Bacteria Y, with 17% adenine and a higher guanine-cytosine content, is likely the thermophilic bacterium, as the higher GC pairs offer greater stability under elevated temperatures.
In the DNA samples from bacteria X and Y, the relative proportions of adenine, guanine, thymine, and cytosine are determined by Chargaff's rules. Assuming equal pairing of A-T and G-C, we can infer that the percentages of thymine and cytosine mirror those of adenine and guanine, respectively. Therefore, for bacteria X (32% adenine), the approximate composition would be A = 32%, T = 32%, G = 18%, C = 18%.
Similarly, for bacteria Y (17% adenine), the composition would be A = 17%, T = 17%, G = 33%, C = 33%. The assumption is based on the principle of base-pairing in DNA. Given that one of these bacteria was isolated from a hot spring, the higher temperature suggests thermophilic adaptations. Therefore, the species with a higher guanine-cytosine (GC) content, bacteria Y, is more likely the thermophilic bacterium, as GC pairs are more stable under elevated temperatures.