Microbial Genetics: Focus On Bacterial Recombination

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GENETICS. What are Genes?

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-Genetics studies genes!
-Genes are units of information made of DNA; they carry information about particular traits. They are also the basis of heredity; they are copies and passed on to future generations.
-Genetic processes are fundamentally similar in all organisms, from bacteria to people.

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DNA Structure

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-DNA is a polymer of nucleotides, which come in four varieties; A,G, C, T.
-In nature, DNA is found as a double-helix, in which two anti-parallel strands are joined by hydrogen bonds between the bases (A-T and G-C combinations)

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THE CENTRAL DOGMA OF MOLECULAR BIOLOGY

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-Information flows from DNA to RnA to Proteins
-DNA copies itself before cell division in a process called replication
-DNA makes RNA copy (mRNA) of itself during the process of transcription
-Messenger RNA directs the synthesis of a protein during translation.
-A gene holds the information necessary to build a particular protein.

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-Do bacteria have sexual lifes cycles? What classifies a sexual life cycle?

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-Bacteria NEVER, EVER have sexual relations or sexual life cycles!

-Recombination is usually caused by sexual processes. -->increases variation.

-Bacteria have a short generation time, which increases mutations, thus causing mutations and increases variation.

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Transformation

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-Discovered by Griffith in an experiment that eventually led to the idea that DNA is the genetic material.
-His experiment involved Streptococcus pneumoniae bacteria and mice.
-Smooth strains of S. pneumoniae produces illness in mice; rough strains did not (we now know this was because of the capsule)

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Gram Postivie Bacteria

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-Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain (safranin or fuchsin) and appearing red or pink. Gram-positive organisms are able to retain the crystal violet stain because of the high amount of peptidoglycan in the cell wall. Gram-positive cell walls typically lack the outer membrane found in Gram-negative bacteria.

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Gram Negative Bacteria

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Gram-negative bacteria are those bacteria that do not retain crystal violet dye in the Gram staining protocol.[1] In a Gram stain test, a counterstain (commonly safranin) is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color. The test itself is useful in classifying two distinct types of bacteria based on the structural differences of their cell walls.On the other hand, Gram-positive bacteria will retain the crystal violet dye when washed in a decolorizing solution.

Many species of Gram-negative bacteria are pathogenic, meaning that they can cause disease in a host organism. This pathogenic capability is usually associated with certain components of Gram-negative cell walls, in particular the lipopolysaccharide (also known as LPS or endotoxin) layer.[1] In humans, LPS triggers an innate immune response characterized by cytokine production and immune system activation. Inflammation is a common result of cytokine (from the greek cyto=cell, kinesis=movement) production, which can also produce host toxicity.

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Griffith's Experiment (the 4 scenarios)

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1) - Inject live smooth strain bacteria into mouse = DEATH

2) - Inject live rough strain bacteria into mouse = NO PROBLEM

3) - Inject dead smooth strain bacteria into mouse = NO PROBLEM

4) - Mix living rough strain bacteria with dead smooth strain bacteria, inject into mouse = DEATH!

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In Griffith's Experiment, why does DEATH result when you mix living rough strain bacteria with dead smooth strain bacteria?

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-Something from the smooth cells was able to TRANSFORM the rough cells into smooth cells. -> DNA

-Transformation is defined as the uptake of naked DNA by a cell.

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CONJUGATION:
definition, how it was discovered.

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-Conjugation is defined as the transfer of genetic material from one bacterial cell (the donor) to another (the recipient) by direct contact.
-Conjugation was initially discovered while studying a plasmid called the F factor. (fertility factor)
-During conjugation, the plasmid copies itself, and directs the formation of a pilus, through which the copy (or a part of it) moves to a recipient cell.
-Cells containing the F factor are referred to as F+ and can change cells without it (F-) to F+.
-If the F factor becomes integrated into the bacterial chromosome, we call that an Hfr (high frequency) strain because when it conjugates it causes a high frequency of recombination of bacterial genes.

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Transduction

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-Transfer of bacterial genes from one cell to another mediated by a bacteriophage (a virus that infects bacteria)
-When the virus infects a bacterial cell, it replicates its own DNA and degrades the bacterial DNA.
-Sometimes, by mistake, bacterial genes become incorporated into the new infective phage particles.
-If this phage now infects another bacterium, these new genes can be tranferred to the new cell, often allowing it to express a new trait. -->increases variation.

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2 types of Transduction?

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-Generalized - any bacteriophage may be involved and any genes may be transferred.

-Specialized - only temperate phages may be involved (phages which integrate into the bacterial chromosome), and only the genes adjacent to their integration sites may be transferred.

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Bacteriophage

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Virus that infects a bacteria

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Temperate Phage

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Bacteriophages that display the lysogenic lifecycle.