Bacteria Genetic Transfer PDF

Bacteria Genetic Transfer Dr Lorina Badger - Emeka COM - KFU  Intended Learning Outcomes 1 Students should be able to: Know what plasmids, bacteriophages, transposons and pathogenicity islands are.  Know the purpose for Quorum sensing Know the role of plasmids, ph...

Bacteria Genetic Transfer Dr Lorina Badger - Emeka COM - KFU  Intended Learning Outcomes 1 Students should be able to: Know what plasmids, bacteriophages, transposons and pathogenicity islands are.  Know the purpose for Quorum sensing Know the role of plasmids, phages and transposons in gene transfer via: - conjugation, - transformation; - transduction  Intended Learning Outcomes 2 Students should be able to know:  Know the role of recombination in bacteria gene transfer.  Introduction Acquiring genes through genetic transfer provides,  new genetic information to microorganisms and this may help them to survive changing environments  Importance of genetic transfer From a clinical perspective, - it aids in the transfer of antibiotic resistance genes from resistant bacterial to sensitive ones. Plasmids and bacteriophages can also give other factors (such as virulence genes e.g. toxins) to bacteria who previously didn’t have them.  The Bacterial gene and Expression Bacteria have only one chromosome They may also contain extra chromosomal genetic elements such as  plasmids and bacteriophages (bacteria viruses) These elements are independent of the bacterial chromosome and  can be transmitted from one cell to another. Plasmids 1 Antibiotic susceptibility and plasmid profile of clinical isolates of Escherichia coli. Badger-Emeka et al., 2018  Plasmids 2 Plasmids are small genetic elements They can replicate independently of the bacterial chromosome.  They can also provide for genetic change. Plasmids carry genetic information,  Plasmids 3 The F plasmid is important for conjugation  R plasmids which carry genes that confer resistance to certain antibiotics They can be transferred by conjugation from one bacteria cell to another Importance? Without resistance genes for a particular antibiotic,  a bacterium is sensitive to that antibiotic Plasmids Cont’d  Bacteriophages 1 Bacteriophages are bacterial viruses. With either a DNA or RNA genome usually protected by a protein shell. They can survive outside of a host cell and be transmitted from one cell to another. Bacteriophages infect bacterial cells. Bacteriophages 2  Bacteria Chromosome The bacteria genome is the total of genes carried by a bacteria both on it’s Chromosomal and extrachromosomal genetic elements  Pathogenicity Islands Genes may also be grouped in islands, such as  the pathogenicity islands, Which share function or to coordinate their control. Pathogenicity islands are found in:  Gram-negative and Gram-positive bacteria.  Pathogenicity Islands 2 The genes for some virulence mechanisms are organized into a pathogenicity island  Quorum Sensing In a process called quorum sensing,  when a sufficient number (quorum) of bacteria are present and producing a specific small molecule,  virulence and other genes are turned on.  Quorum Sensing Examples  E.g., when sufficient numbers of bacteria (a quorum) are present:  Activation of toxin production and more virulent behaviour by Staphylococcus aureus  is accomplished by the increase in a cyclic peptide concentration.  The biofilm production by Pseudomonas spp. Is triggered by:  critical concentration of N-acyl homoserine lactone (AHL) produced.  Transposons Transposons are transferable genetic elements in the genome, They are mobile in nature  They can jump from one position to the other within the genome. There are two types namely:  replicative and non-replicative transposons  Transposons 2 Transposons are pieces of DNA  they can move from: one location on the chromosome to another,  from plasmid to chromosome or vice versa or from one plasmid to another  Genetic transfer The mechanism by which DNA is transferred from one donor to a recipient In bacteria, genetic transfer can occur in three ways: 1. transformation 2. transduction 3. conjugation A recombination event must occur after transfer in order for the change in genome to be heritable.  Microbial genetic transfer between cells 1. Conjugation 2. transformation 3. transduction  Conjugation Conjugation occurs between members of the same species The process involves an exchange of genetic information. It is a one-way transfer of DNA from donor (male) cell to the recipient cell (female). Conjugation: Fig.  Conjugation Cont’d Plasmids may contain genes that allow a bridge (pilus) to form between two bacteria. Bacteria with these plasmids are F+ The plasmid from the F+ (donor) bacterium is replicated and transferred to the F- (recipient) bacterium  Summary Question 1 Which one of the following method of gene transfer involves direct contact between the bacteria?  A) Conjugation.  B) Transduction.  C) Transformation.  Transformation DNA is released at the death or lysing of bacteria, Other bacterial, of the same species, take up these fragments and  incorporate them into their DNA by recombination This method of transfer is the process of transformation. This genetically transformed cell is called a recombinant cell. TRANSFORM ATION 1 TRANSFORM ATION 2  Transduction This is another method for genetic transfer Here, DNA is transferred from one bacterium to another with the use of a bacteriophage (phage) TRANSDUCTI ON cont’d  Genetic recombination This refers to the exchange between two DNA molecules  It results in new combinations of genes on the chromosome The process involves the crossing over of two homologous chromosomes  Recombination can give rise to genetic diversity in a population. High frequency recombinations Genetic mechanisms of evolution of methicillin- and vancomycin-resistant Staphylococcus aureus (MRSA and MVRSA). Vancomycin-resistant Summary  REFERENCES MEDICAL MICROBIOLOGY.  BY  MURRAY ROSENTHAL PFALLER. 7TH ED. Chapter 13, pg. 125 - 127 ALL IMAGES ARE COURTESY OF GOOGLE 8th Edition: Chapter 13; pg. 121 – 123; 129 - 132