The composition of endolithic communities in gypcrete is determined by the specific microhabitat architecture

Abstract

Abstract. Endolithic microhabitats have been described as the last refuge for life in arid and hyper-arid deserts where life has to deal with harsh environmental conditions. A number of rock substrates from the hyper-arid Atacama Desert, colonized by endolithic microbial communities such as halite, gypsum crusts, gypcrete, calcite, granite and ignimbrite, have been characterized and compared using different approaches. In this work, three different endolithic microhabitats are described, each one with a particular origin and architecture, found within a lithic substrate known as gypcrete. Gypcrete, an evaporitic rock mainly composed of gypsum (CaSO4 ⋅ 2H2O) and collected in the Cordón de Lila area of the desert (Preandean Atacama Desert), was found to harbour cryptoendolithic (within pore spaces in the rock), chasmoendolithic (within cracks and fissures) and hypoendolithic (within microcave-like pores in the bottom layer of rock) microhabitats. A combination of microscopy investigation and high-throughput sequencing approaches were used to characterize the endolithic communities and their habitats at the microscale within the same piece of gypcrete. Microscopy techniques revealed differences in the architecture of the endolithic microhabitats and the distribution of the microorganisms within those microhabitats. Cyanobacteria and Proteobacteria were dominant in the endolithic communities, of which the hypoendolithic community was the least diverse and hosted unique taxa, as a result of less access to sun radiation. These results show, for the first time, that the differences in the architecture of a microhabitat, even within the same piece of a lithic substrate, play an essential role in shaping the diversity and composition of endolithic microbial communities.

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

“…Although Chroococcidiopsis is the dominant cyanobacterium in endolithic habitats in hot deserts, such as the Atacama (Dong et al ., 2007; Crits‐Christoph et al ., 2016; Meslier et al ., 2018; Ertekin et al ., 2020; Qu et al ., 2020; Casero et al ., 2021), Negev (Israel) and Namib (southern Africa) Deserts (Qu et al ., 2020), other coccoid taxa have also been found in endolithic assemblages from the Atacama Desert, such as Gloeocapsa (Crits‐Christoph et al ., 2016; Ertekin et al ., 2020. ; Casero et al ., 2021) and Halothece (Ertekin et al ., 2020).…”

“…Recent culture‐dependent and culture‐independent studies, also in the Atacama Desert, have shown the occurrence of Synechococcus , Gloeocapsopsis (Casero et al ., 2021), Aliterella , and Pleurocapsa minor (Jung et al ., 2019). In addition, the filamentous, non‐heterocystous Trichocoleus sociatus and the heterocystous S. hyalinum (Jung et al ., 2019) and Calothrix and Fischerella (Casero et al ., 2021) were also found. However, clear differences were found in polar deserts with increased abundances of filamentous, non‐heterocystous cyanobacteria, such as Phormidium (Qu et al ., 2020; Khomutovska et al ., 2021a, 2021b), Leptolyngbya , and Nodosilinea (Rego et al ., 2019; Khomutovska et al ., 2021a, 2021b).…”

“…These differences can be related to the distinct characteristics of the rocks at this sampling location, since the climatic conditions were similar to those of the MAS and SIK locations, all of which are close in vicinity (approximately 80 km among them) in the Ouargla region. Substrates have been found to be a key factor in shaping the diversity and composition of endolithic cyanobacterial communities, principally due to their specific microhabitat architecture, which can vary depending on internal structural elements such as the porosity (which is often directly related to the water retention capacity of the substrate), light transparency, and/or light‐scattering properties of substrates (Wierzchos et al ., 2015; Meslier et al ., 2018; Wierzchos et al ., 2018; Ertekin et al ., 2020; Casero et al ., 2021). In this sense, we found that the rock samples at the PLM location were very hard, compact, and more opaque than those in the other locations, allowing less access to solar radiation; this feature can clearly condition colonization and therefore account for the lower diversity and specific cyanobacterial community.…”

Algal Toxic Compounds and Their Aeroterrestrial, Airborne and other Extremophilic Producers with Attention to Soil and Plant Contamination: A Review

“…Endolithic algae inhabit the inner surfaces or fissures of stones and rocks and comprise a very specific community, which after the pioneer works by Imre Friedmann and his colleagues (e.g., [276][277][278][279] is considered extremophilic [7,280,281]. Nevertheless, little is known about the global biodiversity of algal endoliths, but despite some fine-scale partitioning depending on the rock types and local climate conditions, the similarity in species composition allows to generalize that cyanoprokaryotes, and the polyextremophilic BMAA producing [126] genus Chroococcidiopsis in particular, often dominates [4, 13,[280][281][282][283][284][285][286][287]. Among all recorded endolithic algae, occur other genera, from which toxigenic species have been found in different, mainly aquatic habitats: Anabaena, Aphanocapsa, Lyngbya, Phormidium and Plectonema (e.g., [276][277][278][279]284,[287][288][289][290][291][292][293][294][295]) (Table 1).…”

“…The unicellular coccal cyanoprokaryote Synechocystis sp PCC68034 is able to accumulate large concentrations of Mn 2+ [13]. The IR-resistance in the coccal cyanoprokaryote Chroococcidiopsis from desert and hypersaline environments possibly reflects its ability a to survive prolonged desiccation due to its thick protective mucilaginous (extracellular polysaccharide) envelopes and intracellular trehalose accumulation, as well as through efficient repair of the DNA damage that accumulates during dehydration [283,285,286]. There are no targeted toxin investigations on these radioresistant strains, but both genera have been reported as cyanotoxin producers [73,126] (Table 1).…”