Answer:

PCR (Polymerase Chain Reaction) is a widely used technique in molecular biology for amplifying a specific DNA sequence. One of the key components of PCR is the enzyme Taq polymerase, which is responsible for synthesizing new DNA strands during the amplification process.

The correct answer to the question is option 'B', which states that Taq polymerase is isolated from the bacterium Thermus aquaticus. This bacterium is a thermophilic microorganism found in hot springs and other thermal environments.

Explanation:

Taq polymerase is derived from Thermus aquaticus because this bacterium possesses a special DNA polymerase that is stable at high temperatures. In PCR, the reaction mixture is subjected to a series of temperature changes, including high heat denaturation (94-96°C) to separate the DNA strands and lower annealing temperatures (50-65°C) for the primers to bind to the target DNA.

Benefits of Taq polymerase from Thermus aquaticus:
- Heat stability: Taq polymerase is resistant to high temperatures, allowing it to withstand the denaturation step of PCR without becoming denatured itself.
- Optimal temperature: Taq polymerase works optimally at temperatures around 72°C, which is the temperature used in the extension step of PCR.
- Processivity: Taq polymerase has a high processivity, meaning that it can incorporate many nucleotides into the growing DNA strand before dissociating from the template.
- Purity: The isolation of Taq polymerase from Thermus aquaticus ensures that other bacterial contaminants are not present in the enzyme preparation.

Alternative options:
- Option 'A' (Agrobacterium tumefaciens) is incorrect because this bacterium is not known to produce Taq polymerase.
- Option 'C' (Streptomyces albus) is incorrect because Streptomyces species are not thermophilic, and their DNA polymerases are not suitable for PCR.
- Option 'D' (Escherichia coli) is incorrect because E. coli is a mesophilic bacterium and does not produce Taq polymerase.

In summary, Taq polymerase used in PCR is derived from Thermus aquaticus, a thermophilic bacterium that can withstand the high temperatures required for PCR amplification. Its heat stability, optimal temperature, and processivity make it an ideal enzyme for PCR.