Heterotrophic Microbial Colonization of the Interior of Shocked Rocks from the Haughton Impact Structure, Devon Island, Nunavut, Canadian High Arctic
The polar desert is one of the most extreme environments on Earth. In these regions, microorganisms have had to develop novel strategies and adaptations in order to survive. One of the most effective such strategies has been developed by mkroorganisms, known as endoliths, which live in the interior of rocks, escaping or mitigating the hazards of the polar desert and fully utilizing the resources available in the rock environment. The most studied groups of polar endoliths are near-surface phototrophic communities inhabiting porous sedimentary rocks in Antarctica. Here we examine a novel environment for endolithic communities: crystalline rocks that have undergone shock metamorphosis as a result of a comet or asteroid impact. Specifically, we present a characterization of the heterotrophic endolithic community and its environment in the interior of impact-shocked gneiss and breccia samples from Haughton Impact structure on Devon Island, Nunavut, in the Canadian High Arctic. The high-latitude and arid, polar climate at Haughton preclude significant populations of higher-order organisms, naturally restricting the impact structure ecosystem to microbial communities. As such, it provides a unique opportunity to examine, in a natural setting, the microbiological colonization of impact-shocked rocks. This colonization is facilitated primarily by the creation of interconnected fissures and vesicles throughout the sample, which serve as microbial habitats. Twenty-seven heterotrophic bacteria have been isolated from the samples of shocked rocks: fourteen from shocked gneiss and thirteen from breccia. Genes encoding the 16S rRNA of the isolates were sequenced to identify the isolates and characterize the community inhabiting the shocked rocks. The bacteria inhabiting the shocked gneiss and the breccia show great similarity to each other, and also to other heterotrophic communities isolated from polar environments. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis were used together to document the in situ growth of these microbes, either in small groups or in large biofilms, in the interior of the samples, where they take advantage of impact-induced inhomogeneities in surface composition and inhabit cavities created by the impact-induced shock. The interiors of shocked crystalline rocks are observed to provide abundant habitats for heterotrophic bacteria, particularly as compared to unshocked samples, demonstrating, through habitat generation, the beneficial role that impact events can play in microbial ecosystems. The discovery of these heterotrophic communities within impact-shocked crystalline rocks extends our knowledge of the habitable biosphere on Earth. The colonization of the interiors of these samples has significant astrobiological applications both for considering terrestrial, microbiological contamination of meteorites from the Antarctic ice sheet and for investigating possible habitats for microbial organisms on the early Earth, and more speculatively, on Mars.