54. DNA isolated from four unidentified species of bacteria – A, B, C and D has been estimated to
have 38%, 26%, 24% and 12% thymine, respectively. One of these four species was isolated from a
hot spring (64°𝐶). Identify the candidate which is most likely to be a thermophilic bacterium.
A. A
B. B
C. C
D. D

Introduction:

Thermophilic bacteria are organisms that thrive in high-temperature environments, such as hot springs, hydrothermal vents, and deep-sea geothermal systems. These bacteria are adapted to withstand extreme conditions, and one of the primary ways they do this is by having a unique DNA structure. A key feature of thermophilic bacteria is the GC content of their DNA, which influences the stability of their DNA at higher temperatures.

In this article, we will explore how the DNA composition, particularly the thymine content, can help us identify which of the four bacterial species—A, B, C, or D—is most likely to be thermophilic.

Understanding DNA Composition and Temperature Adaptation:

The DNA of all living organisms is made up of four nucleotides: adenine (A), thymine (T), cytosine (C), and guanine (G). The base pairing rules state that adenine pairs with thymine (A-T), and cytosine pairs with guanine (C-G). The stability of the DNA molecule depends on the GC content; the higher the GC content, the more stable the DNA is at higher temperatures because the C-G bonds are held together by three hydrogen bonds, compared to the two hydrogen bonds between A-T pairs.

Thermophilic organisms tend to have a higher GC content to ensure the stability of their DNA at high temperatures. Therefore, we can deduce the nature of the species isolated from a hot spring based on the thymine content, since thymine is paired with adenine (T-A), and a lower thymine content suggests a relatively higher proportion of GC pairs.

The DNA Composition of the Bacterial Species:

Let’s analyze the thymine content of the four bacterial species:

1. Species A: 38% thymine

   • This suggests a lower GC content since A pairs with T. A lower GC content makes the DNA less stable at higher temperatures.

2. Species B: 26% thymine

   • With a lower thymine content, this species likely has a higher GC content. This could indicate better stability at higher temperatures, making it a good candidate for thermophilic adaptation.

3. Species C: 24% thymine

   • Similar to species B, the lower thymine content points to a higher GC content, suggesting thermophilic characteristics.

4. Species D: 12% thymine

   • This species has the lowest thymine content, suggesting the highest GC content among the four. This would provide maximum stability in high-temperature environments.

Conclusion:

The species with the lowest thymine content, which suggests the highest GC content, is Species D. Given the temperature conditions of a hot spring, Species D is the most likely candidate for being a thermophilic bacterium.

Answer:

D. D

For further insights on bacterial adaptations and DNA composition, check out the following resources: