Cryptoendolith alteration of Antarctic sandstone substrates: pioneers or opportunists?

Introduction: Lichen dominated cryptoendolithic communities from the Dry Valleys of Antarctica have been the subject of much research over recent years owing to their potential as analogues of Martian lifeforms. This is primarily owing to the stress tolerant nature of the microorganisms, remarkable adaptive achievements and the similarities between the Antarctic Dry Valley ecosystems and conditions pertaining at the Martian surface. Endolithic microbial communities have a photosynthetic primary producer, so translucent rocks through which sunlight can penetrate are their only suitable substrate. They also favour colonization of rocks which either have a porous structure or are weathered and permeated by fractures, as they are reported not to penetrate the substrate by solution [1]. The predominant rock-colonizing organisms are cryptoendolithic lichens [1]. They form conspicuous multicoloured zones under the surface of the Beacon Sandstones. All zones are produced by filamentous fungi (mycobionts) and unicellular green algae (phycobionts), which together form a symbiotic lichen association.