Effect of soil horizon stratigraphy on the microbial ecology of alpine paleosols.

There is remarkable potential for research at the interface between the earth sciences and environmental microbiology that may lead to advances in our understanding of the role of bacterial communities in the surface or subsurface environment of our planet. One mainstay of sedimentary classification is the concept of differential soil and/or paleosol horizons being the result of primarily physical and chemical weathering, with relatively little understanding of how microbial communities between these stratified horizons differ, if at all. In this study we evaluate the differences in microbial community taxonomy and biogeochemical functional potential between stratified soil horizons in an alpine paleosol environment using next-generation sequencing (NGS) shotgun sequencing. Paleosols represent a unique environment to study the effect of differences soil horizon environments on the microbial community due to their relative isolation, and the fact that three distinct stratified soil horizons can be identified within the top 30 cm of the soil. This enables us to assess variation in microbial community composition that will be relatively distinct from variation due to distance alone. We test the hypothesis that variation in soil community composition is linked to variation in the physical and chemical parameters that define stratigraphy. Multivariate statistical analysis of sequencing reads from soil horizons across five sampling sites revealed that 1223 microbial genera vary significantly and consistently in abundance across stratified soil horizons at class level. Specifically Ktedonobacter, Bacilli and Betaproteobacteria responded most strongly to soil depth. Alpha diversity showed a positive correlation with soil depth. Beta diversity, however, did not differ significantly between horizons. Genes involved in carbohydrate and nitrogen metabolism were found to be more abundant in Ah horizon samples. Closer inspection of carbohydrate metabolism genes revealed that genes involved in CO2 fixation, fermentation and saccharide metabolism decreased in abundance with depth while one­carbon metabolism increased down profile.

Bornean orangutan geophagy: analysis of ingested and control soils.

Geophagy among orangutans is the most poorly documented in contrast to the knowledge of soil-eating practices of other great ape species. Observations of soil consumption by orangutans in the Sungai Wain Forest Preserve (Wanariset) of Borneo are presented, along with physico-mineral-chemical analyses of the ingested soil in an effort to understand what might stimulate the activity. The consumed soils are: light colored, not excessively weathered by normal standards, higher in the clay size fraction relative to controls, and are comprised of a mix of clay minerals without any specificity of 1:1, 2:1 and/or 2:1:1 (Si:Al) species. The geophagic soils contain chlorides below detection limits, effectively eliminating salt as a stimulus. Soil chemical and geochemical analyses confirm that orangutans prefer soils with pH levels near or above 4.0, while controls are consistently lower (pH = 3.5-4.0), a considerable difference in acidity for at least four out of six soils consumed. Geochemical analysis shows Al, Fe and K are high in the consumed vs control samples; higher Al follows from higher clay percentages in the consumed earth. Iron and K may play physiological roles, but Fe is mostly in the ferrous form (Fe(+2)) and may not be readily taken up by the animals. The preferential choice of consumed samples, with pH above 4.0 and higher clay contents, may promote a more beneficial intestinal environment.

Bayesian chronological analyses consistent with synchronous age of 12,835-12,735 Cal B.P. for Younger Dryas boundary on four continents.

The Younger Dryas impact hypothesis posits that a cosmic impact across much of the Northern Hemisphere deposited the Younger Dryas boundary (YDB) layer, containing peak abundances in a variable assemblage of proxies, including magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, nanodiamonds, carbon spherules, aciniform carbon, platinum, and osmium. Bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,835-12,735 Cal B.P. at 95% probability. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas. Two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the YDB layer within the limits of dating uncertainty (∼ 100 y). The widespread distribution of the YDB layer suggests that it may serve as a datum layer.

Planetary imaging in powers of ten: a multiscale, multipurpose astrobiological imager.

Contextual, multiscale astrobiological imaging is necessary to discover, map, and image patchy microbial colonization in extreme environments on planetary surfaces. The large difference in scale--several orders of magnitude--between search environment and microorganisms or microbial communities represents a challenge, which to date no single imaging instrument is able to overcome. In support of future planetary reconnaissance missions, we introduce an adapter-based imager, built from an off-the-shelf consumer digital camera, that offers scalable imaging ranging from macroscopic (meters per pixel) to microscopic (micrometers per pixel) imaging, that is, spanning at least 6 orders of magnitude. Magnification in digital cameras is governed by (1) the native resolution of the CCD/CMOS chip of the camera, (2) the distance between camera and object to be imaged (focal length), and (3) the built-in optical and digital zoom. Both telezoom and macro mode alone are usually insufficient for microscopic imaging. Therefore, the focal distance has to be shortened, and the native CCD resolution of the camera has to be increased to attain a microscopic imaging capability. Our adapter-based imager bridges the gap between macroscopic and microscopic imaging, thereby enabling for the first time contextual astrobiological imaging with the same instrument. Real-world applications for astrobiology and planetary geology are discussed, and proof-of-concept imagery taken with our prototype is presented.

A bacterial enrichment study and overview of the extractable lipids from paleosols in the Dry Valleys, Antarctica: implications for future Mars reconnaissance.

The Dry Valleys of Antarctica are one of the coldest and driest environments on Earth with paleosols in selected areas that date to the emplacement of tills by warm-based ice during the Early Miocene. Cited as an analogue to the martian surface, the ability of the Antarctic environment to support microbial life-forms is a matter of special interest, particularly with the upcoming NASA/ESA 2018 ExoMars mission. Lipid biomarkers were extracted and analyzed by gas chromatography--mass spectrometry to assess sources of organic carbon and evaluate the contribution of microbial species to the organic matter of the paleosols. Paleosol samples from the ice-free Dry Valleys were also subsampled and cultivated in a growth medium from which DNA was extracted with the explicit purpose of the positive identification of bacteria. Several species of bacteria were grown in solution and the genus identified. A similar match of the data to sequenced DNA showed that Alphaproteobacteria, Gammaproteobacteria, Bacteriodetes, and Actinobacteridae species were cultivated. The results confirm the presence of bacteria within some paleosols, but no assumptions have been made with regard to in situ activity at present. These results underscore the need not only to further investigate Dry Valley cryosols but also to develop reconnaissance strategies to determine whether such likely Earth-like environments on the Red Planet also contain life.

Understanding geophagy in animals: standard procedures for sampling soils.

Geophagy or soil ingestion is a multidisciplinary phenomenon that has attracted the attention of many researchers in recent years; who have sought to understand why a large number of animals consume natural earths. To find out why animals ingest soils, it is of paramount importance to establish standard methods to analyze comestible soil. Researchers have used different methods to examine soils ingested by animals, often with incomplete or inconclusive results. To make meaningful comparisons among studies, it is necessary to perfect research designs and establish standard methods to evaluate and analyze geophagy in animals.