The composition of endolithic communities in gypcrete is determined by the specific microhabitat architecture
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 rock-bottom layer) microhabitats. A combination of microscopy investigations strategies and high-throughput sequencing approaches were used to characterize the endolithic communities at the microscale in these microhabitats within the same piece of lithic substrate. Microscopy techniques revealed differences in the architecture of the endolithic microhabitats and in 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. These results show, for the first time, that the differences in the architecture of a microhabitat, even within the same piece of lithic substrate, might be an essential factor in shaping the diversity and composition of endolithic microbial communities.