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At least 19 recordsLinked to original sources
PubMed2026

Concurrence of antibiotic resistance genes in plasmid genomes shape environmental resistomes.

Horizontal transfer of plasmid-associated antibiotic resistance genes (ARGs) plays a pivotal role in environmental antibiotic resistance dissemination. Here, we characterized ARG concurrence patterns in plasmid genomes and examined plasmid-associated ARGs across 106 environmental metagenomes. Approximately half of known ARG subtypes (257) occurred in plasmid genomes, and nearly one-quarter of plasmids carried ARGs, including "super plasmids" harboring over 20 ARG subtypes spanning 10 antibiotic categories. Aminoglycoside resistance genes (AmRGs) exhibited the highest concurrence frequency (CF) with other ARGs in plasmid genomes, followed by beta-lactam and sulfonamide resistance genes. Many high-risk ARGs preferentially coexisted with AmRGs (45.6% of total AmRGs CF). Environmental metagenomes revealed distinct plasmid-associated ARG profiles between polluted and relatively pristine environments, with significantly greater diversity and abundance under anthropogenic pollution. Five widespread ARG subtypes occurred across all environmental media, whereas polluted environments contained more unique ARGs. Co-occurrence networks identified AmRGs as "hubs" linking multiple ARG subtypes in environmental resistomes. Plasmid-ARG interaction networks further showed more complex potential plasmid-mediated concurrent dissemination in polluted environments. Collectively, use of aminoglycosides is more likely to cause co-transmission of multiple plasmid-related ARGs than other antibiotics, and CF of ARGs is proposed as an important supplementary factor for evaluating ARG dissemination under anthropogenic antibiotic stress.

Antibiotic resistance genes (ARGs)↗
PubMed1975

Cloning, isolation, and characterization of replication regions of complex plasmid genomes.

EcoRI endonuclease-generated DNA fragments carrying replication regions of the F'lac and R6-5 plasmids have been cloned and isolated, using as a selection vehicle a nonreplicating ampicillin-resistance DNA fragment derived from a Staphylococcus aureus plasmid. Heteroduplex analysis of the constructed plasmid chimeras and the parent replicons has localized the cloned R6-5 replication region to a DNA segment between kilobase pair coordinates 1.0 and 88.0 on the R6-5 map. Physical proximity between the plasmid replication functions and the locus governing plasmid incompatibility has been shown for both parent replicons. The cloning method reported appears to be generally applicable for the identification and isolation of replication regions of a variety of complex genomes.

Centrifugation, Density Gradient↗
PubMed1975

In vitro construction of different oligomeric forms of lambdadv DNA and studies of their transforming activities.

Plasmid lambdadv1, which is in a dimeric form, was converted to a linear monomer duplex by the action of EcoRI restriction endonuclease that incises at a unique site in this plasmid genome. The resulting products were then joined by Escherichia coli DNA ligase to produce molecules with various oligomeric forms, and from these monomeric, dimeric, or trimeric circular molecules were purified. By transformation of cells with these DNAs, clones were obtained that carried lambdadv1 in a monomeric or dimeric form. The former type of clones have not been generated in vivo, except for one in a different host strain, and carriers of timeric or tetrameric lambdadv1's have not been obtained so far. It was observed that a considerable fraction of these oligomeric circular DNAs were converted to lower oligomers (e.g., from trimer to dimer) during transformation. The characteristics of the monomeric lambdadv1 carriers obtained were compared with those of dimeric lambdadv1 carriers. The stabilities of the plasmids of the two forms were the same. However, the monomeric plasmid carriers were less tolerant to lambdavir phage infection and perpetuated about 30% less plasmid genomes in monomer units. Furthermore, dimeric plasmid carriers appeared spontaneously and accumulated in cultures of the monomeric lambdadv1 carriers.

Coliphages↗
PubMed1976

Mutants of the killer plasmid of Saccharomyces cerevisiae dependent on chromosomal diploidy for expression and maintenance.

Mutants of the killer plasmid of Saccharomyces cerevisiae have been isolated that depend upon chromosomal diploidy for the expression of plasmid functions and for replication or maintenance of the plasmid itself. These mutants are not defective in any chromosomal gene needed for expression or replication of the killer plasmid.--Haploids carrying these mutant plasmids (called d for diploid-depen;ent) are either unable to kill or unable to resist being killed or both and show frequent loss of the plasmid. The wild-type phenotype (K+R+) is restored by mating the d plasmid-carrying strain with either (a) a wild-type sensitive strain which apparently has no killer plasmid; (b) a strain which has been cured of the killer plasmid by growth at elevated temperature; (c) a strain which has been cured of the plasmid by growth in the presence of cycloheximide; (d) a strain which has lost the plasmid because it carries a mutation in a chromosomal mak gene; or (e) a strain of the opposite mating type which carries the same d plasmid and has the same defective phenotype, indicating that the restoration of the normal phenotype is not due to recombination between plasmid genomes or complementation of plasmid or chromosomal genes.--Sporulation of the phenotypically K+R+ diploids formed in matings between d and wild-type nonkiller strains yields tetrads, all four of whose haploid spores are defective for killing or resistance or maintenance of the plasmid or a combination of these. Every defective phenotype may be found among the segregants of a single diploid clone carrying a d plasmid. These defective segregants resume the normal killer phenotype in the diploids formed when a second round of mating is performed, and the segregants from a second round of meiosis and sporulation are again defective.

Crosses, Genetic↗
PubMed1975

Synthesis of E colicins in Escherichia coli.

Mitomycin C treatment of Escherichia coli cells containing one of the ColE plasmids results in specific inhibition of chromosomal protein synthesis and a high rate of protein synthesis from about 35% of the plasmid genome, whereas similar treatment of plasmid-free cells has no measureable effect on protein synthesis. In the case of ColE2- and ColE3-containing cells, the antibiotic colicin protein (molecular weight about 78000) and two others (molecular weight about 11000 and 6000) are coordinately synthesized in the approximate molar ratio 1:4:1, while in ColE1-containing cells only the colicin protein is synthesized in large amounts. Partially purified colicin E2 isolated from the outer cell surface is associated with the two small proteins in the approximate molar ratio 1:1:1, indicating that not are they only synthesized coordinately but are released as a ternary complex.

Cell Survival↗
PubMed1976

Cell wall lipopolysaccharide response to the ColIb plasmid mutants.

Mutants of ColIb plasmid affected the synthesis of O-side chains of lipopolysaccharides (LPS) in Salmonella. The plasmid srd 25 (defective in colicin synthesis) caused a significant decline of rhamnose and mannose content and lack of abequose in LPS of S. typhimurium. The number of repeating units in O-side chains was decreased after the indroduction of srd 25. Cultures of S. typhimurium and S. enteritidis harboring drd2 (derepressed in colicin production) polymerised dideoxyhexose-defective O-side chains i.e. deprived of abequose and tyvelose, respectively. In dideoxyhexoseless S. meleagridis the content of rhamnose and mannose were reduced. The information for the alterations of Salmonella LPS was contained in the plasmid genome. In the wild-type plasmids the genes controlling the O-antigen changes were not expressed.

Cell Wall↗
PubMed1978

Cloning and characterization of EcoRI and HindIII restriction endonuclease-generated fragments of antibiotic resistance plasmids R6-5 and R6.

DNA fragments generated by the EcoRI of HindIII endonucleases from the low copy number antibiotic resistance plasmids R6 and R6-5 were separately cloned using the high copy number ColE1 or pML21 plasmid vectors and the insertional inactivation procedure. The hybrid plasmids that were obtained were used to determine the location of the EcoRI and HindIII cleavage sites on the parent plasmid genomes by means of electron microscope heteroduplex analysis and agarose gel electrophoresis. Ultracentrifugation of the cloned fragments in caesium chloride gradients localized the high buoyant density regions of R6-5 to fragments that carry the genes for resistance to streptomycin-spectinomycin, sulfonamide, and mercury and a low buoyant density region to fragments that carry the tetracycline resistance determinant. Functional analysis of hybrid plasmids localized a number of plasmid properties such as resistances to antibiotics and mercury and several replication functions to specific regions of the R6-5 genome. Precise localisation of the genes for resistance to chloramphenicol, kanamycin, fusidic acid and tetracycline was possible due to the presence of identified restriction endonuclease cleavage sites within these determinants. Only one region competent for autonomous replication was identified on the R6-5 plasmid genome and this was localized to EcoRI fragment 2 and HindIII fragment 1. However, two additional regions of replication activity designated RepB and RepC, themselves incapable of autonomous replication but capable supporting replication of a linked ColE1 plasmid in polA- bacteria, were also identified.

Bacteriocin Plasmids↗
PubMed1975

Site specific recA--independent recombination between bacterial plasmids: involvement of palindromes at the recombinational loci.

A recA-independent recombinational event is described which results in insertion of an entire plasmid genome at a unique site of another plasmid, and coincident excision of a precisely defined DNA segment originally present at the point of the insertion. The resulting recombinant molecules subsequently can undergo site-specific translocation of their component segments or inversion of their original DNA sequence orientation. The events observed entail nonreciprocal exchange of genetic material, and involve a discrete nucleotide sequences that is duplicated in rotationally symmetrical reverse orientation on plasmid DNA (i.e., inverted repeat; palindrome).

Base Sequence↗
PubMed1978

In vitro construction of deletion mutants of the bacteriocinogenic plasmid Clo DF13.

The isolation and characterization of deletion mutants of the bacteriocinogenic plasmid Clo DF13 is described. To construct these deletion mutants, DNA of Clo DF13::Tn901 and Clo DF13-rep3::Tn901 plasmids was digested with restriction endonucleases, ligated with T4 ligase and introduced by transformation into Escherichia coli. The presence of the ampicilline transposon Tn901 facilitated the selection of plasmids. The resulting Clo DF13::Tn901 deletion mutants were analyzed by digestion with restriction endonucleases and electron microscopy. From the properties of the various deletion mutants it was concluded that a Clo DF13 DNA region, extending from 5 to 11.5% on the physical map, is essential for the replication of Clo DF13. This region, comprising about 600 base pairs, contains in addition to an origin of replication, DNA sequences which are involved in the regulation of Clo DF13 DNA replication. Furthermore it was observed that in case of the Clo DF13 copy mutant, Clo DF13-rep3, deletion of the 43% to 63% part of the plasmid genome, resulted in the generation of multimeric plasmid structures, accompanied with an impaired segregation of the plasmids to daughter cells.

Bacteriocins↗
PubMed1978

Isolation and characterization of a Clo DF13::Tn901 plasmid mutant with thermosensitive control of DNA replication.

After nitrosoguanidine mutagenesis, a mutant Escherichia coli strain harboring the Clo DF13::Tn901 plasmid pJN03 was isolated that is thermosensitive (Ts) for growth at 43 degrees C. The mutation responsible for this thermosensitive phenotype resides on the pJN03 plasmid genome. Cells harboring the pJN03 cop-1(Ts) plasmid mutant showed a large increase in plasmid copy number at 43 degrees C accompanied by an increase in the synthesis of plasmid-specified gene products like cloacin DF13 and beta-lactamase. The pJN03 cop-1(Ts) mutant showed uncontrolled plasmid DNA replication at the nonpermissive temperature. Analysis of plasmid deletions showed that the mutation is located in the Clo DF13 map interval from 0 to 12% or 29 to 45%. This implies that native cloacin DF13 and the Clo DF13-specified polypeptides B, C, D, E, and G are not involved in the pleiotropic phenotype of the plasmid mutant pJN03 cop-1(Ts).

Bacteriocins↗
PubMed2025

Diversity and distribution of the lanthanome in aerobic methane-oxidising bacteria.

BACKGROUND: Lanthanides (Ln) play important and often regulatory roles in the metabolism of methylotrophs, including methanotrophs, particularly through their involvement in methanol oxidation. However, the diversity, distribution, and ecological relevance of Ln-associated proteins (the lanthanome) in aerobic methane-oxidising bacteria (MOB) remain underexplored. This study investigates the lanthanome using genome, plasmid, and proteome data, alongside metatranscriptome data from methane-rich lake sediments. RESULTS: We surveyed 179 genomes spanning Proteobacterial, Verrucomicrobial, and Actinobacterial MOBs to examine the distribution of Ln-dependent methanol dehydrogenases (MDHs) and Ln transport proteins. Distinct lineage-specific patterns were observed: XoxF5 was the most widespread MDH variant in Proteobacteria, while XoxF2 was restricted to Verrucomicrobia. Transporter systems also showed distinct patterns, with LanM restricted to Alphaproteobacteria, LanPepSY and LanA confined to Gammaproteobacteria, and LutH-like receptors broadly distributed across all lineages. Homologues of these genes were also detected on plasmids, indicating potential for horizontal gene transfer. In Lake Washington sediment metatranscriptomes, lanthanome transcripts were detected, with Proteobacteria as dominant contributors. Notably, a large fraction of xoxF transcripts were affiliated with non-MOB Methylophilaceae, consistent with known cooperative interactions with MOB. Using Methylosinus trichosporium OB3b as a model, we assessed methane oxidation and proteomic responses to soluble CeCl3 and a mixed-lanthanide ore. Lag phases were prolonged in the presence of lanthanides, particularly with ore, but methane oxidation rates converged across treatments after acclimation. Proteomic analysis revealed extensive condition-specific responses, with 724 proteins differentially expressed in Ore treatment compared to 60 under CeCl3. XoxF3 and XoxF5 were upregulated while MxaF and its accessory proteins were downregulated, consistent with the "lanthanide switch". Notably, LanM was not expressed despite being encoded, whereas LutH-like receptor was downregulated under both treatments, likely reflecting regulatory control to prevent excess metal uptake. Additional upregulation of a TonB-dependent receptor and ABC transporter suggests a potential lanthanophore-mediated uptake strategy. CONCLUSION: This study highlights the diversity and ecological activity of Ln-binding and transport systems in MOBs, their plasmid localisation and potential mobility, and their distinct regulation under different Ln sources. The strong proteomic response to complex ore underscores the physiological flexibility of MOBs in coping with natural lanthanide forms. These findings provide a framework for ecological studies and candidate targets for biotechnological applications in methane bioconversion and sustainable lanthanide recovery from complex materials.

Horizontal gene transfer↗
PubMed1978

Transduction of plasmid determinants in Staphylococcus aureus and Escherichia coli.

Buoyant density analysis of transducing lysates derived from Staphylococcus aureus and Escherichia coli indicated that phage particles bearing plasmid determinants contain a quantity of DNA equivalent to that found in the lytic particles. Transducing particles that bear plasmid determinants smaller than viral DNA must therefore contain a quantity of DNA in excess of a single plasmid genome. In the E. coli P1vir system, a dependence upon host-mediated recombination for the transduction of small plasmids, but not for large R factors or chromosomal genes, was observed. However, no evidence for the involvement of such functions in the transduction of S. aureus plasmids was obtained. Although the origin of the additional DNA in plasmid transducing particles has not been identified, circumstantial evidence has been presented in the staphylococcal system indicating that transducing particles carrying a small tetracycline plasmid are not formed by the wrapping of multiple copies of this plasmid DNA.

Chromosomes, Bacterial↗
PubMed1977

On the mechanism of genetic recombination: the maturation of recombination intermediates.

DNA molecules of the plasmid ColEl are normally recovered from wild-type cells as a set of monomer- and multimer-size rings. The data of this paper show that the multimer-size species are a product of genetic recombination. Multimer rings do not arise after transfection of purified monomers into bacterial host cells lacking a functional recA recombination system. Analogously, purified dimers, trimers, and tetramers, transfected into recA- cells, can replicate, but are constrained to remain in those conformations. Only upon transfection into rec+ cells can they regenerate the full spectrum of monomer- and multimer-size species. In this paper we trace the flow of genetic information from the monomer to the multimer state and back again under the guidance of the recA recombination system. The formation of multimer-size DNA rings is discussed as a natural consequence of the maturation of a Holliday recombination intermediate formed between two monomer plasmid genomes.

Chromosomes↗
PubMed1979

[Analysis of merodiploid strains of Sh. flexneri that have lost virulence].

Episome F'13 introduced into the genome of a virulent Sh. flexneri strain brought about changes in a number of properties of the recipient strain. The expression of these properties was not connected with the chromosome area allelic to the plasmid genome. These changes seem to be induced by the mobilization of the chromosome genes of E. coli. The loss of virulence in Sh. flexneri strains carrying episome F'13 seemed to be the consequence of two reasons: the overlapping of kcpA gene by its dominant avirulent allele and abnormal synthesis of cell wall lipopolysaccharide due to the transfer of the mobilized genes from the donor strain F'13. When the preliminary mapping of genes on the chromomome was made with the use of plasmids, it was found necessary to use F-episomes which had no influence on the changes occurring in the phenotypic characteristics of the recipient.

Alleles↗
PubMed1977

Mutations of temperature sensitivity in R plasmid pSC101.

Temperature-sensitive (Ts) mutant plasmids isolated from tetracycline resistance R plasmid pSC101 were investigated for their segregation kinetics and deoxyribonucleic acid (DNA) replication. The results fit well with the hypothesis that multiple copies of a plasmid are distributed to daughter cells in a random fashion and are thus diluted out when a new round of plasmid DNA replication is blocked. When cells harboring type I mutant plasmids were grown at 43 degrees C in the absence of tetracycline, antibiotic-sensitive cells were segregated after a certain lag time. This lag most likely corresponds to a dilution of plasmids existing prior to the temperature shift. The synthesis of plasmid DNA in cells harboring type I mutant plasmids was almost completely blocked at 43 degrees C. It seems that these plasmids have mutations in the gene(s) necessary for plasmid DNA replication. Cells haboring a type II mutant plasmid exhibited neither segregation due to antibiotic sensitivity nor inhibition of plasmid DNA replication throughout cultivation at high temperature. It is likely that the type II mutant plasmid has a temperature-sensitive mutation in the tetracycline resistance gene. Antibiotic-sensitive cells haboring type III mutant plasmids appeared at high frequency after a certain lag time, and the plasmid DNA synthesis was partially suppressed at the nonpermissive temperature. They exhibited also a pleiotrophic phenotype, such as an increase of drug resistance level at 30 degrees C and a decrease in the number of plasmid genomes in a cell.

DNA, Bacterial↗
PubMed1979

[Transposition of the deo operon structural genes in Escherichia coli K-12 to plasmid RP4 using bacteriophage mu].

Transposition of the structural genes of the deo operon of Escherichia coli K-12 into plasmid RP4 by means of temperate bacteriophage Mu was carried out. Some variants of composite RP4-deo-Mu plasmids were obtained and the expression of the deo genes integrated into the RP4 plasmid genome was studied. It was shown that the expression of these genes remains under the control of the chromosomal regulatory genes (deoR and cytR); although the activity of thymidine phosphorilase in the strain E. coli which contains hybrid plasmid is 4-6 fold greater than that in strains of E. coli with chromosomal localization of the deo operon.

Bacteriophage mu↗