Major Compatible Solutes and Structural Adaptation of Proteins in Extremophiles

Introduction

Over the previous decades, the scientific community had explored various extreme environments for the hunt of microorganisms that can thrive in them. Because of their ability to sustain life in extreme habitats, these microorganisms are entitled extremophiles. Extremophiles can be considered as an important key to the evolutionary history on earth since such habitats are existing on earth from the time of evolution. These organisms can survive in extreme hot niches, acidic, alkaline, salt solutions, and ice whereas some have the unique ability to grow in toxic waste (Alavi et al., 2020), organic solvents (Isken & de Bont, 1998), and heavy metals (Alavi et al., 2020). Extreme conditions mentioned above are intolerable for other earthly life-forms. The word 'extreme' in itself implies that they are capable of growing and surviving in uncommon conditions. These microorganisms utilize various strategies for adaptation to extreme habitats. Proteins and other molecules of extremophilic microorganisms can be great resources for mankind with unique biotechnological importance (Raddadi et al., 2015). The organisms are categorized as extremotolerant and extremophiles which indicates that former organisms can tolerate extreme environments while later love such harsh conditions respectively (Verma et al., 2020).

Most of these organisms fall under the domain of Bacteria and Archaea. This includes those that love the extremely high temperature and extremely low temperature known as Thermo/Hyperthermophiles and psychrophiles respectively, those that survive in high pH and low pH termed as Acidophiles and Alkalophiles respectively, organisms survive in high salt concentration known as Halophiles, those that thrive at high atmospheric pressure called barophiles and organisms which can withstand a high level of toxic agents are termed, toxitolerants (Rampelotto, 2013). As physicochemical parameters can be extremely high where these microorganisms are capable to live, they are also called polyextremophiles (Chela-Flores, 2013). A common example of polyextremophiles is thermoacidophiles which can survive in extremely high temperatures as well as they require acidic pH for survival. In addition to being extremely alkaline and acidic simultaneously, many hot springs are rich in metal content. Several hypersaline lakes are extremely alkaline, while the deep oceans are usually cold and oligotrophic (very low nutrient content) and exposed to high pressure (Strazzulli et al., 2020).