Free-Living Amoebas in Extreme Environments: The True Survival in our Planet

Abstract

Free-living amoebas (FLAs) are microorganisms, unicellular protozoa widely distributed in nature and present in different environments, such as water or soil; they are maintained in ecosystems and play a fundamental role in the biological control of bacteria, other protozoa, and mushrooms. In particular circumstances, some can reach humans or animals, promoting several health complications. Notably, FLAs are characterized by a robust capacity to survive in extreme environments. However, currently, there is no updated information on the existence and distribution of this protozoan in inhospitable places. Undoubtedly, the cellular physiology of these protozoan microorganisms is very particular. They can resist and live in extreme environments due to their encysting capacity and tolerance to different osmolarities, temperatures, and other environmental factors, which give them excellent adaptative resistance. In this review, we summarized the most relevant evidence related to FLAs and the possible mechanism, which could explain their adaptative capacity to several extreme environments.

Figure 1

Free-living amoeba life cycle diagram. (a) Structure of the cyst, composed of three-layer: endocyst, mesocyst, and ectocyst. The presence of layer mesocyst is dependent on the genus. The trophozoite is the metabolically active vegetative form. (b) Diagram of environments where FLA can be found, created with http://BioRender.com/.

Figure 2

Taxonomic classification of free-living amoebas. The figure shows the taxonomic classification of the species corresponding to free-living amoebas. The figure was made based on the following authors [, , –108]), created with http://BioRender.com/.

Figure 3

Mechanism cyst amoeba biosynthesis. The figure shows the formation encystment process mechanism of the cyst's wall. The formation of the cyst wall is characterized by three major components: protein synthesis, cellulose, and galactose polymers, which affect the amoeba wall formation, created with http://BioRender.com/.