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At least 757 records · Page 42Linked to original sources
PubMed1971

Early intermediate state of transforming deoxyribonucleic acid during uptake by Bacillus subtilis.

Examination of the effects of ethylenediaminetetraacetic acid (EDTA) on uptake of transforming deoxyribonucleic acid (DNA) by Bacillus subtilis allowed definition of a new intermediate state of transforming DNA during uptake. Markers in this state, termed "EDTA-resistant," are bound to the cell, are sensitive to inactivation by deoxyribonuclease, but may become deoxyribonuclease-resistant despite the addition of excess EDTA. Markers become EDTA-resistant quadratically with time after the addition of DNA to a competent culture, but linearly after exposure of competent cells to a brief pulse of DNA. An attractive model consistent with these findings is that EDTA blocks only the initiation of entry of a molecule of DNA.

Bacillus subtilis↗
PubMed2005

Metagenomics for studying unculturable microorganisms: cutting the Gordian knot.

More than 99% of prokaryotes in the environment cannot be cultured in the laboratory, a phenomenon that limits our understanding of microbial physiology, genetics, and community ecology. One way around this problem is metagenomics, the culture-independent cloning and analysis of microbial DNA extracted directly from an environmental sample. Recent advances in shotgun sequencing and computational methods for genome assembly have advanced the field of metagenomics to provide glimpses into the life of uncultured microorganisms.

Genetics, Microbial↗
PubMed1974

Genetic recombination in Rhodopseudomonas capsulata.

A system for genetic exchange in Rhodopseudomonas capsulata has been discovered. Each genetic marker thus far examined can be transferred, and many strains of Rps. capsulata can participate in genetic exchange. The mechanism of gene transfer seems unlike that of any previously described bacterial system, since genes can be transferred by cell-free filtrates, but the vector is resistant to deoxyribonuclease and has a sedimentation constant of about 70 S.

Cell-Free System↗
PubMed1970

Molecular recombination between R-factor deoxyribonucleic acid molecules in Escherichia coli host cells.

THREE PREVIOUSLY STUDIED R FACTORS WERE USED: 222/R4, controlling transmissible resistance to sulfonamide, streptomycin, chloromycetin, and tetracycline (SU(r) SM(r) CM(r) TC(r)); 222/R3, a derivative of 222/R4 (now termed 222/R3W) having lost TC(r); and R15, controlling infectious resistance to SU and SM only. Two types of derivative R factors were isolated from 222/R4 by serial subculture in Salmonella species. One derivative, termed 222/R1, lost resistance to SU, SM, and CM, and the other, termed 222/R3N, lost only TC(r). Each factor was transferred to a standard Escherichia coli K-12 host. Recombinant factors of 222/R4 phenotype were isolated by selection after mixed culture of E. coli (222/R1)(+) and (222/R3N)(+) strains. Density-gradient equilibrium centrifugation of lysates of E. coli R(+) hosts in the presence of ethidium bromide separated R-factor deoxyribonucleic acid (DNA) as a heavy satellite peak which was subjected to electron microscopy or analytical density gradient centrifugation. Each DNA comprised a unimolecular species of circular DNA. The contour of R15 measured 22.3 mum [equivalent to 46 x 10(6) atomic mass units (AMU)], and that of 222/R4 measured 33.6 mum (70 x 10(6) AMU). 222/R3W appeared to be a point mutant or small deletion of 222/R4 with an almost identical size, whereas 222/R3N had lost a DNA segment of about 3 mum, and measured 30.3 mum or 63 x 10(6) AMU. The 222/R1 factors also appeared to have arisen by loss of DNA from 222/R4, 222/R1A being 22.3 mum or 46 x 10(6) AMU, whereas all other 222/R1 factors appeared to be duplicates, measuring 25.6 mum or 53 x 10(6) AMU. The DNA from six recombinant factors of R4 phenotype was indistinguishable in size and configuration from the parental 222/R4. In most cases, the number of R-factor copies (present as covalently closed circular molecules) per copy of the E. coli chromosome was less than 2, ranging from 1.2 to 3.3.

Centrifugation, Density Gradient↗
PubMed1971

ColB2-K77, a fertility-repressed F-like factor.

The colicinogenic B factor, transferred from Escherichia coli strain K77 (and termed ColB2-K77 or ColB2) to an E. coli K12 F(-) strain, is capable of promoting its own transfer to other K12 F(-) strains at a low rate (from LFC cultures) which can be increased under special conditions (HFC cultures). LFC cultures of K12 (ColB2)(+) F(-) strains show a low level of adsorption of F-specific phage particles which also increases under HFC conditions. The ColB2 factor is thus inferred to be an F-like sex factor which is repressed in its fertility. This repression is concluded to be due to a cytoplasmic repressor since, when ColB2 is present in cells containing an F factor (either autonomous or integrated), F fertility is also repressed as shown by the inability of such (ColB2)(+)F(+) [or (ColB2)(+)Hfr] strains to plaque F-specific phages, and by a reduction in the level of chromosomal transfer from such strains, compared to the corresponding F(+) (or Hfr) control strains. Mutants of the ColB2 factor in which fertility is no longer repressed (fertility derepressed or Fdr mutants) have been isolated. The ColB2Fdr mutant strains do not appear to be able to mobilize chromosomal transfer, although they have acquired F-specific phage sensitivity demonstrable by plaque formation and they transfer their colicin factor at high frequency and are well piliated. The Fdr mutation is presumed to result in the inability to synthesize the cytoplasmic fertility repressor since the ColB2Fdr factor does not repress the fertility of an F factor when present in the same host strain. A fertility-repressed drug resistance factor of the R(f) type is not stable in the presence of a ColB2 factor in the same cell and is eliminated in about 10% of the cells per generation. In contrast, another factor characteristic of the R(i) type is fully compatible with ColB2. Under conditions artificially stabilizing (ColB2Fdr)(+) (Rf)(+) strains, the enhanced fertility of ColB2Fdr is not repressed by the presence of the R factor, nor does the presence of R(f) in the intermediate strain of an HFC (for ColB2) system inhibit the normal increase in ColB2 transmissibility. It is concluded that the repressors of R(f) and ColB2, although both active on F fertility, are different; this may indicate that at least two independently repressible cistrons are involved in the expression of fertility characteristics.

Adsorption↗
PubMed1971

Altered deoxyribonucleic acid polymerase activity in a methyl methanesulfonate-sensitive mutant of Bacillus subtilis.

Of six deoxyribonucleic acid repair mutants of Bacillus subtilis assayed for deoxyribonucleic acid polymerase, only the methyl methanesulfonate-sensitive and ultraviolet light-sensitive mutant JB1-49(59) has impaired polymerase activity. Extracts prepared by sonic treatment or gentle lysis had about 10% of the wild-type activity with poly d(A-T), an alternating copolymer of deoxyadenylate and deoxythymidylate, used as template. The sensitivity to methyl methanesulfonate and ultraviolet light and the low level of polymerase activity transformed and reverted together, indicating that the two characteristics are a pleiotropic manifestation of a single mutation. Mixed extract and kinetic experiments mitigated against an altered nuclease activity as the enzymatic consequence of the mutation. Also, the mutant and wild type activities were stimulated equally by Escherichia coli exonuclease III. The residual activity in the mutant showed several differences from the wild-type activity: it purified differently, was more sensitive to sulfhydryl reagents, and displayed a different template specificity. We tentatively conclude that either the mutation in JB1-49(59) has introduced a qualitative as well as a quantitative change in the polymerase or the wild type contains two distinct polymerases, one of which is missing in the mutant.

Adenine Nucleotides↗
PubMed2003

Transposon-based strategies for microbial functional genomics and proteomics.

Transposons are mobile genetic elements that can relocate from one genomic location to another. As well as modulating gene expression and contributing to genome plasticity and evolution, transposons are remarkably diverse molecular tools for both whole-genome and single-gene studies in bacteria, yeast, and other microorganisms. Efficient but simple in vitro transposition reactions now allow the mutational analysis of previously recalcitrant microorganisms. Transposon-based signature-tagged mutagenesis and genetic footprinting strategies have pinpointed essential genes and genes that are crucial for the infectivity of a variety of human and other pathogens. Individual proteins and protein complexes can be dissected by transposon-mediated scanning linker mutagenesis. These and other transposon-based approaches have reaffirmed the usefulness of these elements as simple yet highly effective mutagens for both functional genomic and proteomic studies of microorganisms.

Artificial Gene Fusion↗