ABSTRACT

Extreme environments such as glaciers, hot springs, caves, deserts, and deep seas are habitats with special classes of organisms, generally termed extremophiles. To classify an organism as an extremophile, the preferred growth conditions must be outside the range of the optimal growth parameters of Escherichia coli (37 °C, pH 7.4, salinity 0.9%–3%, and 1 atm).1 Thus, extremophiles comprise several major classes dependent upon the environments in which they tolerate or achieve optimal growth, including psychrophiles (temperatures below 15 °C), thermophiles (temperatures above 50 °C), barophiles (high pressure), halophiles (high salt concentration), acidophiles (low pH conditions), and xerophiles (low water).1 Additional classes of extremophiles include organisms that live in low light conditions (e.g., caves), also known as photophobic organisms, and those that live in toxic environments (e.g., Superfund sites).2,3 There are also organisms that tolerate more than one

CONTENTS

12.1 Introduction .......................................................................................................................... 341 12.2 Psychrophiles and Psychrotolerant Organisms ..................................................................... 342

12.2.1 Corals ........................................................................................................................ 343 12.2.2 Sponges .....................................................................................................................344 12.2.3 Tunicates ................................................................................................................... 349 12.2.4 Bacteria ..................................................................................................................... 352

12.3 Thermophiles ........................................................................................................................ 358 12.4 Barophiles .............................................................................................................................360 12.5 Halophiles ............................................................................................................................. 362 12.6 Acidophiles ...........................................................................................................................366