Microenvironmental Conditions Drive the Differential Cyanobacterial Community Composition of Biocrusts from the Sahara Desert

Abstract

The Sahara Desert is characterized by extreme environmental conditions, which are a unique challenge for life. Cyanobacteria are key players in the colonization of bare soils and form assemblages with other microorganisms in the top millimetres, establishing biological soil crusts (biocrusts) that cover most soil surfaces in deserts, which have important roles in the functioning of drylands. However, knowledge of biocrusts from these extreme environments is limited. Therefore, to study cyanobacterial community composition in biocrusts from the Sahara Desert, we utilized a combination of methodologies in which taxonomic assignation, for next-generation sequencing of soil samples, was based on phylogenetic analysis (16S rRNA gene) in parallel with morphological identification of cyanobacteria in natural samples and isolates from certain locations. Two close locations that differed in microenvironmental conditions were analysed. One was a dry salt lake (a “chott”), and the other was an extension of sandy, slightly saline soil. Differences in cyanobacterial composition between the sites were found, with a clear dominance of Microcoleus spp. in the less saline site, while the chott presented a high abundance of heterocystous cyanobacteria as well as the filamentous non-heterocystous Pseudophormidium sp. and the unicellular cf. Acaryochloris. The cyanobacteria found in our study area, such as Microcoleus steenstrupii, Microcoleus vaginatus, Scytonema hyalinum, Tolypothrix distorta, and Calothrix sp., are also widely distributed in other geographic locations around the world, where the conditions are less severe. Our results, therefore, indicated that some cyanobacteria can cope with polyextreme conditions, as confirmed by bioassays, and can be considered extremotolerant, being able to live in a wide range of conditions.

Lipid Profiles From Fresh Biofilms Along a Temperature Gradient on a Hydrothermal Stream at El Tatio (Chilean Andes), as a Proxy for the Interpretation of Past and Present Biomarkers Beyond Earth

“…The 16S rRNA gene of cyanobacteria was amplified with the specific primer pairs CYA359F/CYA781Ra and CYA781Rb ( Nübel et al, 1997 ) in separate reactions. These specific cyanobacterial primers are widely used to identify cyanobacteria in different environments (e.g., Dorador et al, 2008 ; Azúa-Bustos et al, 2011 ; Mehda et al, 2021 ). Further information about the PCR conditions is available in the Supplementary Text 2 .…”

Tecnologías ómicas para la exploración de la biocostra del suelo

“…Los estudios centrados en abordar la problemática global de la degradación de los suelos se han enfrentado a que hoy en día muchos aspectos continúan desconocidos en lo que se ref iere al estudio y aprovechamiento de las comunidades microbianas de la biocostra, su diversidad aún resulta desconocida o se encuentra mal caracterizada, por lo que la identif icación y el seguimiento de las funciones que desempeñan los organismos que habitan la biocostra son los primeros pasos a considerarse (Mehda et al, 2021). En este sentido, el conocimiento del microbioma de las biocostras, sobre todo de aquellas de regiones geográf icas poco exploradas con condiciones ambientales extremas contribuye a la caracterización integral para la elaboración de propuestas que impacten en la restauración de los suelos degradados por procesos naturales y humanos (Giraldo-Silva, Nelson, Barger y Garcia, 2019).…”

“…Algunas de las funciones reportadas de estos microorganismos en las biocostras destacan sus estrategias de supervivencia a condiciones de desecación y radiación UV a través de la producción de enzimas y diversas moléculas implicadas en el mantenimiento y reparación celular, las cuales han sido reportadas gracias al desarrollo de las tecnologías ómicas (Wase et al, 2014;Shang et al, 2019). De igual forma, se realizó un estudio en el desierto del Sahara en el que se logró el aislamiento e identif icación morfológica y metagenómica de miembros que han sido encontrados en biocostras de diferentes localidades geográf icas (Microcoleus steenstrupii, Microcoleus vaginatus, Scytonema hyalinum, Tolypothrix distorta, Calothrix sp., entre otros); sin embargo, además de la identif icación, se realizó una evaluación de la resistencia al calor extremo y a la desecación, encontrando que la mayoría de las especies resisten temperaturas elevadas, y que además especies como S. hyalinum, M. steenstrupii, Pseudophormidium sp., N. commune y Nodosilinea muestran una resiliencia después de una etapa de rehidratación, lo que los convierte en candidatos potenciales para su evaluación in vivo como una alternativa de inoculación para evitar la degradación de los suelos (Mehda et al, 2021).…”

Bioactive Metabolites Produced by Cyanobacteria for Growth Adaptation and Their Pharmacological Properties

“…On the other hand, many cyanobacteria species form heterocysts, the cells that carry out atmospheric nitrogen fixation, especially during nitrogen deprivation [33]. This uniquely differentiated cell results in the dispersion of cyanobacterial genera in various ecosystems; for example, Anabaena and Trichodesmium inhabit open oceans, thermal springs and freshwaters [34,35], whereas Leptolynbya grows in geothermal springs, hot deserts, and surface crusts of semideserts [36,37].…”

“…Noteworthy, most filamentous cyanobacteria produce extracellular sheath as a method of adaptation, especially to water level fluctuation and high solute concentration, by providing a microenvironment for trichomes. For example, Microcoleus, Trichocoleus, Oscillatoria and some Schizothrix covered by thick sheath grow in saline soil crusts, semidesert regions, soil crusts of desert and polar environments [35,55,56]. However, some mat-forming Schizothrix and Oscillatoria enveloped by firm and thin sheaths inhabit diverse aquatic environments, freshwater, marine environments, thermal springs and polar water bodies [55].…”