Corien Bakermans - Microbial Evolution under Extreme Conditions

Extreme environments generally have physicochemical conditions that are challenging to cells and their macromolecules ( .) Environments with physicochemical extremes (i.e. pH or temperature) are considered in this volume, as well as environments with extremely low nutrient concentrations ( Chapter 7) and extraordinary cell-cell interactions (symbiosis, Chapter 12). Most of the extreme conditions examined occur in the natural (versus human created) world; however, anthropogenic environments such as acid mine drainage (AMD, Chapter 2) and extreme conditions that occur in our homes (such as extreme heat of dishwashers, extreme dryness, and variations therein) are included ( Chapter 10).

. Characteristics of extreme environments.

The organisms that inhabit extreme environments are called extremophiles because they thrive in the physicochemical conditions of extreme environments. These extremophiles can be found in all three domains (Archaea, Bacteria, and Eukaryota), although sometimes with a limited phylogenetic distribution. Some extremophiles are polyextremophiles ( Chapters 8 and 10) that thrive in multiple extreme conditions (e.g. high temperature, pH, and salt concentrations polyextremotolerant (i.e. tolerating, but not thriving in, the extreme conditions). While extremophiles succeed in extreme environments, the challenges presented by the physicochemical conditions of extreme environments commonly manifest as a lower abundance and diversity of inhabitants. For example, diversity decreases with increasing and Chapter 4).

With their relatively limited numbers of inhabitants, extreme environments can serve as good model systems for the study of evolutionary processes , helping to reduce the need for cultivation. Extreme environments often have fewer physicochemical variables in the sense that one condition (such as pH or temperature) may dominate, thereby reducing variability in the system.

Extreme environments are also good models seeing as their geographic boundaries, and often their geological history, can be mapped. The history and distribution of extreme environments will affect the evolutionary history of extremophiles (and their adaptive traits). For example, currently high temperature (hydrothermal) systems are relatively isolated from one another geographically, yet plate tectonics and volcanism have insured that high temperature environments, which likely dominated the early earth ( Chapter 9), have existed throughout earths history and alkaliphiles may be ancient and could have lots of interactions with other acidophiles and alkaliphiles .

All of these factors allow extreme environments to serve as model systems. Ecosystems with a dominant species or physicochemical condition can be very useful for disentangling the effects of different factors on the processes and mechanisms of microbial evolution. In particular, the variety of extreme environments, and especially comparisons between environments, will further facilitate the examination of microbial evolution and evolutionary processes across an entire spectrum of conditions from low to high diversity, low to high cell density, and low to high variability of physicochemical or biological conditions.