The natural history of a biocrust architect, the cyanobacterium Microcoleus vaginatus

Abstract The filamentous cyanobacterium Microcoleus vaginatus is a pioneer soil colonizer and the most important microorganism for the formation of cyanobacterial biological soil crusts (or biocrusts), biofilm-like communities developing on soil surfaces exposed to light that become prominent in arid and polar lands. Among the most abundant cyanobacteria by global biomass, it contributes significantly through its biocrust-building to the global terrestrial carbon and nitrogen cycles. Locally, it contributes to the fertility and stability against erosion of the soils it inhabits and has become an indispensable tool in arid soil restoration efforts. Despite its importance, it remains relatively understudied. Because most work has been descriptive and ecological in nature, the knowledge amassed could be called a natural history. We provide an integrative review of what is known about its biology, what is not, and what is hindering advancement. We touch on its evolutionary history and population genetics, its physiological, genetic (genomic), behavioral, and ecological capacities, including some that present apparent paradoxes. We also explore the consequential relationships it keeps with other microbes, both mutualistic and antagonistic. The different aspects are guided by a dual leitmotiv to understand its ecological success and environmental impact, and to predict its fate in a changing world.