Abstract
Extremophile microalgae have been categorized into six main categories that include thermophiles (able to tolerate high temperatures up to the boiling point of water), psychrophiles (capable of living in cold environments below the freezing point of water), barophiles (able to tolerate pressure as high as 1,000 atm), halophiles (capable of growing at salinities up to saturation state), acidophiles (thriving well at pH close to zero), and alkaliphiles (capable of growing at high pH > 10.0). In addition, some microalgal strains have developed mechanisms to thrive in an environment with multiple stress conditions that are collectively known as polyextremophiles. Here, we examine several microalgae that grow in a wide range of extremophilic conditions. Descriptions of the potential products synthesized by these exceptional microorganisms applied biotechnology is discussed. Examples of genetic and metabolic engineering already adapted in some extremophilic microalgae are also presented. The future direction and exploitation of extremophilic microalgae cultivated on a large scale are suggested.