A Submersible, Off-Axis Holographic Microscope for Detection of Microbial Motility and Morphology in Aqueous and Icy Environments

• Main Authors: Lovejoy, Connie, Lindensmith, Christian A., Rider, Stephanie, Bedrossian, Manuel, Wallace, J. Kent, Serabyn, Eugene, Showalter, G. Max, Deming, Jody W., Nadeau, Jay L.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Public Library of Science 2016
• Subjects: Greenland; Nuuk; Sea ice
• Online Access: https://doi.org/10.1371/journal.pone.0147700; https://www.ncbi.nlm.nih.gov/pmc/PMC4422661

Sea ice is an analog environment for several of astrobiology's near-term targets: Mars, Europa, Enceladus, and perhaps other Jovian or Saturnian moons. Microorganisms, both eukaryotic and prokaryotic, remain active within brine channels inside the ice, making it unnecessary to penetrate through to liquid water below in order to detect life. We have developed a submersible digital holographic microscope (DHM) that is capable of resolving individual bacterial cells, and demonstrated its utility for immediately imaging samples taken directly from sea ice at several locations near Nuuk, Greenland. In all samples, the appearance and motility of eukaryotes were conclusive signs of life. The appearance of prokaryotic cells alone was not sufficient to confirm life, but when prokaryotic motility occurred, it was rapid and conclusive. Warming the samples to above-freezing temperatures or supplementing with serine increased the number of motile cells and the speed of motility; supplementing with serine also stimulated chemotaxis. These results show that DHM is a useful technique for detection of active organisms in extreme environments, and that motility may be used as a biosignature in the liquid brines that persist in ice. These findings have important implications for the design of missions to icy environments and suggest ways in which DHM imaging may be integrated with chemical life-detection suites in order to create more conclusive life detection packages. © 2016 Lindensmith et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Received: November 17, 2015. Accepted: January 7, 2016. Published: January 26, 2016. This work was supported by the Gordon and Betty Moore Foundation (GBMF) grant numbers 4037 (McGill University, JN, subcontract to University of Washington, JWD, GMS) and 4038 (California Institute of Technology, CAL, SR, ...