Bacterial Genetics

Front 1

lysogenic conversion:

Back 1

acquisition of prophage confers new phenotypic property upon host cell

Front 2

conjugative plasmid

Back 2

encodes conjugal transfer system; large single copy/chromosome

Front 3

transposable genetic elements = transposons (Tn):

Back 3

pecific DNA sequences containing one or more antibiotic resistance genes - can repeatedly insert at many different sites w/in chromosomal genome or plasmid (transposition)
-insertion elements (Is): DNA elements not carrying antibiotic resistance genes
-transposase; inverted repeats; direct repeats
-give genetic flexibility

Front 4

Genetic transformation

Back 4

-recipient cell takes up naked DNA released by donor cell
-natural transformation occurs in number of bacterial pathogens, including Strep, Haemophilus, Neisseria --> highly efficient process in contrast to artificially induced transformation
-single strand of DNA (usually derived upon lysis of homologous donor cell) enters recipient cell and is integrated into homologous region of recipient DNA, replacing recipient allele
-efficiency depends on properties of transforming DNA and physiological state of recipient cell
-low molec weight dsDNA is most active
-ssDNA has little or no transforming ability
-number of transformants obtained dependent on concentration of transforming DNA
-for successful transformation, recipient cell must be at certain physiological state = competence to bind DNA --> occurs late in log phase of growth; corresponds w/ production of proteins (competence factor) that act by binding or trapping transformed DNA at specific sites on cell surface
-after binding of DNA to cell surface, endonuclease (in cell memb) degrades one strand and 'propels' that other strand into the cell

-ssDNA then pairs w/ homologous region of recipient chrom and integrates

Front 5

Transduction

Back 5

bacteriophage mediates gene transfer from donor cell to recipient cell - common among members of gram eg Enterobacteriaceae, gram pos Staph aureus and C. diphtheriae (spread diphteria toxin gene between strains)
Generalized Transduction: random fragments of donor bacterial chrom can be transferred to recipient
-bacteriophage infects host bacterium --> initiates lytic cycle --> bacterial chrom broken down into many fragments, picked up and packed into new phage particles --> phage particles released, infect other cell --> new host acquires genes transduced from previous bacteria
Specialized Transduction: specific chrom DNA segments are transferred from donor to recipient
-requires viral integration and involves transduction of specific chrom genes adjacent to viral itnegration site
-phage DNA aways inserts into host chrom in particular site --> when phage DNA replicates it takes bacterial genes from either side of site and packs them w/ own DNA into new phages
-only genes adjacent to insert site, not genes from other parts of host chrom, are transduced

Front 6

Conjugation

Back 6

genetic exchange mediated by plasmids
-requires cell-cell contact to accomplish process
-conjugative plasmids carry genes encoding sex pilus--> required for DNA transfer between donor and recipient cells
-conjugative plasmids in donor (male) encode sex pilus (F pilus) --> forms bridge w/ recipient (female) --> allows conjugative plasmids and sometimes pts of chrom DNA to transfer genes from donor to recipient cells w/o exposure to extracellular environment (F DNA - begins at oriT) --> after transfer, both cells have copy of F factor

-F factor - sex factor
-R factor - Resistance factor

Front 7

integrons

Back 7

= recombination hot spots for site specific recombination events between largely nonhomologous sequences of DNA; genetic element that possess a attI site - where gene casssettes can be integrated by site specific recombination; and which encodes enzyme integrase that mediates site specific recombination
-many integrons also accommodate gene for sulfonamide resistance (sul) at one end
-gene cassettes: norm contain only one gene and short sequence - 59 base element - that functions as specific recombination site - lack promoters, expressed from specific promoter on integraon beside attI
-integrons incorporated into replicons: transposons and plasmids

Front 8

Pathogenicity Islands: Pais

Back 8

- specific regions of chromosomal DNA; represents large fragments of DNA that include number of virulence genes --> result from chrom integration of mobile genetic elements
-single bacterial cell can carry more than one pathogenicity island
-genes encoding type III secretion systems of gram neg bacteria often located on pathogenicity islands

Characteristics of Pais:
-carriage of virulence genes
-presence in path strains and absence in less pathogenic strains of one species or related species
-different GC content compared to DNA of host
-occupation of large chrom regions (>30kb)
-represent compact, discrete genetic units, often flanked by direct repeats
-associated w/ tRNA genes and/or insertion sequence (IS) elements at boundaries
-presence of (often cryptic) mobility genes (IS elements, integrases, transposases, origins of plasmid replication)
-instability

Front 9

Gram Pos Bacteria

Back 9

can't wash out stain --> purple
-thick cell wall, lots peptidoglycan
-high osmolality
-require very thick/rigid cells walls

Front 10

Gram Neg Bacteria

Back 10

wash out violet --> pink from safran
-very thin peptidoglycan layer
-LPS/outer membrane - has POREs
-more complex