Metabolomics as an Emerging Tool in the Search for Astrobiologically Relevant Biomarkers

It is now routinely possible to sequence and recover microbial genomes from environmental samples. To the degree it is feasible to assign transcriptional and translational functions to these genomes, it should be possible, in principle, to largely understand the complete molecular inputs and outputs of a microbial community. However, gene-based tools alone are presently insufficient to describe the full suite of chemical reactions and small molecules that compose a living cell. Metabolomic tools have developed quickly and now enable rapid detection and identification of small molecules within biological and environmental samples. The convergence of these technologies will soon facilitate the detection of novel enzymatic activities, novel organisms, and potentially extraterrestrial life-forms on solar system bodies. This review explores the methodological problems and scientific opportunities facing researchers who hope to apply metabolomic methods in astrobiology-related fields, and how present challenges might be overcome.With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737

Cosmopolitan heterotrophic microeukaryotes are active bacterial grazers in experimental oil-polluted systems

We investigated the population dynamics and prevailing 18S rDNA phylotypes of microeukaryotes (<= 10 mu m) in microcosms containing seawater from either an unpolluted oligotrophic site or a chronically oil-polluted mesotrophic site of the Aegean Sea, amended with crude oil (100 p.p.m. final concentration) and crude oil plus emulsifier (10 p.p.m. final concentration). The addition of oil alone did not result in an important increase of bacteria or their predators, while the addition of oil and emulsifiers caused an important increase in bacteria followed by nanoflagellate predator response. We observed an important shift in the microeukaryotic community structure, which was characterized by the dominance of the same heterotrophic nanoflagellates in all oil-polluted treatments. Thus, the resulting 18S rDNA phylotypes were dominated (48.1-82.4%) by Paraphysomonas foraminifera in all treatments containing crude oil and crude oil plus emulsifier. The origin of the seawater, i.e. unpolluted versus chronically oil-polluted, had no effect on the dominant eukaryote, suggesting that the ubiquitous P. foraminifera is an effective opportunist in oil-polluted aquatic systems. The next dominant phylotypes were Monosiga brevicollis (<= 27.0%) and Pseudobodo tremulans (<= 23.1%). However, the addition of the emulsifier increased the dominance of P. foraminifera but decreased that of M. brevicollis and P. tremulans. Our study revealed that these dominant oil-tolerant eukaryotes, which are commonly found in the marine environments, are important grazers of bacteria and as such their dynamics should be taken into account in bioremediation practices in situ