Micro E2 NS - Microbiology Exam 2 Spring 2006 Bacterial DNA...

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Microbiology Exam 2 Nicole M. Schmidt Spring 2006 Palmer College 1 Bacterial DNA Pieces DNA pieces which exist separately from the chromosome transfer to other bacterial cells may result in new strains or strains with new traits 2 Types: 1. Plasmids 2. Transposons 1. Plasmid double-stranded DNA molecule with far fewer base pairs than the chromosome forms a loop (except linear plasmid of Borrelia spp.) replicates (referred to as replicon) – even when bacteria is not replicating episomes – plasmids which can integrate into host chromosome Information carried includes genes for: - antibiotic resistance - bacteriocin production = proteins made by bacteria which inhibit closely related species - various types of toxins - ability to metabolize a particular substrate F Plasmid transferred during conjugation DNA which enables bacteria to - make an F-pilus - send a copy or strand of the plasmid DNA across the F-pilus to another bacterial cell RTF Plasmid = resistance transfer factor encodes: - the F plasmid information - DNA (many genes) that enable bacterium to become resistant to various, many antibiotics 2. Transposons pieces of DNA that can travel from: - one place on a chromosome to another place on the chromosome or - to a plasmid and back to the chromosome (act like plasmids, episomes) Consequences of transposon movement: - inactivation of a gene - acquisition of antibiotic resistance information - acquisition of virulence factors - expression of virulence factors - spontaneous mutation (appears as such) - formation of plasmids with multiple genes such as RTF Transfer of DNA results in recombinant cells one-way transfer, from donor cell to recipient cell (not an “exchange”) 3 natural mechanisms: 1. Transformation 2. Conjugation 3. Transduction 1. Transformation naked DNA is picked up from the environment (where dead cells had released it)—live cells incorporate it into their DNA competent cells – only ones that are able to take up naked DNA Griffith 1928 - proved that capsules on Streptococcus pneumoniae bestowed virulence - revealed the ability of cells to pick up naked DNA - in his experiment a piece of DNA from a dead virulent cell was picked up by a non-virulent cell that was then incorporated and used to produce a capsule—proved that DNA is the stuff of inheritance
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Microbiology Exam 2 Nicole M. Schmidt Spring 2006 Palmer College 2 other competent species (Gram + and -): - Haemophilus influenzae - Streptococcus pneumoniae - Bacillus spp. - Neisseria spp. 2. Conjugation F+ cell – “donor” cell which has an F plasmid (loop of DNA, see above definition) F- cell – cell without an F plasmid; recipient cell sequence of events: 1. F+ cell makes an F pilus, connects it to F- cell 2. F plasmid sends single strand of F plasmid DNA into F- cell 3. each cell then synthesizes complementary strand of DNA to result in double stranded loops of DNA (F plasmid has replicated) happens very fast, with a large number of bacteria “infected” in a very short time Hfr Cells high frequency recombination cells—produce many new strains
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