Microbiology researchers conduct a series of experiments to determine how pathogenicity is transmitted among different strains of Streptococcus pneumoniae. In the first experiment, they inject nonvirulent strain A into the peritoneal cavity of laboratory mice and observe no ill effects. In the second experiment, researchers subject virulent strain B to a detergent agent that kills and lyses the bacterial cells. They then inject the lysate into the peritoneal cavity of a new group of mice and again observe no ill effects. During a third experiment, they inject live strain A bacteria in combination with the killed strain B lysate, resulting in death of the mice. Which of the following genetic processes most likely accounts for the observed findings of these experiments?

Question

Microbiology researchers conduct a series of experiments to determine how pathogenicity is transmitted among different strains of Streptococcus pneumoniae.  In the first experiment, they inject nonvirulent strain A into the peritoneal cavity of laboratory mice and observe no ill effects.  In the second experiment, researchers subject virulent strain B to a detergent agent that kills and lyses the bacterial cells.  They then inject the lysate into the peritoneal cavity of a new group of mice and again observe no ill effects.  During a third experiment, they inject live strain A bacteria in combination with the killed strain B lysate, resulting in death of the mice.  Which of the following genetic processes most likely accounts for the observed findings of these experiments?

Quizplus · Accepted Answer

11ec160b_386c_fa53_9249_f319f92b3947_MD0001_00 Certain strains of Streptococcus pneumoniae express capsular polysaccharides that inhibit phagocytosis, making it a successful pathogen. Strains lacking the capsule are not pathogenic; however, S pneumoniae is able to obtain new genetic material from the environment that is released following the death and lysis of neighboring bacterial cells. This process, known as transformation, allows the bacterium to take up exogenous DNA fragments, integrate the DNA into its genome, and express the encoded proteins. Through this method, nonvirulent strains of S pneumoniae that do not form a capsule can acquire the genes that code for the capsule and therefore gain virulence. Bacteria that have the innate capacity to undergo transformation are said to be naturally competent and include Haemophilus, Streptococcus, Bacillus, and Neisseria species. (Choice B) In transduction, a bacteriophage (virus) transfers DNA from one bacterial cell to another. While replicating within a host bacterium, a bacteriophage may accidentally incorporate host bacterial DNA into the phage particle. Once released, it can then transfer DNA from the previous host into a newly infected bacterium. By this mechanism, bacteria can acquire genes for virulence and antibiotic resistance. (Choice C) Conjugation is a form of one-way DNA transfer performed by bacteria carrying a plasmid with the fertility (F) factor. The process begins with the donating bacterium producing a sex pilus, which then forms a direct connection with the receiving bacterium. Next, the donating bacterium transfers a single DNA strand containing the F factor to the recipient organism, after which, complementary DNA strands are synthesized. (Choice D) Spontaneous or induced mutations change the nucleotide sequence of a gene, potentially altering the amino acid sequence of the protein product. Through this mechanism, bacteria form novel proteins with potentially useful functions to aid with survival. (Choice E) Transposons are mobile genetic elements that can mediate DNA transfer from plasmids to a bacterial chromosome, move genetic material from one position to another along a bacterial chromosome, or transfer genes from a bacterial chromosome to a plasmid. The location of a gene in the genome is important as it determines its proximity to promoter or suppressor regions. Educational objective: Streptococcus pneumoniae is able to undergo transformation, which allows the bacterium to take up exogenous DNA fragments and express the encoded proteins. Through this method, strains of S pneumoniae that do not form a capsule can acquire the genes that code for the capsule and therefore gain virulence.

Microbiology Researchers Conduct a Series of Experiments to Determine How