Lesson 7: Genetic Analysis and Mapping in Bacteria and Phage Terms

binary fission

process in which the bacterial chromosome replicates and a copy is distributed to each of the progeny cells

colony

a cluster of millions of bacterial cells all derived from a single cell

minimal medium

one medium containing glucose as the sugar source along w/ a nitrogen source, some inorganic material, and water

phototrophs/phototrophic strains

wild-type cells of many bacterial species that are able to grow in minimal medium and produce all of the compounds required using energy from glycolysis

auxotrophs/auxotrophic strains

strains that lack some of the genes required to grow on minimal medium and instead obtain essential nutrients from their hosts

complete medium

medium containing glucose and a nitrogen source along w/ all components requiredsu

supplemented minimal medium

minimal medium to which has been added the specific compound the auxotrophic strain is unable to make on its own

replica plating

a process of transferring some cells from each of the bacteria on an original growth plate to one more other growth plates

plasmids

small double-stranded circular DNA containing non-essential genes that are used infrequently or under special occasions

F (fertility) plasmid

contains genes that promote its own transfer from a donor bacterium to a recipient

R (resistance) plasmid

carries antibiotic resistance genes that can be transferred from donors to recipients

donor

bacterium that donates replicated DNA

recipient

bacterium that requires replicated DNA

conjugation

transfer of replicated DNA from a donor bacterium to recipient through temporary contact, creating a bridge between the cells and initiating DNA transfer across the bridge

transfromation

uptake of DNA derived from a donor cell from the growth medium of the recipient

transduction

transfer of DNA by way of a bacteriophage

conjugation pilus

hollow tube that physically connects donor and recipient

F+ cells

donors and in possession of the F factor

F- cells

recipients and not in possession of the F factor

exporter structure

formed from coupling and exporter proteins that form the bridge through which a single strand of F factor DNA will pass through

relaxosome

protein complex responsible for cutting one strand of F factor DNA

exconjugant cells

recipient cell that has had its genetic content modified by receiving DNA from a donor cell

insertion sequence (IS) elements

DNA sequences that when shared by an F plasmid and a bacterial chromosome are locations for recombination between the two

origin of transfer (oriT)

site within the F factor sequence where transfer to the recipient cell is initiated

T (transfer) strand

DNA strand of T-DNA cleaved to initiate the transfer of plasmic DNA during rolling circle replication

rolling circle replication

unidirectional mode of DNA replication used to replicate plasmid molecules in which the replicating molecule appears to reel off its nontemplate DNA strand, using the other as a template for replication

high-frequency recombination (Hfr)

donor strains that transfer donor bacterial genes to recipient bacteria at a very high rateHfr

Hfr chromosome

chromosome that has the F factor from Hfr strains integrated into its own chromosome

selective growth medium

medium containing compounds that permit any exconjugants w/ specific genotypes to grow and that also prevent the growth of donor/recipient cells

interrupted mating

cessation of conjugation caused by breakage of conjugation pilus, takes place during naturally occurring conjugation

time-of-entry mapping

testing gene transfer at time intervals to map the order of donor genes and determine the distances between the genes

F’ (F prime)

contains a fractional but altered F factor derived from imperfect excision of the F factor out of the Hfr chromosome

F’ factor

extrachromosomal fertility plasmid into which a portion of the donor bacterial chromosome has been incorporated

F’ cells

donor cells carrying an F’ factor

partial diploids

exconjugants that one diploid for genes transferred to it on the F’ plasmid

lysis

breakage of a donor cell and the release of fragmented DNA from the donor chromosome

cotransformation

simultaneous transformation of two or more genes

transductant

formed when the donated DNA is integrated into the recipient’s chromosome by homologous chromosomes

lytic cycle

when infection by a bacteriophage leads to the lysis of the host cell

temperate phages

bacteriophages that are capable of a temporary alternate life cycle that leads to the temporary integration of the phage chromosome into the bacterial host chromosome

lysogeny

temporary alternative life cycle that leads to temporary integration of the phage chromosome into the bacterial host chromosome

lysogenic cycle

cycle where lysogeny can persist for many bacterial replication/division cycles but eventually comes to an end and lytic cycle resumes

generalized transduction

transduction of a random segment of a donor chromosome into a recipient cell by a transducing phage

generalized transduction phages

formed when a random piece of donor bacterial phage DNA of the appropriate length is mistakenly packed into the phage head

cotransduction

simultaneous transduction of two or more genes contained on a donor DNA fragment into a recipient cell, where it undergoes homologous recombination to be spliced into the transductant chromosome

cotransduction frequency

frequency of cotransduction depends on how close the two genes are to one another on the donor chromosome

selected marker screen

an experimental method used to detect microorganisms w/ a specific genotype and can identify one of the donor alleles of interest

unselected marker screen

experimental technique used to screen minimal genotypes

cotransduction mapping

method of mapping donor bacterial genes based on frequency of contransduction

att site

site of integration in a DNA sequence that is identical in the bacterial/phage chromosome

specialized transducing phage

transduction from a donor cell to a recipient cell of a few select genes located near the site of bacteriophage integration

genetic fine structure

composition of genes at the level of their molecular building blocks

reversible mutants

can undergo spontaneous revision back to wild-type

nonreversible mutants

never reverted

reversions

revertible mutations that are caused by DNA base sequence substitutions which can be changed back to wild-type sequence

deletion mapping

method for mapping genes utilizing partial chromosome deletions w/ known locations to expose recessive mutants

lateral gene transfer (LGT)

transfer of genetic material between individual bacteria/archaea and other organisms

genomic islands

genome segments that differ in sequence makeup from the surrounding genome sequence

pathogenicity islands

subtype of genomic islands that contain multiple genes for proteins that promote the ability of bacteria to invade the body of a host