Structural bases for f plasmid conjugation and f pilus. The f cell is a modified cell and may undergo conjugation with an f cell. Bacterial conjugation is the transfer of genetic material between bacterial cells by direct celltocell contact or by a bridgelike connection between two cells. Exam 4 bacterial genetics biology 3300 with stark at. Despite the discovery of conjugation by f plasmids in escherichia coli over seven decades ago, we have only now visualized the f encoded transfer channel and f pilusassociated platforms in the e. Bacterial conjugation experiment essay 934 words bartleby. Responsible for the earliest observation of genetic transfer 206, the f fertility factor of e. Shade in the appropriate plate areas below as an indication of growth.
F strains of escherichia coli a transfer the f factor to other strains at a high frequency. At present, more than 200 different f like plasmids with highly related dna transfer genes. The f factor is 100 kb of duplex dna with two replicationorigin regions figure 1. This discovery led to another discovery that she made soon after. The f factor is one of the most well studied conjugative plasmids plasmids are circular episomes and is the most well studied conjugative system. Conjugation between bacterial and mammalian cells nature. By agreement with the publisher, this book is accessible by the search feature, but cannot.
Temperaturesensitive conjugationdefective f factor in. In which of the following matings would chromosomal genes be transferred most frequently. Bacterial conjugation is the transfer of genetic material between bacterial cells by direct. They can move bacterial genes that give bacteria antibiotic resistance or. A mutant strain of escherichia coli k12 which is unable to transfer genetic material at 42 c has been isolated. Structure and function of the f factor and mechanism of conjugation. To explain the mechanisms of gene transfer in bacteria. F factor plasmid forms hfrs in salmonella typhimurium at many fewer sites and at a much lower frequency than in escherichia coli.
Perhaps the most wellstudied is the f pilus of escherichia coli, encoded by the f plasmid or fertility factor. Printed temperaturesensitive conjugationdefective f. Factors influencing the dissemination of dna by bacterial conjugation. After conjugation, bacteria will carry both plasmid 1 and plasmid 2. Also dna may be transferred from one bacterium to another via an hfr high frequency of recombination strain, in which an f plasmid has integrated into the chromosome and begins transfer of dna from that chromosomal location.
Bacterial genetics flashcards by john mcclatchy brainscape. Based upon the way hfrs are formed, what would be a simple explanation for this difference between s. This strain and its derivatives also show an altered sensitivity to certain ribonucleic acidcontaining male specific phages at 42 c. After conjugation, each cell involved has a copy of the shared dna. The f factor carries an operon of about 30 genes, encoding tra proteins promoting transfer figure 1. The conjugal systems of the broadhostrange plasmid rp4 and its relatives as well as the grampositive conjugation system tn916.
During excision, the a and e regions of the chromosome are retained in the f factor. The f sex factor of escherichia coli is a paradigm for bacterial conjugation and its transfer tra region represents a subset of the type iv secretion system t4ss family. Although often incorrectly characterized as the bacterial equivalent of mating, in fact it is simply the transfer of genetic material from a donor cell to a recipient cell. Escherichia coli genes affecting recipient ability in. Replication of a bacterial plasmid and an episome in. We can now summarize the various aspects of the conjugation cycle in e.
Structure and function of the f factor and mechanism of. You have performed the following mating experiment using hfr and f strains of escherichia coli. The f factor is not the only plasmid that can mediated conjugation but it is generally. Since then, f and related f like plasmids have served as role models for bacterial conjugation. Role of dna transcription in the initiation of escherichia coli sex factor f dna replication. Dna transfer by bacterial conjugation springerlink. It is about 30 pm long which is about 140 of the length of the bacterial e. Uses of transposable elements and maps of known insertions.
They are sometimes called sex pili, in analogy to sexual reproduction, because they allow for the exchange of genes via the formation of mating pairs. Bacterial sex, or conjugation, is a central mechanism underlying the proliferation of antibiotic resistance. F factor conjugation is a true type iv secretion system. It became apparent that an hfr strain results from the integration of the f factor.
The f factor is carried on the f episome, the first episome to be discovered. Coli 1 has vancomycin resistance on the chromosome and a plasmid with the f factor as well as streptomycin and ampicillin resistance. The conjugation system of f, the fertility factor of. Structure and function of the factor and mechanism of conjugation. However, the site of sex factor integration was found to. It is a bacterial dna sequence that allows a bacterium to produce a sex pilus necessary for conjugation. The f factor replicates as one strand is transferred. It may become infected with an extrachromosomal genetic element a plasmid called the f factor which mediates certain events such as the synthesis of a pilus the f or sex pilus, and the rapid infection of all susceptible bacteria with this f factor.
The integrated f factor occasionally leaves the chromosome of an hfr cell. The f factor is itself the genetic element which is passed from donor to recipient cells during conjugation. Classic examples of plasmidborne genes are those provid ing bacterial resistance to toxic. Bacterial genetics biology encyclopedia cells, body. Structural hierarchy and complexity of rna illustrated by the gtpase center rna from escherichia coli. Use of the technology led to our initial understanding of the circular bacterial chromosome carrying escherichia coli s array of genes and of the recombination process whereby these genes could be. These f factors are approximately 105 basepairs in size. Recall that most hfrs arise via homologous recombination between is sequences is2, is3, and tn that are present on both.
The f plasmid or f factor is a large, 100kbp, circular conjugative plasmid of escherichia coli and was originally described as a vector for horizontal gene transfer and gene recombination in the late 1940s. Escherichia coli genes affecting recipient ability in plasmid conjugation. One way of introducing a heritable change into a bacterial genome is bacterial conjugation, in which an f plasmid is transferred to an f. Remember, in bacterial conjugation, f plasmids are generally transferred, not the entire bacterial genome. Presence of f factor in conjugation of bacteria genetics. For example, in a h igh f requency recombinant hfr e. Dna processing reactions in bacterial conjugation erich lanka and brian m. However, it is not sexual reproduction, since no exchange of gamete occurs, and indeed no generation of a new organism. Conditions and mutations affecting the maintenance and replication of plasmid dna in escherichia coli 15. Coli strain carrying plasmid 1 is mixed with an f e. Bacterial conjugation is also known as a type iv secretion system. Bacterial plasmids originating in a wide range of genera are being studied from a variety of perspectives in hundreds of laboratories around the globe. Bacterial sex, now termed conjugation, is widely recognized as a predominant mechanism underlying the rapid and widespread transmission of antibiotic resistance genes and the evolution of untreatable superbugs 2.
Study 35 exam 4 bacterial genetics flashcards from jordan w. Bacterial conjugation an introduction to genetic analysis ncbi. Bacterial conjugation an overview sciencedirect topics. Bacterial transformation is defined as the heritable change in the properties of bacteria caused by the uptake of naked dna. The f factor encodes genes for sexual pili, thin rodlike structures with which fcarrying male or donor bacteria attach to f. Finally, conjugative transposons can be transferred from one bacterium to another. The bacterium without f factor is the recipient or f ve strain or recipient.
Bacterial conjugation is the transfer of genetic material between two bacterial cell via direct celltocell contact. The fertility factor allows genes to be transferred from one bacterium carrying the factor to another bacterium lacking the factor by conjugation. Bacterial conjugation a historical perspective springerlink. Asmscience spread and persistence of virulence and. The origin point of replication in f factor for transfer of dna into the. Explain these results the best explanation is that the integrated f factor of the hfr looped out of the bacterial chromosome abnormally and is now an f. Bacterial conjugation transfer of the f plasmid hd. The phenomenon of conjugation in bacteria provides one of the cornerstones of bacterial genetics. When donor f cells mate with recipient f cells, genomic dna is transferred from donor to recipient. The conjugation system of f, the fertility factor of escherichia coli.
Coll 2 has naladixic acid and tetracycline resistance on the chromosome. Temperaturesensitive conjugation defective f factor inescherichia coli e. In the experiment performed, conjugation was studied in e. A kind of infectious transfer of the f factor seemed to be taking place. Pittard school ofmicrobiology, university ofmelbourne, parkville, victoria, australia received for publication 1 august 1969 amutant strain ofescherichia coli k12which is unable to transfer genetic material at 42 chas been isolated. This takes place through a pilus it is a mechanism of horizontal gene transfer as are transformation and transduction although these two other mechanisms do not involve celltocell contact. Bacterial conjugation modern genetic analysis ncbi bookshelf. Athe colonies may be due to back mutation reversion.
The f factor, which is a small circular molecule of dna plasmid, controls the synthesis of f pili that connect donor and recipient cells during conjugation. Bacterial conjugation, in which dna is transferred from one bacterium to another, was first reported in 1946 and found to be mediated by the f factor 1. The role of is elements in mediating the integration of episomes is well documented in the case of the f factor in e. These elements are well known for carrying special genes that confer important survival properties, frequently neces sary under atypical conditions. Recipient cell conjugative plasmid bacterial genetic bacterial conjugation. By agreement with the publisher, this book is accessible by the search feature, but. By agreement with the publisher, this book is accessible by the search feature. In the 1940s, lederberg and tatum ushered in the era of bacterial genetics with reports of sexual mating orchestrated by the escherichia coli f fertility factor.