Ch. 13 Key Terms

Front 1

prokaryote

Back 1

single-celled organism whose genome is not enclosed in a nucleus

Front 2

pathogen

Back 2

a microorganism that causes disease in its host

Front 3

core genome and pangenome

Back 3

Genes shared by all strains of a given bacterial species are the core genome of that species; the core genome plus all the genes found in some strains and not others of the species constitutes the pangenome of that species.

Front 4

IS elements and Tn elements

Back 4

Small bacterial transposons that include genes needed for their own transposition but do not carry any genes for other functions in the host cell are called insertion sequences, or IS elements; larger bacterial transposons carrying transposase and drug resistance genes and flanked by IS elements are called Tn elements.

Front 5

plasmids and episomes

Back 5

Small circles of double-stranded DNA that can replicate in bacteria independently of the bacterial chromosome are plasmids; plasmids that can integrate into the bacterial chromosome (e.g. the F factor) are episomes.

Front 6

bacteriophages (or phages)

Back 6

viruses that infect and propagate in bacteria. Some phages can insert into the bacterial chromosome; the integrated phage genome is called a prophage, and the bacterium housing the prophage is called a lysogen.

Front 7

lysis

Back 7

the process during phage propagation in a host bacterium where the bacterial cell breaks open, releasing progeny phage. Fluid containing lysed bacterial cells and thus progeny phage are called lysates.

Front 8

minimal medium

Back 8

an aqueous solution containing a sugar and inorganic salts that can support growth of prototrophic (wild-type) bacteria

Front 9

Metagenomics

Back 9

collective analysis of genomic DNA from natural communities of microorganisms

Front 10

prototrophs and auxotrophs

Back 10

Wild-type bacteria that can grow on minimal medium because all of their biosynthetic pathway genes are functional are prototrophs; bacteria that require a supplement to minimal medium because they have a mutation in a biosynthetic pathway gene are auxotrophs.

Front 11

screens and selections

Back 11

In genetic screens, individual organisms (or clones) are tested for the phenotype in question; in genetic selections, conditions are devised so that only those organisms with the phenotype in question can survive.

Front 12

horizontal gene transfer

Back 12

the introduction and incorporation of DNA into a recipient from a different individual or from a different species

Front 13

transformation

Back 13

one of ways in which bacteria share genes; occurs when DNA, either linear DNA fragments or circular plasmids from the donor is taken up by the recipient; recipient is called a transformant. Spontaneous transformation is called natural transformation. To increase transformation efficiency and to make it happen in bacterial species that do not undergo natural transformation, researchers can use various techniques to make bacterial cell walls and membranes permeable to DNA: process called artificial transformation.

Front 14

conjugation

Back 14

another way in which bacteria share genes. In conjugation, the temporary connection of two bacterial cytoplasms allows DNA transfer, through replication, from the donor to the recipient. After conjugation, the recipient is called the exconjugant.

Front 15

transduction

Back 15

yet another way in which bacteria share genes. Transduction is a mechanism of horizontal gene transfer where bacterial donor DNA is packaged in phage during lysis, and this DNA is then transferred to a recipient bacterium upon subsequent infection; recipients are known as transductants. In generalized transduction, any portion of a bacterial genome can be transferred; in specialized transduction, only bacterial genes located next to insertion sites of prophages are transferred.

Front 16

F factor (F plasmid, F episome)

Back 16

a large plasmid that carries genes required for conjugation and gene transfer. Bacteria that have an F factor are called F+ bacteria and serve as the donors during conjugation; the F- recipients lack an F factor. Strains in which the F factor has integrated into the bacterial chromosome are known as Hfr bacteria because they transfer genes from the donor bacterial chromosome at high frequency.

Front 17

Merodiploid

Back 17

bacteria that are partially diploid because they house an extra copy of some bacterial genes on a plasmid such as the F factor

Front 18

gene targeting

Back 18

using cloned, genetically engineered DNA to alter the base pair sequence of a genome in a particular manner at a specific location through homologous recombination