Microbial Community Structure and the Persistence of Cyanobacterial Populations in Salt Crusts of the Hyperarid Atacama Desert from Genome-Resolved Metagenomics.

Kari M Finstad,Alexander J Probst,Alex Echeverría,Gary L Andersen,Jillian F Banfield,Brian C Thomas,Ronald G Amundson,Cecilia Demergasso

doi:10.3389/fmicb.2017.01435

Abstract

Although once thought to be devoid of biology, recent studies have identified salt deposits as oases for life in the hyperarid Atacama Desert. To examine spatial patterns of microbial species and key nutrient sources, we genomically characterized 26 salt crusts from three sites along a fog gradient. The communities are dominated by a large variety of Halobacteriales and Bacteroidetes, plus a few algal and Cyanobacterial species. CRISPR locus analysis suggests the distribution of a single Cyanobacterial population among all sites. This is in stark contrast to the extremely high sample specificity of most other community members. Only present at the highest moisture site is a genomically characterized Thermoplasmatales archaeon (Marine Group II) and six Nanohaloarchaea, one of which is represented by a complete genome. Parcubacteria (OD1) and Saccharibacteria (TM7), not previously reported from hypersaline environments, were found at low abundances. We found no indication of a N2 fixation pathway in the communities, suggesting acquisition of bioavailable nitrogen from atmospherically derived nitrate. Samples cluster by site based on bacterial and archaeal abundance patterns and photosynthetic capacity decreases with increasing distance from the ocean. We conclude that moisture level, controlled by coastal fog intensity, is the strongest driver of community membership.

Highlights

Microbial life has an amazing ability to survive extreme conditions
We identified 14 hidden Markov models (HMM) in the TIGRFAM database4 and ran hmmsearch (HMMER version 3.1b25) on all proteins from the assembled metagenomes using the built-in noise cut-offs for these HMMs
Communities are dominated by Halobacteriales, Bacteroidetes, algae (Chlorophyta), and Cyanobacteria (Figures 2, 3)

Summary

Introduction

Microbial life has an amazing ability to survive extreme conditions. The hyperarid region of the Atacama Desert is one such example. Microbial communities have been observed colonizing translucent salt crust on the surface of evaporitic deposits (Wierzchos et al, 2006). The key to microbial survival there is that halite deliquesces at an atmospheric relative humidity greater than 75%, creating a highly saline solution in its mineral pores (Wierzchos et al, 2012). Due to the frequency of marine fog intrusions in the hyperarid region, these salt crusts deliquesce on a regular basis (Cereceda et al, 2008; Finstad et al, 2016)

Methods

Results

Discussion

Conclusion