Transfer Of Chromosomal Markers Research Articles

Conjugal transfer of plasmid and chromosomal markers between strains of Thiobacillus versutus

In experiments on conjugation in Thiobacillus versutus with the use of pTAV1-less strains as recipients, we have proved that the derivative of the wild-type T. versutus cryptic plasmid pTAV1 (107 kb) marked with Tn1721 (Tcr) transposon demonstrates Tra- phenotype but can be mobilized for transfer by pSa Tra+ broad-host-range helper plasmid at a low frequency. The possibility of chromosomal gene exchange between different auxotrophic and drug-resistant T. versutus mutants has been confirmed. The previously assumed participation of plasmid pTAV1 in the above process must be excluded because conjugal transfer of chromosomal markers can be observed even when two pTAV1-free strains are mated. Formation of some classes of transconjugants can be reasonably explained only when two-directional chromosomal DNA transfer (retrotransfer) is considered. At this stage of our studies we can not propose any hypothesis on the mechanism of chromosomal gene transfer. The possible role of the megaplasmids discovered in T. versutus in chromosome mobilization needs to be elucidated.

Conjugal retrotransfer of chromosomal markers inAzotobacter vinelandii

The IncP plasmids R68.45 and pJB3JI mediate retrotransfer (i.e., transfer of chromosomal markers from the recipient bacterium to the original donor) in homologous matings withAzotobacter vinelandii. Retrotransfer is not an early event inAzotobacter. On the contrary, it begins after genetic transfer in the usual direction, i.e., from the donor bacterium to the recipient, has been taking place for some time. Transfer of chromosomal markers mediated by the RP4/Tn5-Mob system does not undergo retrotransfer. The simplest hypothesis compatible with our results is that IncP plasmids that confer a high chromosome-mobilizing ability promote retrotransfer when transferred to the recipient bacteria.

Mapping of pgi and gpd genes involved in C-1 assimilation in the obligate methylotroph Methylobacillus flagellatum

Homologous matings with plasmids R68.45 and pULB113, and also with Hfr type donor were employed for mapping pgi and gpd genes involved in C-1 metabolism in the obligate methylotroph Methylobacillus flagellatum. A preliminary map of the late chromosomal region was constructed on the basis of these experimental results. The C-1 markers were linked to methionine and leucine auxotrophy and nalidixic acid resistance markers. The phenomenon of retrotransfer, or shuttle transfer of chromosomal markers by Inc P1 plasmids, revealed earlier, was demonstrated for M. flagellatum.

Shuttle transfer (or retrotransfer) of chromosomal markers mediated by plasmid pULB113.

The IncP1 plasmid pULB113 (RP4::miniMu) not only mediates the transfer of chromosomal markers in the classical direction (i.e. from the donor to the recipient cell) but also in the opposite direction (i.e. from the recipient bacterium to the donor). This phenomenon of retrotransfer was observed in homologous matings with Pseudomonas fluorescens, Alcaligenes eutrophus and Salmonella typhimurium. Retrotransconjugants could be discriminated from direct transconjugants by appropriate chromosomal and plasmid markers used to distinguish the mating partners not bearing pULB113. Retrotransfer of chromosomal markers occurred at frequencies equal to, or sometimes greater than, those observed for the direct mobilization, thus allowing the recovery of "recipient" recessive markers in the "donor" with linkage values similar to those found in the normal direction. Retrotransfer was also observed in heterospecific matings involving A. eutrophus and pULB113 bearing P. fluorescens: R-primes carrying different selected and unselected markers were recovered in both bacteria. "Retrotransfer" or "shuttle transfer" seems to be a specific trait of IncP1 plasmids.

Use of plasmid pULB113 (RP4::Mini-Mu) to construct a genomic map ofAeromonas hydrophila

Plasmid pULB113 (RP4::Mini-Mu) promoted homologous gene transfer in Aeromonas hydrophila; transfer of chromosomal markers occurred at frequencies of between 10-3 and 10-4 per donor cell regardless of the marker selected; this indicated chromosome transfer from multiple origins. With a variety of amino acid biosynthetic markers, a single circular map of this bacterium was constructed.

Plasmid replication and Hfr formation in strains ofEscherichia coli carryingseg mutations

Several conditional-lethal mutantions that do not permit the replication of F-factors of Escherichia coli K-12 are located at a site called seg. This gene is located on the E. coli chromosome between ser B and thr. It is unrelated to other known genes involved in DNA replication. Strains carrying seg mutations were unable to replicate F'-lac+, several F'-gal+s, F'-his+ and bacteriophage gamma at 42 degrees. However, neither phage T4, ColE1, nor any of the R factors tested were prevented from replicating at 42 degrees C. When the kinetics of the loss of F-primes is studied in seg strains, it is found that the rate of curing depends on the size of the plasmid, larger F factors curing faster than smaller ones, and that Hfrs are formed at high frequencies. The Hfrs showed both F-genote enlargement and normal transfer of chromosomal markers. The F-genotes are unstable and segregate chromosomal markers at high frequencies. Some orthodox Hfrs were examined, and two that were known to revert to the F+ condition relatively frequently were found to generate enlarged F-genotes on mating, whereas two strains that were very stable with respect to the F+ state did not show F-genote formation. F-genote formation from seg Hfr stains is dependent on a functional recA gene, as F-genote formation was not seen with a seg-2, recA-1 Hfr. This is in contrast to F-genote enlargement shown by both orthodox Hfrs and an Hfr strain constructed by integration of a temperature-sensitive F'-gal+, whose F-genote enlargement is Rec-independent. Thus there may be more than one mechanism for the formation of enlarged F-genotes.

Citrobacter freundii Mutants Deficient in Host Specificity Functions and Their Recipient Ability for Foreign Deoxyribonucleic Acid

Summary: The isolation and properties of mutants of Citrobacter freundii deficient in host specificity functions is described. Two mutant types have been isolated, one deficient in restriction (hsr) and another one deficient in both restriction and modification (hss). These non-restricting mutants are good recipients for plasmid DNA in conjugation experiments with Escherichia coli donor strains. Transfer of chromosomal markers was observed in crosses between E. coli Hfr strains and non-restricting mutants of C. freundii, and in crosses between Salmonella typhimurium Hfr or S. abony Hfr strains and non-restricting C. freundii recipients. Recombinants from these crosses are unstable, partially diploid strains.

Episome-carried surface antigen K88 of Escherichia coli. I. Transmission of the determinant of the K88 antigen and influence on the transfer of chromosomal markers.

Ørskov, Ida (Statens Seruminstitut, Copenhagen, Denmark), and Frits Ørskov. Episome-carried surface antigen K88 of Escherichia coli. I. Transmission of the determinant of the K88 antigen and influence on the transfer of chromosomal markers. J. Bacteriol. 91:69-75. 1966.-The transmission of the determinant of the Escherichia coli K88 antigen in mixed cultures of E. coli strains is described. The K88 factor could not be transferred by filtrates, nor could responsible phages or colicines be detected. Acriflavine was shown to "cure" the bacteria for the K88 antigen. Generally, the strains having acquired the K88 antigen also acquired the ability to transfer chromosomal markers, but this ability was in some cases retained by segregants which had lost the K88 antigen. Introduction into an F(+) strain caused reduction of the recombination frequency and disappearance of the f(+) antigen. Not all wild-type strains with the K88 antigen are genetic donors of this antigen, at least not to a discernible degree. It was concluded that the K88 antigen determinant is carried by an episome.

Chromosome transfer and the DNA replication cycle in [formula omitted], [formula omitted

Phenethyl alcohol (PEA) has been employed as an inhibitor of DNA synthesis in order to elucidate the relationship between the synthesis of DNA in Hfr strains of Escherichia , coli and the transfer of chromosomal markers during conjugation ( Bouck and Adelberg, 1963; and Jacob, Brenner, and Cuzin, 1963). Treick and Konetzka (1964) have shown recently that PEA inhibits the initiation of new cycles of DNA replication in E . coli but permits the completion of those cycles initiated before addition of PEA to the medium. Therefore, cycles of DNA replication can be controlled by the addition, removal, and readdition of PEA to a culture at specific time intervals. The relationship of the DNA replication cycle to the ability of the Hfr to transfer chromosomal markers constitutes the subject of this investigation.

GENE TRANSFER BY F' STRAINS OF ESCHERICHIA COLI K-12. I. DELAY IN INITIATION OF CHROMOSOME TRANSFER.

Pittard, James (Yale University, New Haven, Conn.), John S. Loutit, and Edward A. Adelberg. Gene transfer by F' strains of Escherichia coli K-12. I. Delay in initiation of chromosome transfer. J. Bacteriol. 85:1394-1401. 1963.-Two different F' strains were found to transfer both F-merogenote and chromosomal markers to recipient strains. When zygotes having received different chromosomal markers from the male were selected, a high percentage of them were found to have also received F-merogenote markers under conditions in which the mating of more than one male cell with a single female cell was excluded. An analysis of the kinetics of zygote formation revealed that chromosomal markers began to be transferred from F' strains 8 to 10 min later than from their analogous Hfr strains. The rate of chromosome transfer is the same from both F' and Hfr strains, and the difference observed in kinetic experiments was shown not to be due to any difference between the sequence of chromosomal genes in the F' and Hfr strains. F' strains and Hfr strains showed no difference in ability to form specific pairs with female recipients shortly after mixing. The observed delay in the transfer of chromosomal markers from F' cells thus means that, after specific pair formation, F' cells take 8 to 10 min longer than Hfr cells to initiate chromosome transfer.