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.

中文翻译：

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多极端撒哈拉沙漠中的石质蓝藻群落：对寻找生命极限的意义

极度干旱的撒哈拉沙漠呈现出极端和持续的干燥条件，在有限的几个小时内水分可用性、温度和光照允许光养生长。一些蓝细菌可以在这些恶劣的条件下生存，通过在（下质）或内部（内质）岩石下寻求庇护，通过在多孔空间（隐晶石）或石头中的裂缝（chasmoendoliths）中定居。球虫spp. 据报道，在这些炎热的沙漠岩石群落中，它们是主要的甚至是唯一的光养生物。然而，这项研究的结果揭示了撒哈拉沙漠采样栖息地中蓝藻的高度多样性和变异性。尽管主要的蓝藻在不同的位置是不同的，但 chasmoendolithic 样品呈现出高的球状蓝藻丰度。一种新描述的蓝细菌的高度优势，Pseudoacaryochloris sahariense, 在坚硬、致密和更不透明的结石中发现，并带有隐内石定植。另一方面，亚石样品以丝状、非杂囊蓝细菌为主。热生理生物测定证实干燥和极端温度耐受性是这些石质生态位的蓝藻群落组成的驱动因素。本研究的结果为理解多极端环境条件下的生命策略提供了关键因素。分离的菌株，尤其是新描述的蓝细菌P. sahariense，可能代表了旨在调查生命极限的天体生物学研究中合适的微生物。