The thermostable DNA polymerase is isolated from the bacterium:

The correct answer is Option (3) → Thermus aquaticus

PCR runs through a very high temperature in every cycle to separate the DNA strands. So it needs a thermostable DNA polymerase. The bacterium that gives this enzyme lives in hot springs, and the enzyme is called Taq polymerase after it.

Option (1) Thermus marinus — Incorrect. This is not the source of the thermostable DNA polymerase. Only the first word matches. “Marinus” means “of the sea”, while the source of Taq polymerase is a bacterium of hot water.

Option (2) Thermus thermotoga — Incorrect. This is not the source either. Thermotoga is the name of a separate genus of heat-loving bacteria, so it is not a species of Thermus.

Option (3) Thermus aquaticus — Correct. It is the source of the thermostable DNA polymerase. The “T” and “aq” of its name give the enzyme the name Taq.

Option (4) Thermus aquifeticus — Incorrect. The second word is close to “aquaticus” but changed. The bacterium used for PCR is Thermus aquaticus.

Note: A similar question was also asked in CUET (UG) 2026 on 06-06-2026 (Slot 1), in CUET (UG) 2025 on 20-05-2025 (Slot 2), and in CUET (UG) 2024 on 29-05-2024 (Slot 1).

NCERT Extract:
Amplification of Gene of Interest Using PCR – “… PCR stands for Polymerase Chain Reaction. In this reaction, multiple copies of the gene (or DNA) of interest is synthesised in vitro using two sets of primers (small chemically synthesised oligonucleotides that are complementary to the regions of DNA) and the enzyme DNA polymerase. The enzyme extends the primers using the nucleotides provided in the reaction and the genomic DNA as template. If the process of replication of DNA is repeated many times, the segment of DNA can be amplified to approximately billion times, i.e., 1 billion copies are made. Such repeated amplification is achieved by the use of a thermostable DNA polymerase (isolated from a bacterium, Thermus aquaticus), which remain active during the high temperature induced denaturation of double stranded DNA.”