Micro 3

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Characteristics of bacterial DNA

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is not membrane bound. Transcription and translation ca be coupled in bacteria

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Advantages of bacteria for understanding genetics

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acteria are haploid
 Short generation times
 Asexual reproduction
 Colony growth on agar plates
 Colony purifications
 Easy to store bacterial stocks  Many types of genetic exchange

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Wild type

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parent bacterial strain OR the functional form of a gene

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Phenotype:

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observable properties of organism

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Genotype:

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actual sequence of DNA

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Allele:

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Allele:

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Base mutations and its detection

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Mutations like missense mutations are difficult or impossible to see in plating

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Base substitution characteristics

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May or may not change AA, introduce STOP

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Frame shift characteristics

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Change ORF, often truncates protein

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Prototroph

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an organism with a wild-type complement of genes enabling it to grow with a simple requirement of nutrients

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Auxotroph:

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a mutant unable to synthesize a small molecule - requires supplements for growth on simple lab media (ex. Met auxotroph)

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Fastidious organisms:

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some bacteria have complicated growth requirements and can be difficult to grow in cultur

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Can bacteria have more than one plasmid?

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yes

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What are some characteristics of plasmids

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Extrachromosomal
1.5-600Kb
Autonomously replicate
Dependent on host replication mechanism

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Plasmid dna material can be

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circular or linear

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Plasmids replication mechanism

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Plasmid maintain by partitioning mechanisms ( they replicatein each daughter cell) they can also integrate into the bacterial genome. Some plasmid confer metabolic functions, immunity to antibodies,

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Fertility or F plasmids

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contain tra genes, capable of transfer by conjugation

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Resistance (R) plasmids:

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confer resistance to antibiotics or poisons

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Col plasmids

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encode bacteriocins, or compounds that kill other bacteria

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Degradative plasmids:

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confer ability to digest unusual substances, ie: toluene

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Virulence plasmids:

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confer ability to cause disease

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Some plasmid carry two genes controlled by a single transcript. One is an antitoxin and toxin. This is known as addiction systems. How does it work?

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Addiction system as long as it is in good shape both genes synthesized. If plasmid is not replicated along the host, plasmid breaks down, and toxin is released to kill host

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Mobile transposons need a special element knwon as

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Introduction sequences

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IS elements and transposons can insert within

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nactivate coding sequences

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transposition via IS elements is

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tightly regulated and occurs rarely so as not to kill host organism

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IS elements structures

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Flanked by
Insertion repeats. Transposae have sequences preferences to integrate into. Once they plasmid integrates the target sequence is duplicated this allows recognition of transposon

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Simple insertion sequences characteristics

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small (150 to 1,500 bp), code for transposase

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Complex Transposons characteristics

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size up tp 80 kb
code for one or more insertion enzymes (transposase and resolvase)
drug resistance or other selectable genes

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Self-Transmissible Transposons

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share properties of transmissible plasmid recently discovered in Bacteroides transfer of transposon may be induced by exposure to antibiotics

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transposons can generate loss of function gene mutations, which is useful to

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detect genes and make mutations.

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Bacteriophages

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•Viruses that infect bacteria •Essentially nucleic acid wrapped in protein and/or membrane coat •Both lytic and lysogenic lifestyles

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Bacteriphages can have 2 faiths

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Lytic -- the host cell is lysed OR
Lysogenic (Temperate) -- the phage genome is integrated into the host chromosomal DNA
Bacteriophages are host specific

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Alpha phage characteristic

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Linear genome of ~48 kb that circularizes after infection. Two lifestyles - lytic & lysogenic.

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Alpha phage lytic cycle

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-Bacteriophage attaches to cell and locates receptor in cell membrane
-Virus then injects its dna into the host, a bacteria in this case
-Viral capsids are assembled. Viral DNA is then packaged into the viral capsids, followed by the completion of the viral particle
-A viral lysozyme is produced which degrades the bacterial membrane and releases the mature viruses

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Alpha phage lysogenic infection cycle

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The bacteriophage injects its DNA into the cell
-ATT sequence of viral DNA pairs up with the bacterial ATT sequence
-Viral DNA continues to incorporate into the bacterial DNA. The cell with integrated viral DNA is called lysogen. A virus capable of creating a lysogen is called lysogenic virus.
-Cellular chromosome replicates and cell division then occurs.

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Lysogenic virus can be induced by several mechanisms such as

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ultraviolet radiation or other DNA damaging reagents.
-Repressor is destroyed and the virus excised from the chromosome and undergoes the lytic process.
-A viral lyzsosyme is produced which degrades the bacterial membrane and releases the mature viruses

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Examples of lysogenic phages and toxin production

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Cornybacterium diphtheria Diphtheria toxin
Escherichia coli Shiga toxin
Vibrio cholera Cholerae toxin
Clostridium botulinum BoTox

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Escherichia coli mechanism

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when bacteria senses antibody (Quinolone) is around, it expresses Shia toxins and delivers xprotein into host cell leading to death of
Host cell.

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How can bacteriophage be used to selectively kill pathogenic bacteria?

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Pages kill dividing an no dividing cells. They can be really specific to the pathogen. Phage can also treat multiresistant drug bacteria

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examples of phage therapy

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BioTector - animal feed for control of
Salmonella in poultry
EcoShield - targets E. coli O157:H7 in food & food processing facilities
Biocontrol (clinical trials) - to reduce Pseudomonas ear and lung infections

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Pro's of phage therapy

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Can target antibiotic resistant bacteria Can selectively kill pathogen vs flora Can reduce biofilms on catheters

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Cons of phage therapy

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Difficult to treat deep tissue infections
Antibodies against phage may reduce effectiveness