Concept explainers
A constitutive mutant is a strain that continuously makes a protein that is inducible in the wild type. Describe two ways in which a change in a DNA molecule could lead to the emergence of a constitutive mutant. How could these two types of constitutive mutants be distinguished genetically?
To discuss:
A constitutive mutant (a strain) can continuously produce a protein molecule that is inducible in the wild type. Describe two ways to produce a constitutive mutant through DNA change. How these two types of constitutive mutants are differentiated genetically.
Concept introduction:
A mutant strain can continuously synthesize a protein because of a mutation in the regulatory gene is known as a constitutive mutant. The regulatory gene is always expressed or not switched off. A strain with a mutation in the lac operon is an example of a constitutive mutant. The lac operon mutation can lead to the transcription of the lac genes in the absence of lactose in the medium.
Explanation of Solution
Formation of a constitutive mutant:
- A constitutive mutant can be produced if the altered repressor protein not able to recognize the operator due to mutation.
- A constitutive mutant can be produced if an operator locus not able to interact with the normal repressor due to mutation.
In both cases, the mutation can lead to continuous production of the protein. The two constitutive mutants can be differentiated genetically by the cis-trans test or a complementation test in merodiploid cells. This test is used to find whether the mutations found in the two mutant strains are in different genes or not.
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Chapter 11 Solutions
Brock Biology of Microorganisms (15th Edition)
- Transposon mutagenesis was used to generate a library of mutants within the Salmonella genome. You are trying to identify a colony with the transposon inserted in the pathogenic related gene SPI-1 using PCR. Forward and reverse primers are generated that flank either side of the gene and yield a wild type product that is 900 bases in length. Which of the colonies sampled in the gel would you expect to contain the SPI-1 gene with transposon insertion? 3,000 2,000 1,000 700 500 300 100 Ladder Colony A Colony B Colony C Colony D Colony E none colonies A&C colonies B&E O colonies A, C, &D colonies B, D, &E -arrow_forwardBacteriophage P22 was used in generalised transduction experiments to infect the Salmonella typhimurium donor strains described in the table below. The resulting phage lysates were then used to infect the recipient strains of S. typhimurium recipient strains listed in the table. In each cross, a phenotype was selected for one of the selected for one of the three genetic markers studied (str, aceA, thrA), and were made to select the recombinants corresponding to the other two markers. markers. The results are given in the following table: Strain I donor str thrA aceA thrA str aceA+ Strain recipient strs thrA+ aceA thrA str aceA Phenotype selected Str Ace+ Str recombinants selected ThrA ThrA ThrA ThrA Ace Ace Number 60 40 95 5 10 90 str: gene involved in streptomycin resistance, aceA: gene involved in the use of acetate as a carbon source, thrA: gene involved in threonine biosynthesis. 1) What are the selective media used in these three transduction experiments? to obtain the selected…arrow_forwardA research group is studying a bacterium X that binds to mucosal cells in the lung and invades. Wildtype X has an LD50 value of 10 bacteria when administered to mice by inhalation. Using transposon mutagenesis, the researchers have isolated two mutants of X that they call Xmut1 and Xmut2, both of which have LD50 values of 105 when inhaled by mice. However, in tissue culture cells, Xmut1 can invade the cells just as well as wild-type X, while Xmut2 cannot. Provide a possible explanation for these results.arrow_forward
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- A bacterial transformation is performed with a donor strain that is resistant to four drugs, A, B, C, and D, and a recipient strain that is sensitive to all four drugs. The resulting recipient cell population is divided and plated onmedia containing various combinations of the drugs. The following table shows the results.a. One of the genes is distant from the other three, which appear to be closely linked. Which is the distant gene? b. What is the likely order of the three closely linked genesarrow_forwardConsider the following types of cells: F+, F-, Hfr, and F’ cells. Which of these four types of cells are capable of acting as a donor during conjugation? What genes does each cell that is capable of acting as a donor donate to the recipient cell?arrow_forwardT. Miyake and M. Demerec examined proline-requiring mutations in the bacterium Salmonella typhimurium (). On the basis of complementation testing, they found four proline auxotrophs: proA, proB, proC, and proD. To determine whether proA, proB, proC, and proD loci were located close together on the bacterial chromosome, they conducted a transduction experiment. Bacterial strains that were proC+ and had mutations at proA, proB, or proD were used as donors. The donors were infected with bacteriophages, and progeny phages were allowed to infect recipient bacteria with genotype proC− proA+ proB+ proD+. The recipient bacteria werethen plated on a selective medium that allowed only proC+ bacteria to grow. After this, the proC+ transductants were plated on selective media to reveal their genotypes at the other three pro loci. The following results were obtained: Q.Why are there no proC− genotypes among the transductants?arrow_forward
- T. Miyake and M. Demerec examined proline-requiring mutations in the bacterium Salmonella typhimurium (). On the basis of complementation testing, they found four proline auxotrophs: proA, proB, proC, and proD. To determine whether proA, proB, proC, and proD loci were located close together on the bacterial chromosome, they conducted a transduction experiment. Bacterial strains that were proC+ and had mutations at proA, proB, or proD were used as donors. The donors were infected with bacteriophages, and progeny phages were allowed to infect recipient bacteria with genotype proC− proA+ proB+ proD+. The recipient bacteria werethen plated on a selective medium that allowed only proC+ bacteria to grow. After this, the proC+ transductants were plated on selective media to reveal their genotypes at the other three pro loci. The following results were obtained: Q.Which genotypes represent single transductants and which represent cotransductants?arrow_forwardT. Miyake and M. Demerec examined proline-requiring mutations in the bacterium Salmonella typhimurium (). On the basis of complementation testing, they found four proline auxotrophs: proA, proB, proC, and proD. To determine whether proA, proB, proC, and proD loci were located close together on the bacterial chromosome, they conducted a transduction experiment. Bacterial strains that were proC+ and had mutations at proA, proB, or proD were used as donors. The donors were infected with bacteriophages, and progeny phages were allowed to infect recipient bacteria with genotype proC− proA+ proB+ proD+. The recipient bacteria werethen plated on a selective medium that allowed only proC+ bacteria to grow. After this, the proC+ transductants were plated on selective media to reveal their genotypes at the other three pro loci. The following results were obtained: Q.Is there evidence that proA, proB, and proD are located close to proC? Explain your answer.arrow_forwardE. coli strains diploid for the lac region were constructed by introducing a plasmid carrying the lac genes. The plasmid carries one copy of the lac region, and the chromosome carries the other copy. The two copies of the lac region have different genotypes, as shown in the chart below. Indicate whether the products of the lacy gene (permease) and the lacZ gene (B-galactosidase) will be inducible, uninducible, or constitutive in each strain (assuming glucose is absent). lac region on plasmid lac region on chromosome permease B-galactosidase I-o+Z+Y- I+o+ Z-Y+ I+o+Z+Y- I+o° Z=Y+ I- oº Z+Y- I+o+ Z-Y+ Is o+ Z+Y- I+o+ Z-Y+ I+ oc Z+Y- IS O+ Z-Y+arrow_forward
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