Biological Characterization of Microenvironments in a Hypersaline Cold Spring Mars Analog.

Haley M Sapers,Isabelle Raymond-Bouchard,Lyle G Whyte,Gordon R Osinski,Raven Comrey,Jennifer Ronholm

doi:10.3389/fmicb.2017.02527

Haley M Sapers, Isabelle Raymond-Bouchard + Show 4 more

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https://doi.org/10.3389/fmicb.2017.02527

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Abstract

While many habitable niches on Earth are characterized by permanently cold conditions, little is known about the spatial structure of seasonal communities and the importance of substrate-cell associations in terrestrial cyroenvironments. Here we use the 16S rRNA gene as a marker for genetic diversity to compare two visually distinct but spatially integrated surface microbial mats on Axel Heiberg Island, Canadian high arctic, proximal to a perennial saline spring. This is the first study to describe the bacterial diversity in microbial mats on Axel Heiberg Island. The hypersaline springs on Axel Heiberg represent a unique analog to putative subsurface aquifers on Mars. The Martian subsurface represents the longest-lived potentially habitable environment on Mars and a better understanding of the microbial communities on Earth that thrive in analog conditions will help direct future life detection missions. The microbial mats sampled on Axel Heiberg are only visible during the summer months in seasonal flood plains formed by melt water and run-off from the proximal spring. Targeted-amplicon sequencing revealed that not only does the bacterial composition of the two mat communities differ substantially from the sediment community of the proximal cold spring, but that the mat communities are distinct from any other microbial community in proximity to the Arctic springs studied to date. All samples are dominated by Gammaproteobacteria: Thiotichales is dominant within the spring samples while Alteromonadales comprises a significant component of the mat communities. The two mat samples differ in their Thiotichales:Alteromonadales ratio and contribution of Bacteroidetes to overall diversity. The red mats have a greater proportion of Alteromonadales and Bacteroidetes reads. The distinct bacterial composition of the mat bacterial communities suggests that the spring communities are not sourced from the surface, and that seasonal melt events create ephemerally habitable niches with distinct microbial communities in the Canadian high arctic. The finding that these surficial complex microbial communities exist in close proximity to perennial springs demonstrates the existence of a transiently habitable niche in an important Mars analog site.

Highlights

Despite the dominance of permanently cold environments on Earth (Margesin and Miteva, 2011), the biological significance of the cryosphere has only begun to be recognized over the last decade (e.g., Priscu and Christner, 2004)
The system is comprised of 30–40 small outlets concentrated over an area of approximately 3000 m2 in a narrow band (∼300 m long × 30 m wide) that perennially discharge a combined average of 15–20 L s−1 of anoxic [mean oxidoreduction potential (ORP) ∼325 mV] brines (7.5–8% salts) at the base of Expedition Diapiar (Gypsum Hill)
The sequences were relatively evenly distributed between GH4 samples, Gypsum Hill (GH)-4sediment A contained 5849 sequences, GH4-sediment B 4670, green mats 7193, and red mats 8683

Summary

Introduction

Despite the dominance of permanently cold environments on Earth (Margesin and Miteva, 2011), the biological significance of the cryosphere has only begun to be recognized over the last decade (e.g., Priscu and Christner, 2004). Diverse suites of cryophilic microorganisms have successfully colonized these environments and play key ecological roles in carbon and nutrient cycling (Margesin and Miteva, 2011). These extreme environments, characterized by low temperatures and often high salinity are exceptional analogs for putative habitable environments beyond Earth (Fairén et al, 2010; McKay et al, 2012). The physiochemical parameters that characterize the cryoenvironments on Axel Heiberg Island, Canada, and the Gypsum Hill spring system represents a terrestrial analog for putatively habitable subsurface briny aquifers on Mars (Malin and Edgett, 2000; Andersen, 2002; Malin et al, 2006; Rossi et al, 2008; Davila et al, 2010; Fairén et al, 2010; McKay et al, 2012; Battler et al, 2013)

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