Lithic cyanobacterial communities in the polyextreme Sahara Desert: implications for the search for the limits of life

• Published in: Environmental microbiology Vol. 24; no. 1; pp. 451 - 474
• Main Authors: Mehda, Smail, Muñoz‐Martín, M. Ángeles, Oustani, Mabrouka, Hamdi‐Aïssa, Baelhadj, Perona, Elvira, Mateo, Pilar
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01-01-2022; Wiley Subscription Services, Inc
• Subjects: Africa; Astrobiology; Bio-assays; Bioassays; Colonization; Community composition; Cyanobacteria; Cyanobacteria - physiology; Desert Climate; Deserts; Desiccation; Ecosystem; Environmental conditions; Hot Temperature; Lithic; Microorganisms; Moisture availability; Soil Microbiology; Stone; Temperature tolerance; Africa; Sahara Desert
• ISSN: 1462-2912; 1462-2920
• DOI: 10.1111/1462-2920.15850

Summary
The hyperarid Sahara Desert presents extreme and persistent dry conditions with a limited number of hours during which the moisture availability, temperature and light allow phototrophic growth. Some cyanobacteria can live in these hostile conditions by seeking refuge under (hypolithic) or inside (endolithic) rocks, by colonizing porous spaces (cryptoendoliths) or fissures in stones (chasmoendoliths). Chroococcidiopsis spp. have been reported as the dominant or even the only phototrophs in these hot desert lithic communities. However, the results of this study reveal the high diversity of and variability in cyanobacteria among the sampled habitats in the Sahara Desert. The chasmoendolithic samples presented high coccoid cyanobacteria abundances, although the dominant cyanobacteria were distinct among different locations. A high predominance of a newly described cyanobacterium, Pseudoacaryochloris sahariense, was found in hard, compact, and more opaque stones with cryptoendolithic colonization. On the other hand, the hypolithic samples were dominated by filamentous, non‐heterocystous cyanobacteria. Thermophysiological bioassays confirmed desiccation and extreme temperature tolerance as drivers in the cyanobacterial community composition of these lithic niches. The results of the present study provide key factors for understanding life strategies under polyextreme environmental conditions. The isolated strains, especially the newly described cyanobacterium P. sahariense, might represent suitable microorganisms in astrobiology studies aimed at investigating the limits of life.