Bacterial Gene Transfer

Flashcards covering key vocabulary terms related to bacterial gene transfer, including transformation, conjugation, recombination, transduction, restriction and modification, CRISPR, and mobile genetic elements, based on the provided lecture notes.

Mosaic Nature of Genomes

A characteristic of microbial genomes, revealed by bioinformatic studies, indicating a mix of genomic islands, inversions, deletions, paralogs, and orthologs, resulting from heavy horizontal gene transfer, recombinations, and mutagenic/DNA repair strategies.

Transformation

The process of importing free DNA into bacterial cells, first discovered by Frederick Griffith in 1928, providing the initial clue that gene exchange can occur in microorganisms.

Competent Cells

Bacterial cells that are capable of natural transformation, meaning they can take up free DNA from their environment.

Artificial Transformation

A method of inducing competence in cells that are not naturally competent, often involving perturbing the cell membrane by chemical (e.g., CaCl2) or electrical (electroporation) methods.

Transformasome Complex

A protein complex used by Gram-positive bacteria to transform DNA.

Conjugation

The transfer of DNA from one bacterium to another following cell-to-cell contact, often initiated by a specialized pilus from the donor cell.

Pilus

A special appendage protruding from the donor cell that typically initiates conjugation by making contact with a recipient cell.

Transferable Plasmids

Special plasmids containing genes needed for pilus formation and DNA export, which are required for conjugation.

Fertility Factor (F factor)

A well-studied example of a transferable plasmid in Escherichia coli, containing two replication origins (oriV and oriT) and genes for conjugation.

F+ Cell

A donor bacterial cell that possesses the fertility factor (F factor) plasmid, capable of initiating conjugation.

F- Cell

A recipient bacterial cell that lacks the fertility factor (F factor) plasmid.

Hfr (High-Frequency Recombination) Strain

A bacterial cell where the F-factor plasmid has integrated into the chromosome, making it capable of transferring chromosome parts into a recipient cell during conjugation.

Recombination

The process by which two different DNA molecules in a cell combine, occurring via generalized or site-specific mechanisms.

Generalized Recombination

A type of recombination that requires a considerable stretch of homologous DNA sequences between the two recombining molecules.

Site-Specific Recombination

A type of recombination that requires very little sequence homology between DNA molecules, but needs a short sequence recognized by a dedicated recombination enzyme.

RecA

A central protein in generalized recombination (also called synaptase) that scans DNA for homology, aligns homologous regions, and forms a triplex DNA molecule.

Cointegrate Molecule

A molecule produced by a crossover between donor and target DNA molecules during site-specific recombination.

Agrobacterium tumefaciens

A bacterium known for transferring genes across biological domains (to plants) by causing crown gall disease, utilizing a tumor-inducing plasmid (Ti).

Tumor-Inducing Plasmid (Ti)

A plasmid found in Agrobacterium tumefaciens that can be transferred via conjugation into plant cells, causing crown gall disease.

Transduction

A process in which bacteriophages accidentally carry host DNA from one bacterial cell to another as an offshoot of their life cycle.

Generalized Transduction

A type of transduction that can transfer any gene from a donor bacterial cell to a recipient cell.

Specialized Transduction

A type of transduction that can transfer only a few closely linked genes between bacterial cells.

Restriction and Modification System

A bacterial protection system involving enzymatic cleavage (restriction) of alien DNA by restriction endonucleases and protective methylation (modification) of host DNA.

Restriction Endonucleases

Enzymes that cleave alien DNA as part of the restriction and modification system; Type II generally recognizes palindromic DNA sequences and cleaves at those sites.

CRISPR

Clustered regularly interspaced short palindromic repeats; a microbial immune mechanism that targets DNA matching noncoding RNAs for degradation, working similarly to RNA interference.

CRISPR Cassette

Consists of repeats and spacers that do not encode proteins, located near CRISPR-associated gene families that do encode proteins, functioning in spacer acquisition, crRNA processing, and effector stages.

Mobile Genetic Elements

DNA sequences that can move from one DNA molecule to another, existing in virtually all life-forms and able to move within and between chromosomes.

Transposable Elements

Specific mobile genetic elements that move from one DNA molecule to another.

Insertion Sequence (IS)

Simple transposable elements containing only a transposase gene, flanked by short inverted repeat sequences that serve as targets for the transposase enzyme.

Transposase Gene

A gene encoded within an insertion sequence (IS) element that catalyzes the movement of the transposable element.

Replicative Transposition

One of two mechanisms by which IS elements transfer, where a copy of the transposable element is made and inserted into a new location while the original remains.

Nonreplicative Transposition

One of two mechanisms by which IS elements transfer, where the transposable element excises itself from one location and inserts into a new one without replication.

Transposons

Complex transposable elements that carry additional genes, such as drug resistance genes, beyond those required for transposition (e.g., composite, complex, or conjugative transposons).