The relevance of hormesis at higher levels of biological organization: Hormesis in microorganisms

Documented biphasic dose-responses date some 150 years back; however, massive evaluations of the occurrence of pollutant-induced hormesis, its quantitative characteristics, and the underlying mechanisms have been performed only in the recent years. One of the reasons why hormesis is not included in the ecological risk assessment may be its poorly explored relevance to levels of biological organization beyond the individual. Here, we summarize the highly reproducible occurrence of hormesis induced by various individual and combined chemicals in microorganisms, the hormetic response of bioluminescence, and the hormesis-based drug resistance. We also summarize key underlying mechanisms and discuss the relevance of hormesis in microorganisms-regulated organismic interactions, biological communication, and communities of microorganisms. Our exposition indicates the need for enhanced studies directed to reveal the implications of hormesis to levels of biological organization beyond the individual and that hormesis is considered in the ecological risk assessment.