Adaptive response

The adaptive response is a DNA damage response pathway prevalent across bacteria that protects DNA from damage by external agents or by errors during replication.^[1][2] It is initiated specifically against alkylation, particularly methylation, of guanine or thymine nucleotides or phosphate groups on the sugar-phosphate backbone of DNA. Under sustained exposure to low-level treatment with alkylating mutagens, bacteria can adapt to the presence of the mutagen, rendering subsequent treatment with high doses of the same agent less effective.^[3][4]

Environmental influence plays a crucial role in the developmental plasticity of genotypes due to the introduction of DNA damaging agents. This phenomenon and the defense mechanism that has evolved to protect an organism’s genotype against damage and prevent multiple phenotypes is known as the adaptive response.^[5] Since the adaptive response is able to prevent the possibility of different phenotypes it, therefore, allows organisms to minimize the stress effects it experiences from different stressors and eventually develop a resistance to the stressors.^[5] The effects of various chemical, biological, and physical genotoxic damaging agents jeopardize the genotypic integrity of all organisms; however, many evolutionary defense mechanisms have developed so that the stressors stimulate the adaptive response to reduce the stress to a more reasonable and manageable level and reduce genetic damage. ^[2]

Many of these defense mechanisms have contributed to the nonspecific adaptive response by "conditioning" the effected organisms with small amounts of particular stressors to stimulate cellular conformation changes and increase the resistance when the organism is exposed to higher concentrations of that particular stressor. For example, the decomposition of water produces highly reactive hydroxyl free radicals that can damage DNA, therefore, stimulating DNA repair mechanisms.^[5] This DNA up-regulation is involved in the adaptive response because the organism is being conditioned to protect itself against these stressors. Reactive oxygen species (ROS) are very damaging to DNA and highly associated with the adaptive response. When free radicals attack the important biomolecules that makeup organisms, harmful molecular intermediates react with and damage DNA leading to base damage or breaks in the dsDNA strand. The adaptive response is helpful to prevent damage and maintain the integrity of the genome.^{[citation needed]}