This work considers the hypothetical viability of microbial nitrate-dependent Fe2+ oxidation (NDFO) for supporting simple life in the context of the early Mars environment. This draws on knowledge built up over several decades of remote and in situ observation, as well as recent discoveries that have shaped current understanding of early Mars. Our current understanding is that certain early martian environments fulfill several of the key requirements for microbes with NDFO metabolism. First, abundant Fe2+ has been identified on Mars and provides evidence of an accessible electron donor; evidence of anoxia suggests that abiotic Fe2+ oxidation by molecular oxygen would not have interfered and competed with microbial iron metabolism in these environments. Second, nitrate, which can be used by some iron oxidizing microorganisms as an electron acceptor, has also been confirmed in modern aeolian and ancient sediment deposits on Mars. In addition to redox substrates, reservoirs of both organic and inorganic carbon are available for biosynthesis, and geochemical evidence suggests that lacustrine systems during the hydrologically active Noachian period (4.1–3.7 Ga) match the circumneutral pH requirements of nitrate-dependent iron-oxidizing microorganisms. As well as potentially acting as a primary producer in early martian lakes and fluvial systems, the light-independent nature of NDFO suggests that such microbes could have persisted in sub-surface aquifers long after the desiccation of the surface, provided that adequate carbon and nitrates sources were prevalent. Traces of NDFO microorganisms may be preserved in the rock record by biomineralization and cellular encrustation in zones of high Fe2+ concentrations. These processes could produce morphological biosignatures, preserve distinctive Fe-isotope variation patterns, and enhance preservation of biological organic compounds. Such biosignatures could be detectable by future missions to Mars with appropriate instrumentation.
The draft genomes of the nitrate-dependent iron-oxidizing bacteria Acidovorax sp. strain BoFeN1 and Paracoccus pantotrophus strain KS1 are presented.
Nitrate-dependent Fe2+ oxidation (NDFO) is a microbially mediated process observed in many anaerobic, low-nutrient (oligotrophic) neutral–alkaline environments on Earth, which describes oxidation of Fe2+ to Fe3+ in tandem with microbial nitrate reduction. Evidence suggests that similar environments existed on Mars during the Noachian epoch (4.1–3.7 Ga) and in periodic, localised environments more recently, indicating that NDFO metabolism could have played a role in a potential early martian biosphere. In this paper, three NDFO microorganisms, Acidovorax sp. strain BoFeN1, Pseudogulbenkiania sp. strain 2002 and Paracoccus sp. strain KS1, were assessed for their ability to grow oligotrophically in simulated martian brines and in a minimal medium with olivine as a solid Fe2+ source. These simulant-derived media were developed from modelled fluids based on the geochemistry of Mars sample locations at Rocknest (contemporary Mars soil), Paso Robles (sulphur-rich soil), Haematite Slope (haematite-rich soil) and a Shergottite meteorite (common basalt). The Shergottite medium was able to support growth of all three organisms, while the contemporary Mars medium supported growth of Acidovorax sp. strain BoFeN1 and Pseudogulbenkiania sp. strain 2002; however, growth was not accompanied by significant Fe2+ oxidation. Each of the strains was also able to grow in oligotrophic minimal media with olivine as the sole Fe2+ source. Biomineralised cells of Pseudogulbenkiania sp. strain 2002 were identified on the surface of the olivine, representing a potential biosignature for NDFO microorganisms in martian samples. The results suggest that NDFO microorganisms could have thrived in early martian groundwaters under oligotrophic conditions, depending on the local lithology. This can guide missions in identifying palaeoenvironments of interest for biosignature detection. Indeed, biomineralised cells identified on the olivine surface provide a previously unexplored mechanism for the preservation of morphological biosignatures in the martian geological record.
Astrobiology Graduates in Europe (AbGradE, pronounced ab-grad-ee) is an association of early-career scientists working in fields relevant to astrobiological research. Conceptualized in 2013, it was initially designed as a mini-conference or workshop dedicated to early-career researchers, providing a friendly environment where early-career minds would be able to present their research without being intimidated by the possibility of facing a more traditional audience, composed mainly of senior scientists. Within the last couple of years, AbGradE became the first point of call for European, but also for an increasing number of non-European, early-career astrobiologists. This article aims to present how AbGradE has evolved over the years (in its structure and in its way of organizing events), how it has adapted with the COVID-19 pandemic, and what future developments are considered.
<p><strong>Introduction</strong>: Astrobiology Graduates in Europe (AbGradE, pronounced ab-grad-ee) is an association of early-career scientists working in fields relevant to astrobiological research. Conceptualized in 2013, it was initially designed as a mini-conference dedicated to early-career researchers (ECAs) in a more relaxed environment than that of traditional conferences. Our meetings act as a networking opportunity, as well as a practice round and steppingstone for ECAs entering the world of academic research.</p><p><strong>Audience & topics engaged</strong>: Our audience is mostly composed of graduate students and post-doctoral fellows, but not only: undergraduates, senior scientists, and researchers from different disciplines with a strong interest in astrobiology are also welcome to attend our meetings. The topics engaged at our events, both symposia and workshops, naturally include the obvious themes related to astrobiology, and go beyond them by delving into social sciences and humanities (e.g., an online Space law and governance meeting in 2021). Specific workshops were organized on more practical issues like science communication, space mission design, networking, and navigating post-graduate research. Other issues, like mental health in a research context, are also considered for future editions.</p><p><br><strong>Collaborations</strong>: AbGradE has been involved in astrobiology schools, such as the EANA International hydrothermal spring school. As the spiritual daughter organization of EANA, AbGradE maintains strong ties with it while developing on its own into an organization by ECAs, for ECAs, in a similar fashion to how AbGradCon operates. Over the years, AbGradE also teamed up with other organizations, like the European Astrobiology Campus (EAC), the European Astrobiology Institute (EAI), and the Europlanet Early Career (EPEC) Network.</p><p><br><strong>Online presence</strong>: In the spirit of the &#8220;work from home&#8221; attitude prevalent during the COVID-19 pandemic, AbGradE has attempted to provide more online resources. Apart from moving meetings online, we have built a website and sent out a quarterly newsletter to keep ECAs engaged, and to encourage a sense of community during the lockdown-ridden time of the pandemic.</p><p><br><strong>Scope</strong>: Within the last couple of years, AbGradE became the first point of call for European, but also for an increasing number of non-European ECAs, especially with the recent development of online resources. This presentation aims to present how AbGradE has evolved over the years (in its structure and in its way of organizing events), how it has adapted with the COVID-19 pandemic, and what future developments are considered.</p>
Humanity's interest in whether or not we are alone in the universe spans generations, from Giordano Bruno's 16th century musings on other worlds and Giovanni Schiaparelli reporting seeing ‘canali’ in 1877 on the surface of Mars (which were thought to have been created by intelligent life) to alien invasions portrayed in today's movies. However, it is still unclear if other planetary bodies are capable of supporting life. In the search for life there are two broad areas we look into, the requirements of life and actual signs of life. The identification of the key requirements for life enables scientists to focus life detection efforts onto planets and satellites that are considered habitable and more likely to support life. However, our ability to find life or detect signs of life is based on our understanding of life on Earth.
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