Desert Crusts

Abstract

A significant fraction of the world's land surface is covered by arid and semiarid land. Desert crusts, microbial communities formed from cyanobacteria, algae, fungi, and bacteria, are important ecosystems that stabilize and enrich desert soils. Cyanobacteria are key players, often providing physical cohesion, primary production, and life-supporting nitrogen fixation. Here the overall structure of crusts, the important microbial partners, and the microbial diversity that is present are discussed. Some of the special features of these communities and the individual organisms are their tolerances to desiccation and to high levels of UV radiation. Mechanisms to survive long periods of severe dehydration include the synthesis of large amounts of trehalose and the excretion of copious quantities of unique exopolysaccharides. Adaptations that allow survival in spite of high levels of UV radiation include mobility and the synthesis of natural sunscreens, scytonemin, and mycosporines. Much remains to be learned about these ubiquitous microbial consortia, whose functionalities and interrelationships are beginning to be probed at the molecular level. This chapter reviews the general microbial aspects of desert crusts and gives a special emphasis to the involvement of cyanobacteria.