Final answer:
The high reversion rate of pond bacteria when exposed to base analogs suggests the spill contained mutagenic chemicals, potentially acting as base analogs. The Ames test could confirm this mutagenicity. The findings imply a rise in mutation risks for organisms in that environment.
Step-by-step explanation:
The bacteria from the pond showing an unusually high rate of mutation when treated with known mutagens, specifically base analogs such as 2-aminopurine, suggest that the chemicals in the spill might have mutagenic properties. This is evidenced by an increased rate of reversion, meaning that the original mutation induced by the chemical spill may be of a nature that is prone to correction in the presence of such mutagens.
The Ames test, commonly employed to assess mutagenicity, typically uses strains of bacteria that cannot synthesize a specific amino acid (e.g., histidine) due to a mutation. Exposure to a chemical suspect of causing mutations would increase the mutation rate, causing some bacteria to revert to being able to synthesize the amino acid.
Base analogs are known to be incorporated into DNA in place of the standard bases during replication, leading to mutations due to their different base-pairing properties. An increased reversion rate upon treatment with base analogs could mean that the original mutations might have involved base-pair substitutions that are prone to correction by these analogs. The chemical spill potentially contained substances with base analog-like properties, increasing the mutagenicity of affected bacteria in the pond.