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.