Microbial Population and Distribution at a Mars Analog Alluvial Plain in Dyngjusandur, Iceland

The limited nutrient availability, extreme temperatures, and desiccation of Arctic volcanic regions provide a unique opportunity to study environments with multiple similarities to extraterrestrial systems. Dyngjusandur, Iceland, is a plain of nutrient-poor volcanic basaltic tephra shaped by alluvial and aeolian action, sharing spectroscopic similarities to analogous geological features observed on Mars. To obtain spatial information at different scales, two regions of the Dyngjusandur plain separated by 1 km and selected for their homogeneous appearance were sampled in this study. Sampling schemes each consisted of nested triangular grids of samples beginning at the 0.1 m scale and increasing to the 100 m scale. Additional samples were recovered in 1 cm increments to a depth of 7 cm. Biological and geophysical analyses were performed including 16S rRNA gene qPCR, DNA quantification, amplicon sequencing, moisture quantification, and separation of grain size fractions. The two sampling sites were found to have significantly different dsDNA content by the t-test (p-value = 0.001) and the Mann–Whitney u-test (p-value = 0.003). The DNA content (a proxy for biomass) showed the greatest variation at 10 m of sample separation, and both total dsDNA content and bacterial 16S rRNA gene copies showed significant correlations with sample grain size. Grain size distribution also appeared to influence the abundance of several bacterial phyla, with positive and negative correlations observed, though the same dominant phyla were observed across all samples studied. This work suggests that, in seemingly homogeneous environments undergoing aeolian resurfacing, the averages from a sample set collected at small spatial separation (1–10 m) may be sufficient to define baseline levels of biomass present and the abundances of the most prominent phyla on a larger (100 m–1 km) scale. However, sampling a larger site at smaller intervals (10 m) provides important characterization of site heterogeneity with diminishing information returns at increasingly smaller intervals (≤1 m).