| Title | Growth of cyanobacterial soil crusts during diurnal freeze-thaw cycles |
|---|---|
| Author | Steven K. Schmidt* and Lara Vimercati |
| Address | Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, 80309, USA |
| Bibliography | Journal of Microbiology, 57(4),243–251, 2019, |
| DOI | 10.1007/s12275-019-8359-5 |
| Key Words | biological soil crusts, Nostoc commune, terraforming Mars, extremophiles, glacier retreat, soil stabilization, BSCs, astrobiology |
| Abstract | Various Nostoc spp. and related cyanobacteria are able to survive extreme temperatures and are among the most successful colonists of high-elevation sites being exposed due to glacial retreat. It is unclear, however, if cyanobacteria can grow during the extreme freeze-thaw cycles that occur on a yearround basis at high-elevation, peri-glacial sites or if they only grow during the rare periods when freeze-thaw cycles do not occur. We conducted several experiments to determine if cyanobacteria that form biological soil crusts (BSCs) at highelevation sites (> 5,000 m.a.s.l.) in the Andes can grow during diurnal freeze-thaw cycles on a par with those that occur in the field. Here we show that a soil crust that had been frozen at -20°C for five years was able to increase from 40% to 100% soil coverage during a 45-day incubation during which the soil temperature cycled between -12°C and 26°C every day. In a second, experiment an undeveloped soil with no visible BSCs showed a statistically significant shift in the bacterial community from one containing few cyanobacterial sequences (8% of sequences) to one dominated (27%) by Nostoc, Microcoleus, and Leptolyngbya phylotypes during a 77-day incubation with daily freeze-thaw cycles. In addition, counts of spherical Nostoc-like colonies increased significantly on the soil surface during the experiment, especially in microcosms receiving phosphorus. Taken together these results show that freeze-thaw cycles alone do not limit the growth of BSCs in high-elevation soils, and provide new insight into how life is able to thrive in one of the most extreme terrestrial environments on Earth. |