capable of complementing eight auxotrophic markers in the spoIIA-tyrA region of the B. subtilis chromosome (map positions 205-210). It also complemented eight of nine markers in the spoIIA locus. The exception, spoIIA176, is the most distal marker from lysine. Although pRC12 failed to complement sporulation defects in spoVA or spoIVA (spoIIA+) strains, subclones of pRC12, lacking a functional spoIIA gene, did complement these mutations. pRC12 inhibited sporulation in a spo+ recE strain, possibly due to the presence of multiple functional spoIIA genes. Both the original cosmid and pRC12 were unstable in Escherichia coli and B. subtilis. Antibiotic selection of the vector resulted in extensive deletion of the insert, while selection for insert function in B. subtilis invariably led to loss of the chloramphenicol resistance vector function.

Bacillus subtilis↗
PubMed1975

Enzymatic repair of UV-irradiated DNA in vitro.

Excision repair of UV-damaged Bacillus subtilis transforming DNA has been carried out by a sequential enzyme system in vitro. Incision adjacent to the pyrimidine dimer in the DNA strand by correndonuclease II-initiated excision of the damage by the 5' in equilibrium 3'-directed exonuclease of the Micrococcus luteus DNA polymerase. Reinsertion of nucleotides into the gap in the strand by the DNA polymerase at 10 degrees C terminated in a single-strand break which was sealed by a polynucleotide ligase, thereby repairing the DNA strand. This restored biological activity to damaged DNA up to doses resulting in 60% inactivation of transforming activity. At higher doses, less repair was achieved, due to the development of double-strand breaks during the in vitro incision and excision steps.

Bacillus subtilis↗