Characterization of microbial communities and nutrient dynamics in Mars-analogous soils of the Atacama Desert

Abstract

The Atacama Desert located in northern Chile is a harsh terrestrial environment analogous to Mars in multiple physicochemical aspects, such as its hyperaridity, a similar landscape, lack of water weathering, high UV radiation, an organic carbon-depleted condition, and an extensive reservoir of oxidants. Nitrate and phosphate minerals as potential bioessential N/P sources are abundant in both Atacama and Mars oligotrophic soils. Hence, biosignatures that affect the stable isotope fractionations of these salts are potential targets for life detection on Mars. This study applied 16S rRNA sequencing and pathway inferences to identify the Atacama microbial community compositions and functions along a latitudinal gradient from the northern hyperarid core to the southern transition zone. Due to a 19.6 mm rainfall event six months before sampling, microbial communities of the hyperarid site shifted to a structure pattern more similar to the Actinobacteria-dominated transition zone. The microbiome in an evaporitic salt flat, Salar de Llamara in the Atacama Desert, was also examined to understand another type of Mars analog. In the powdery crust of Llamara, Proteobacteria, Bacteroidetes, and Cyanobacteria were dominant. Illumina might be a better platform than Roche 454 to sequence these Cyanobacteria-rich soils for deeper sequencing coverage. Additionally, stable isotope geochemical analyses were performed to assess the isotopic biosignatures imprinted in nitrate and phosphate. Dependent on pathway inference and isotope results, microbial nitrate consumption and nitrification became more active as the aridity decreased. Phosphate oxygen isotopes suggested that when the annual precipitation was more than 15 mm, biogenic signals overprinted the pedogenic signature. Meanwhile, to develop a simple and cheap method for separating nitrate and sulfate, a resin column-based extraction method was designed and evaluated. This project contributed to the understanding of microbiomes and their impacts on nutrient dynamics in Mars-analogous environments, and supported future Mars life detection missions.

Date of Award	1 Dec 2021
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Mark Claire (Supervisor) & Aubrey Lea Zerkle (Supervisor)