Bacterial Gene Transfer and Phage Mechanisms CHAP6

Vocabulary flashcards covering key terms and definitions from bacterial gene transfer, transformation, transduction, and related genetics concepts from the notes.

Conjugation

One-way transfer of genetic material from a donor to a recipient in bacteria, typically via a conjugation pilus; can involve the F factor or chromosomal genes (as in Hfr transfer).

Conjugation pilus

A hollow tube formed by a donor cell that enables DNA transfer to a recipient during conjugation.

F factor (F plasmid)

Fertility plasmid that carries genes necessary for conjugation; about 100 kb and ~40 genes; converts donors to F+.

F+ cell

Donor cell that contains the F factor.

F- cell

Recipient cell that lacks the F factor.

Exconjugant

Recipient cell that has acquired donor DNA during conjugation.

Hfr (high-frequency recombination) strain

An F+ cell with the F factor integrated into the chromosome, enabling high-frequency transfer of chromosomal genes (not the whole chromosome).

F factor integration

Insertion of the F factor into the bacterial chromosome at IS elements, creating an Hfr chromosome (episomal when integrated).

Episome

DNA element that can replicate independently or integrate into the chromosome (F factor behaving as an episome when integrated).

IS elements

Insertion sequences that facilitate integration of the F factor into the chromosome and mediate recombination.

oriT

Origin of transfer on the F plasmid where DNA transfer begins during conjugation.

Relaxosome

Protein complex that binds and cleaves the T strand at oriT to initiate transfer in conjugation.

Rolling circle replication

Replication mechanism during conjugation where the T strand is transferred while replication occurs to restore donor DNA.

F factor excision (precise vs aberrant)

Precise excision restores the F factor as an extrachromosomal element; aberrant excision yields an F′ factor that carries adjacent bacterial DNA.

F′ (F-prime) factor

An F factor that carries a piece of bacterial DNA due to aberrant excision; can act as a donor in F′-F mating to form partial diploids.

F- × F′ mating

Transfer of the F′ factor from an F′ donor to an F− recipient, producing a partial diploid (merozygote).

Exconjugant chromosome

Chromosome of an exconjugant that includes donor DNA integrated by recombination during conjugation.

oriT (Origin of transfer)

Site on the F plasmid where transfer of DNA begins during conjugation.

Interruption of mating

Stopping conjugation at intervals to map gene transfer (time-of-entry mapping) in Hfr strains.

Time-of-entry mapping

Mapping donor genes by recording when they first appear in exconjugants during interrupted mating.

Prototroph

Bacterium that can grow on minimal medium; lacks mutations blocking essential biosynthesis.

Auxotroph

Mutant that cannot synthesize a compound required for growth and needs supplemented media.

Minimal medium

Growth medium containing glucose, a nitrogen source, and inorganic material; supports prototrophs.

Complete medium

Growth medium containing all nutrients required for growth (amino acids, nucleotides, etc.).

Replica plating

Technique to transfer colonies from one plate to another to identify auxotrophs by growth on selective media.

R plasmid

Plasmid carrying antibiotic resistance genes that can be transferred to recipient cells.

Plasmids

Extrachromosomal, usually small, circular double-stranded DNA molecules that carry non-essential genes.

High-copy-number plasmids

Plasmids that replicate to many copies per cell.

Low-copy-number plasmids

Plasmids present in one or two copies per cell and often unable to replicate independently of the chromosome.

Bacteriophage

A virus that infects bacteria; can be lytic or lysogenic and act as vectors for gene transfer.

Lytic cycle

Phage life cycle resulting in host cell lysis and release of progeny phages.

Lysogenic cycle

Phage life cycle where the phage genome integrates as a prophage in the host genome; can later enter the lytic cycle.

Temperate phage

Phage capable of both lytic and lysogenic cycles (e.g., λ phage).

Prophage

Integrated phage genome within the bacterial chromosome during lysogeny.

Specialized transduction

Transfer of specific bacterial genes adjacent to the prophage due to aberrant excision; often involves attB/attP.

Generalized transduction

Transfer of random donor DNA fragments by a transducing phage; size-limited by phage head capacity (e.g., P1).

Transducing phage

A phage that carries donor bacterial DNA instead of its own phage DNA.

P1 phage

A well-studied phage used for generalized transduction in E. coli; about 100 kb genome.

AttB / AttP

Sites for lambda phage integration; attB in the bacterial chromosome and attP in the phage genome.

Prophage excision

Removal of the prophage from the host chromosome; can be precise or aberrant, sometimes carrying host DNA.

Cotransduction

Transfer of two or more genes together during transduction due to close proximity on donor chromosome.

Yanofsky cotransduction mapping

Mapping strategy using cotransduction frequencies (e.g., trp operon order: trpE-trpC-trpB-trpA).

Auxotrophy mapping by selection/replica plating

Identifying gene functions by selecting for growth requirements on minimal vs complete media.