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Microorganisms, in the most hyperarid deserts around the world, inhabit the inside of rocks as a survival strategy. Water is essential for life, and the ability of a rock substrate to retain water is essential for its habitability. Here we report the mechanism by which gypsum rocks from the Atacama Desert, Chile, provide water for its colonizing microorganisms. We show that the microorganisms can extract water of crystallization (i.e., structurally ordered) from the rock, inducing a phase transformation from gypsum (CaSO4·2H2O) to anhydrite (CaSO4). To investigate and validate the water extraction and phase transformation mechanisms found in the natural geological environment, we cultivated a cyanobacterium isolate on gypsum rock samples under controlled conditions. We found that the cyanobacteria attached onto high surface energy crystal planes ({011}) of gypsum samples generate a thin biofilm that induced mineral dissolution accompanied by water extraction. This process led to a phase transformation to an anhydrous calcium sulfate, anhydrite, which was formed via reprecipitation and subsequent attachment and alignment of nanocrystals. Results in this work not only shed light on how microorganisms can obtain water under severe xeric conditions but also provide insights into potential life in even more extreme environments, such as Mars, as well as offering strategies for advanced water storage methods.

In response to Wierzchos et al. (1) regarding the mechanism of water extraction from gypsum rock by desert colonizing microorganisms (2), we provide details that refute their incorrect assessments. We carefully selected areas without microorganism colonies that only contained gypsum, as confirmed by X-ray diffraction (XRD), for our culture experiments. Raman is useful for localized analysis of phase on surfaces, but here, it is complementary to XRD, which provides sample-wide detection (3, 4). Furthermore, selected area electron diffraction (SAED) confirms anhydrite, exhibiting arcs at 0.347 ± 0.003 nm and 0.278 ± 0.002 nm [(200) and (211) planes, respectively] with a [01−1] zone axis (Fig. 1 A and B ). The closest reflection for gypsum, the (130) plane, was not observed. SAED and fast Fourier transform (FFT) show twofold symmetry of the arcs, while the gypsum (130) plane exhibits fourfold symmetry, which was not observed. Finally, the crystal morphology of gypsum (monoclinic) was observably different from anhydrite (orthorhombic) (Fig. 1 C − F ). Thus, XRD, high-resolution … [↵][1]1To whom correspondence may be addressed. Email: david.k{at}uci.edu. [1]: #xref-corresp-1-1

Cyanobacteria are essential to microbial communities inhabiting translucent rocks in hyper-arid deserts. Metagenomic studies revealed unique adaptations of these cyanobacteria, but validation of the corresponding metabolic pathways remained challenging without access to isolates. Here, we present high-quality metagenome-assembled genomes for cyanobacteria, and their heterotrophic companions, isolated from endolithic substrates.

In hyper-arid deserts, endolithic microbial communities survive in the pore spaces and cracks of rocks, an environment that enhances water retention and filters UV radiation. The rock colonization zone is enriched in far-red light (FRL) and depleted in visible light. This poses a challenge to cyanobacteria, which are the primary producers of endolithic communities. Many species of cyanobacteria are capable of Far-Red Light Photoacclimation (FaRLiP), a process in which FRL induces the synthesis of specialized chlorophylls and remodeling of the photosynthetic apparatus, providing the ability to grow in FRL. While FaRLiP has been reported in cyanobacteria from various low-light environments, our understanding of light adaptations for endolithic cyanobacteria remains limited. Here, we demonstrated that endolithic Chroococidiopsis isolates from deserts around the world synthesize chlorophyll f, an FRL-specialized chlorophyll when FRL is the sole light source. The metagenome-assembled genomes of these isolates encoded chlorophyll f synthase and all the genes required to implement the FaRLiP response. We also present evidence of FRL-induced changes to the major light-harvesting complexes of a Chroococidiopsis isolate. These findings indicate that endolithic cyanobacteria from hyper-arid deserts use FRL photo-acclimation as an adaptation to the unique light transmission spectrum of their rocky habitat.

In hyperarid deserts, endolithic microbial communities colonize the rocks’ interior as a survival strategy. Yet, the composition of these communities and the drivers promoting their assembly are still poorly understood. We analysed the diversity and community composition of endoliths from four different lithic substrates – calcite, gypsum, ignimbrite and granite – collected in the hyperarid zone of the Atacama Desert, Chile. By combining microscopy, mineralogy, spectroscopy and high throughput sequencing, we found these communities to be highly specific to their lithic substrate, although they were all dominated by the same four main phyla, Cyanobacteria, Actinobacteria, Chloroflexi and Proteobacteria. Our finding indicates a fine scale diversification of the microbial reservoir driven by substrate properties. The data suggest that the overall rock chemistry and the light transmission properties of the substrates are not essential drivers of community structure and composition. Instead, we propose that the architecture of the rock, i.e., the space available for colonization and its physical structure, linked to water retention capabilities, is ultimately the driver of community diversity and composition at the dry limit of life., This work was funded by grants NNX15AP18G and NNX15AK57G from NASA, grant DEB1556574 from the NSF to JDR and grant CGL2013‐42509P from the Spanish Ministry of Economy, Industry and Competitiveness to JW, CA, OA, JDR and MCC.

The purpose of the study was to develop a method for locating surface projections of structures related to the radial tunnel using thumb interphalangeal joint (IPJ) coefficients. Distances from vertical and transverse planes through the lateral epicondyle of the humerus to entry (arcade of Frohse – AF) and exit points of the deep branch of the radial nerve (DBRN) from the supinator muscle were measured on nine cadavers. Average distances were used to find coefficients in terms of IPJ widths. The accuracy of using these coefficients in locating the AF was tested by ink injection on five other cadavers. The average IPJ width from these cadaver upper extremities and from an additional sample of 43 healthy adults was approximately 2.0 cm. The mean transverse plane to entry and exit point distances were 4.2 cm (~2 IPJ widths) and 7.6 cm (~3.8 IPJ widths) respectively. The mean vertical plane to entry and exit point distances were 1.9 cm (~1 IPJ width) and 1.0 cm (~0.5 IPJ width) respectively. Mean radial tunne...