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  • Why does a bacterial cell make environmental DNA brought into the cell into a single-stranded form?

Transduction

Viruses that infect bacteria ( bacteriophages ) may also move short pieces of chromosomal DNA from one bacterium to another in a process called transduction (see [link] ). Recall that in generalized transduction , any piece of chromosomal DNA may be transferred to a new host cell by accidental packaging of chromosomal DNA into a phage head during phage assembly. By contrast, specialized transduction results from the imprecise excision of a lysogenic prophage from the bacterial chromosome such that it carries with it a piece of the bacterial chromosome from either side of the phage’s integration site to a new host cell. As a result, the host may acquire new properties. This process is called lysogenic conversion. Of medical significance, a lysogenic phage may carry with it a virulence gene to its new host. Once inserted into the new host’s chromosome, the new host may gain pathogenicity. Several pathogenic bacteria, including Corynebacterium diphtheriae (the causative agent of diphtheria) and Clostridium botulinum (the causative agent of botulism), are virulent because of the introduction of toxin-encoding genes by lysogenic bacteriophages, affirming the clinical relevance of transduction in the exchange of genes involved in infectious disease. Archaea have their own viruses that translocate genetic material from one individual to another.

  • What is the agent of transduction of prokaryotic cells?
  • In specialized transduction, where does the transducing piece of DNA come from?

The clinical consequences of transduction

Paul, a 23-year-old relief worker from Atlanta, traveled to Haiti in 2011 to provide aid following the 2010 earthquake. After working there for several weeks, he suddenly began experiencing abdominal distress, including severe cramping, nausea, vomiting, and watery diarrhea. He also began to experience intense muscle cramping. At a local clinic, the physician suspected that Paul’s symptoms were caused by cholera because there had been a cholera outbreak after the earthquake. Because cholera is transmitted by the fecal-oral route, breaches in sanitation infrastructure, such as often occur following natural disasters, may precipitate outbreaks. The physician confirmed the presumptive diagnosis using a cholera dipstick test. He then prescribed Paul a single dose of doxycycline, as well as oral rehydration salts, instructing him to drink significant amounts of clean water.

Cholera is caused by the gram-negative curved rod Vibrio cholerae ( [link] ). Its symptoms largely result from the production of the cholera toxin (CT), which ultimately activates a chloride transporter to pump chloride ions out of the epithelial cells into the gut lumen. Water then follows the chloride ions, causing the prolific watery diarrhea characteristic of cholera. The gene encoding the cholera toxin is incorporated into the bacterial chromosome of V . cholerae through infection of the bacterium with the lysogenic filamentous CTX phage, which carries the CT gene and introduces it into the chromosome on integration of the prophage. Thus, pathogenic strains of V. cholerae result from horizontal gene transfer by specialized transduction.

  • Why are outbreaks of cholera more common as a result of a natural disaster?
  • Why is muscle cramping a common symptom of cholera? Why is treatment with oral rehydration salts so important for the treatment of cholera?
  • In areas stricken by cholera, what are some strategies that people could use to prevent disease transmission?
Micrograph of curved rods.
A scanning electron micrograph of Vibrio cholerae shows its characteristic curved rod shape.

Questions & Answers

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removal of nucleotide bases from DNA is damage n addition or insertion of bases in DNA is repair.
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replication is a term related to generation of new DNA from a parental DNA.
Rashmi
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toxins released inside the cell or a body is endotoxin n toxins released outside the cell or a body is exotoxin.
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the study of viruses
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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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