THE ROLE OF ENERGETICS IN ACCLIMATION AND ADAPTATION TO ENVIRONMENTAL EXTREMES

For any organism, its presence and success depend upon the complex of environmental conditions. Environmental extremes include physical or chemical parameters that are low, high or highly variable. The key to whether an organism can survive and even thrive in an extreme environment is related to energetics, which function at both the acclimation (individual) and adaptation (evolutionary) levels. With physical extremes, the key to survival and ecological/evolutionary success is the ability to synthesize organic molecules (e.g., enzymes, proteins, nucleic acids) that maintain functionality under conditions (e.g., temperature, pressure, ultraviolet radiation) at which such molecules typically cannot function. Chemical extremes pose a somewhat different set of challenges. Some elements are biologically essential at low concentrations, yet toxic at elevated concentrations. Accessing essential elements at low concentrations clearly requires energy expenditure. Tolerating chemical excess also requires energy, frequently involving production of molecules that bind with toxic chemicals, enabling them to be sequestered, inactivated or excreted. Thus, the ultimate limiting resource for an organism is energy. Does the organism have access to sufficient energy not only to survive the environmental conditions, but also to grow and reproduce? To survive extremes does not require perfect adaptation, just that the organism be sufficiently adapted either to out compete other organisms for energy sources or to survive where they cannot. Furthermore, the organism does not need to grow and reproduce during the most extreme conditions, but may survive by producing resistant, dormant stages. Symbioses are another common strategy associated with adapting to extremes. Foraminifers and other fossilizable protists typically cannot survive the environmental extremes occupied by prokaryotes. Nevertheless, protists can provide lessons as to how eukaryotic cells function under environmental extremes. Although utilized as paleoenvironmental indicators for nearly a century, foraminifers and other protists are increasingly being used as bioindicators in environmental research. Better understanding of their molecular and physiological responses to environmental extremes will enhance both applications.