The first step in finding potential extant, and/or extinct, life on Mars is to understand the potential biological processes that may have occurred on Mars and identify biosignatures that such processes would generate. This is dependent on identifying and characterising microbial life in suitable terrestrial analogue environments and reliably distinguishing between biotic and abiotic processes. Chemolithotrophic anaerobic microorganisms, such as methanogens, are ideal organisms for investigating potential life in the martian sub-surface as they represent deeply branched terrestrial species that would likely survive there. Furthermore, the carbon dioxide and hydrogen required for their metabolism are provided by the approximately 96% carbon dioxide atmosphere and hydrogen produced in serpentinisation and other reactions

Curtis-Harper, E.

Olsson-Francis, K.

Pearson, V. K.

Schwenzer, S. P.

English

Open Research Online

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsThe anaerobic community of an estuarine environment:an analogue for life on MarsConference or Workshop ItemHow to cite:Curtis-Harper, E.; Pearson, V. K.; Schwenzer, S. P. and Olsson-Francis, K. (2014). The anaerobic communityof an estuarine environment: an analogue for life on Mars. In: 12th Early Career Planetary Scientists’ Meeting, 19-20Feb 2015, University of Kent, UK Planetary Forum.For guidance on citations see FAQs.c© 2015 The AuthorsVersion: Version of RecordCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukThe anaerobic community of an estuarine environment: an analogue for life on Mars.  E.Curtis-Harper, V.K.Pearson, S.P.Schwenzer and K.Olsson-Francis. The Open University. Walton Hall, Milton Keynes, MK7 6AA, UK; E-mail: Elliot.curtis-harper@open.ac.uk Introduction:  The first step in finding potential extant, and/or extinct, life on Mars is to understand the potential biological processes that may have occurred on Mars and identify biosignatures that such processes would generate. This is dependent on identifying and characterising microbial life in suitable terrestrial analogue environments and reliably distinguishing between biotic and abiotic processes. Chemolithotrophic anaerobic microorganisms, such as methanogens, are ideal organisms for investigating potential life in the martian sub-surface[1] as they represent deeply branched terrestrial species that would likely survive there. Furthermore, the carbon dioxide and hydrogen required for their metabolism are provided by the approximately 96% carbon dioxide atmosphere[2] and hydrogen produced in serpentinisation and other reactions[3].  In this study, we used a community of anaerobic microorganisms (Fig.1), which were isolated from below the redox potential discontinuity (RPD) layer of the River Dee estuary, UK. The anaerobic conditions, the 11-15˚C temperature and high salinity (37g/l NaCl) make the sub-RPD zone an ideal analogue for the martian subsurface.   Methods: Using MiSeq sequencing we investigated the composition of the microbial community, which included sulfate reducing bacteria (Fig. 1). Anaerobic growth experiments were conducted using a minimal growth medium containing dd H2O, sodium lactate (carbon source), ammonium chloride (nitrogen source) and thioglycollate and ascorbic acid reducing agents. The remaining bioessential elements were provided by a Mars analogue rock mix consisting of a non-amygdaloidal terrestrial basalt from Le Cheix Quarry and aegirine in the ratio 1.75:1 respectively. These geological substrates were geochemically characterized by XRF and XRD and shown to be a compositional analogue for the Rocknest site on Mars[4].  Growth was measured using cell counts.  The dissolution kinetics will be determined by analysing the release of key elements, such as Si, Ca, K, Fe in the growth medium with ICP-AES (results pending). Gas Chromatography was carried out on aliquots of the headspace gas to investigate the presence of methane, which is a byproduct of methanogen metabolism.       Results/Discussion: The growth curve displayed in Fig. 2 demonstrates that the microbial community was able to grow in the nutrient poor minimal growth medium, utilising the bio-essential elements provided by the Mars analog substrates. Abiotic controls were treated identically and no growth was observed. Thus a varied anaerobic microbial community, which contains chemolithotrophs, can utilize a Mars analogue rock substrate.   The growth curve suggests a possible biphasic growth. The simultaneous fluctuations in methane concentrations may suggest a relationship between methanogenic and methanotrophic microoorganisms whereby the secondary exponential growth phase can be attributed to methanotrophs utilizing methane produced when the methanogenic archaea exponentially grow. MiSeq sequencing has already been used to identify the presence of methanotrophic bacteria in our samples and further analysis of the archaeal community, using MiSeq analysis, will confirm whether methanogenic archaea are present.  Further experimental work will focus on identifying geochemical biomarkers formed as a result of the presence of the microbial community by comparing ICP-AES data for media aliquots taken from biotic and abiotic samples. Conclusions: This study demonstrates that the microbial community below the RPD of the River Dee Estuary can act as an informative analogue in studies of Martian habitability and life detection. Thus it should be possible to identify biosignatures in the Mars analogue substrate to inform future Mars life detection missions. References: [1] Weiss B. P., Yung Y. L. and Nealson K. H. 2000. PNAS. 97(4):1395–1399. [2] Mahaffy P. et al 2013 Science, 341(1997): 263-266 [3] Hellevang H., Huang S. and Thorseth I. 2011 Astrobiology 11(7): 711-724. [4] Schmidt M., Campbell J. and Gellert R. 2014 Journal of Geophysical Research: Planets 119(1): 64-81 MethaCellFigure 1. MiSeq analysis on DNA extracted from the River Dee sub-RPD sample. Figure 2. Cell growth as measured by direct cell enumeration plotted with CH4 concentrations in the gas headspace over time  

The anaerobic community of an estuarine environment: an analogue for life on Mars

In this study, we used microbiological techniques in combination with several analytical geochemical techniques to identify potential biomarkers for life on Mars. A community of anaerobic microorganisms containing chemolithoautotrophs was isolated from below the redox potential discontinuity (RPD) layer. The anaerobic conditions, the 11-15 ˚C temperature and high salinity (37 g l-1 NaCl) make the sub-RPD zone an ideal environment to sample a biological analogue for the martian subsurface. Samples were collected from the River Dee estuary, UK, for use in this study.



Anaerobic growth experiments were conducted using a water-based minimal growth medium containing sodium lactate (carbon source), ammonium chloride (nitrogen source), and thioglycollate and ascorbic acid (reducing sources). Bioessential elements were provided by a Mars analogue substrate consisting of a mix of non-amygdaloidal terrestrial basalt and aegirine, an iron rich silicate. The experiments were carried out under a representative Mars gas headspace and buffered using sodium bicarbonate.



Direct cell counts demonstrated that the microbial community could grow by utilising the Mars analogue as their only source of bioessential minerals. The dissolution kinetics were determined from the concentration of key elements (such as Si, Ca, K, Fe) in the growth medium measured by ICP-AES. Gas chromatography was carried out on aliquots of the headspace gas to measure the concentration of methane, which is a byproduct of methanogen metabolism. Preliminary comparisons of headspace methane in biotic and abiotic replicates suggest abiotic production of methane to be significant in this system.



The results from this study demonstrate that a mixed community of anaerobic microorganisms can be supported nutritionally by the release of bioessential minerals from a Mars analogue substrate under a compositionally accurate martian atmosphere. Future work will analyse the elements released during biotic and abiotic dissolution and investigate the precipitation of secondary minerals during these experiments, since these may be indicative of processes that could elucidate biomarkers for life detection on Mars

Curtis-Harper, Elliot

Olsson-Francis, Karen

Schwenzer, Susanne

Pearson, Victoria

The anaerobic community of an estuarine environment: an analogue for life on Mars.

The first step in finding potential extant, and/or extinct, life on Mars is to understand the potential biological processes that may have occurred on Mars. This is dependent on identifying and characterising microbial life in suitable terrestrial analogue environments. Chemolithotrophic anaerobic microorganisms, such as methanogens, are ideal organisms for investigating potential life on Mars.



In this study, we used a community of chemolithotrophic anaerobic microorganisms, which were isolated from below the redox potential discontinuity (RPD) layer of the River Dee estuary, UK. The anaerobic conditions, the 11-15˚C temperature and high salinity make the sub-RPD zone an ideal analogue for the Martian subsurface. Using 454 sequencing we investigated the composition of the microbial community which included sulfate reducing bacteria. Anaerobic growth experiments were conducted with a basalt and aegirine growth medium, which were used as an analogue for the composition of the Rocknest site on Mars.



The microbial community was able to grow, utilising the bio-essential elements in the growth medium. The dissolution kinetics were determined by measuring the release of key elements, such as Si, Ca, K, Fe in the growth medium with ICP-AES and growth was measured by cell counts The results from this study demonstrate that the microbial community below the RPD can act as an informative analogue in studies of Martian habitability and life detection

Pearson, V.

Schwenzer, S.

http://oro.open.ac.uk/44391/7/UKPF%202015%20v7%20final.pdf

The anaerobic community of an estuarine environment: an analogue for life on Mars

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