Ivan G. Paulino-Lima

Isolation of UVC-tolerant bacteria from the Hyperarid Atacama Desert, Chile

Martian surface microbial inhabitants would be challenged by a constant and unimpeded flux of UV radiation, and the study of analog model terrestrial environments may be of help to understand how such life forms could survive under this stressful condition. One of these environments is the Atacama Desert (Chile), a well-known Mars analog due to its extreme dryness and intense solar UV radiation. Here, we report the microbial diversity at five locations across this desert and the isolation of UVC-tolerant microbial strains found in these sites. Denaturing gradient gel electrophoresis (DGGE) of 16S rDNA sequences obtained from these sites showed banding patterns that suggest distinct and complex microbial communities. Analysis of 16S rDNA sequences obtained from UV-tolerant strains isolated from these sites revealed species related to the Bacillus and Pseudomonas genera. Vegetative cells of one of these isolates, Bacillus S3.300-2, showed the highest UV tolerance profile (LD10u2009=u2009318xa0Ju2009m2), tenfold higher than a wild-type strain of Escherichia coli. Thus, our results show that the Atacama Desert harbors a noteworthy microbial community that may be considered for future astrobiological-related research in terms of UV tolerance.

Surface biosignatures of exo-Earths: Remote detection of extraterrestrial life

Significance We develop the first catalogue, to our knowledge, of reflectance spectra for a diverse range of pigmented microorganisms, including ones that were isolated from Earth’s most extreme environments. This catalogue provides a broad scope of surface signatures for life on exoplanets, which could provide different conditions from those on Earth, allowing, for example, extremophiles on Earth to become the predominant life form. Much of the history of life on Earth has been dominated by microbial life, and it is likely that life on exoplanets evolves through single-celled stages prior to multicellular creatures. Here, we present the first database, to our knowledge, for such surface features in preparation for the next generation of space- and ground-based telescopes that will search for a wide variety of life on exoplanets. Exoplanet discovery has made remarkable progress, with the first rocky planets having been detected in the central star’s liquid water habitable zone. The remote sensing techniques used to characterize such planets for potential habitability and life rely solely on our understanding of life on Earth. The vegetation red edge from terrestrial land plants is often used as a direct signature of life, but it occupies only a small niche in the environmental parameter space that binds life on present-day Earth and has been widespread for only about 460 My. To more fully exploit the diversity of the one example of life known, we measured the spectral characteristics of 137 microorganisms containing a range of pigments, including ones isolated from Earth’s most extreme environments. Our database covers the visible and near-infrared to the short-wavelength infrared (0.35–2.5 µm) portions of the electromagnetic spectrum and is made freely available from biosignatures.astro.cornell.edu. Our results show how the reflectance properties are dominated by the absorption of light by pigments in the visible portion and by strong absorptions by the cellular water of hydration in the infrared (up to 2.5 µm) portion of the spectrum. Our spectral library provides a broader and more realistic guide based on Earth life for the search for surface features of extraterrestrial life. The library, when used as inputs for modeling disk-integrated spectra of exoplanets, in preparation for the next generation of space- and ground-based instruments, will increase the chances of detecting life.

Schrödinger’s microbes: Tools for distinguishing the living from the dead in microbial ecosystems

While often obvious for macroscopic organisms, determining whether a microbe is dead or alive is fraught with complications. Fields such as microbial ecology, environmental health, and medical microbiology each determine how best to assess which members of the microbial community are alive, according to their respective scientific and/or regulatory needs. Many of these fields have gone from studying communities on a bulk level to the fine-scale resolution of microbial populations within consortia. For example, advances in nucleic acid sequencing technologies and downstream bioinformatic analyses have allowed for high-resolution insight into microbial community composition and metabolic potential, yet we know very little about whether such community DNA sequences represent viable microorganisms. In this review, we describe a number of techniques, from microscopy- to molecular-based, that have been used to test for viability (live/dead determination) and/or activity in various contexts, including newer techniques that are compatible with or complementary to downstream nucleic acid sequencing. We describe the compatibility of these viability assessments with high-throughput quantification techniques, including flow cytometry and quantitative PCR (qPCR). Although bacterial viability-linked community characterizations are now feasible in many environments and thus are the focus of this critical review, further methods development is needed for complex environmental samples and to more fully capture the diversity of microbes (e.g., eukaryotic microbes and viruses) and metabolic states (e.g., spores) of microbes in natural environments.

UV‐resistant yeasts isolated from a high‐altitude volcanic area on the Atacama Desert as eukaryotic models for astrobiology

The Sairecabur volcano (5971 m), in the Atacama Desert, is a high‐altitude extreme environment with high daily temperature variations, acidic soils, intense UV radiation, and low availability of water. Four different species of yeasts were isolated from this region using oligotrophic media, identified and characterized for their tolerance to extreme conditions. rRNA sequencing revealed high identity (>98%) to Cryptococcus friedmannii, Exophiala sp., Holtermanniella watticus, and Rhodosporidium toruloides. To our knowledge, this is the first report of these yeasts in the Atacama Desert. All isolates showed high resistance to UV‐C, UV‐B and environmental‐UV radiation, capacity to grow at moderate saline media (0.75–2.25 mol/L NaCl) and at moderate to cold temperatures, being C. friedmannii and H. watticus able to grow in temperatures down to −6.5°C. The presence of pigments, analyzed by Raman spectroscopy, correlated with UV resistance in some cases, but there is evidence that, on the natural environment, other molecular mechanisms may be as important as pigmentation, which has implications for the search of spectroscopic biosignatures on planetary surfaces. Due to the extreme tolerances of the isolated yeasts, these organisms represent interesting eukaryotic models for astrobiological purposes.

Extremely high UV-C radiation resistant microorganisms from desert environments with different manganese concentrations

Desiccation resistance and a high intracellular Mn/Fe ratio contribute to ionizing radiation resistance of Deinococcus radiodurans. We hypothesized that this was a general phenomenon and thus developed a strategy to search for highly radiation-resistant organisms based on their natural environment. While desiccation is a typical feature of deserts, the correlation between radiation resistance and the intracellular Mn/Fe ratio of indigenous microorganisms or the Mn/Fe ratio of the environment, has not yet been described. UV-C radiation is highly damaging to biomolecules including DNA. It was used in this study as a selective tool because of its relevance to early life on earth, high altitude aerobiology and the search for life beyond Earth. Surface soil samples were collected from the Sonoran Desert, Arizona (USA), from the Atacama Desert in Chile and from a manganese mine in northern Argentina. Microbial isolates were selected after exposure to UV-C irradiation and growth. The isolates comprised 28 genera grouped within six phyla, which we ranked according to their resistance to UV-C irradiation. Survival curves were performed for the most resistant isolates and correlated with their intracellular Mn/Fe ratio, which was determined by ICP-MS. Five percent of the isolates were highly resistant, including one more resistant than D. radiodurans, a bacterium generally considered the most radiation-resistant organism, thus used as a model for radiation resistance studies. No correlation was observed between the occurrence of resistant microorganisms and the Mn/Fe ratio in the soil samples. However, all resistant isolates showed an intracellular Mn/Fe ratio much higher than the sensitive isolates. Our findings could represent a new front in efforts to harness mechanisms of UV-C radiation resistance from extreme environments.

Synthetic Biology for Space Exploration: Promises and Societal Implications

Synthetic biology can greatly accelerate the development of human space exploration, to the point of allowing permanent human bases on Mars within our lifetime. Among the technological issues to be tackled is the need to provide the consumables required to sustain crews, and using biological systems for the on-site production of resources is an attractive approach. However, all organisms we currently know have evolved on Earth and most extraterrestrial environments stress the capabilities of even terrestrial extremophiles. Two challenges consequently arise: organisms should survive in a metabolically active state with minimal maintenance requirements, and produce compounds of interest while relying only on inputs found in the explored areas. A solution could come from the tools and methods recently developed within the field of synthetic biology. The societal implications are complex: there are implications with synthetic biology and human space colonization independently, and together there are potentially more issues. Establishing colonies relying to a large extent on modified organisms and transferring the developed technologies to terrestrial applications raises a wide range of critical ethical questions and unprecedented societal impacts, on Earth as well as on colonized planetary bodies. The scenario of humans as a multi-planet species should be addressed now, as technologies aimed at making it happen are already under development. Here we give a brief overview of the synthetic biology technologies that are being developed to aid human space exploration, before discussing the impacts of proposed medium-term scenarios on the evolution of our society.

Mini-Review: Probing the limits of extremophilic life in extraterrestrial environment-simulated experiments

The results obtained in these experiments have revealed a remarkable resistance of extremophilic bacteria and archaea against different radiation sources (VUV, solar wind simulants, X rays) whenever protected by microsized carbonaceus grains. Altogether, the collected data suggest the interesting possibility of the existence of microbial life beyond Earth and its transfer among habitable bodies, which we have called microlithopanspermia.

Draft Genome Sequence of Hymenobacter sp. Strain AT01-02, Isolated from a Surface Soil Sample in the Atacama Desert, Chile.

ABSTRACT Here, we report the 5.09-Mb draft genome sequence of Hymenobacter sp. strain AT01-02, which was isolated from a surface soil sample in the Atacama Desert, Chile. The isolate is extremely resistant to UV-C radiation and is able to accumulate high intracellular levels of Mn/Fe.