Characteristic Raman Bands of Amino Acids and Halophiles as Biomarkers in Planetary Exploration

404 Pages·2017·9.98 MB·English

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Characteristic Raman Bands of Amino Acids and
Halophiles as Biomarkers in Planetary Exploration
Thesis
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Rolfe, Samantha (2017). Characteristic Raman Bands of Amino Acids and Halophiles as Biomarkers in Planetary
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Characteristic Raman Bands of Amino Acids and Halophiles as
Biomarkers in Planetary Exploration

Samantha Melanie Rolfe
MPhys (Hons), University of Leicester, 2010

September 2016

The Open University
School of Physical Sciences

A THESIS SUBMITTED TO THE OPEN UNIVERSITY IN THE
SUBJECT OF PLANETARY SCIENCES FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY

Acknowledgements

To my parents, Mark and Melanie, and my brother, Alex, who have always supported and
encouraged me to follow my dreams and overcome all and any obstacles to achieve them.
To my grandparents, Anthony and Margery Wilson, Aubrey and Val Rolfe and Marjorie
and Russell Whitmore, this work is dedicated to you.
To Chris, my rock, without you I absolutely would not have been able to get through this
process. I would have had no clean clothes or fresh vegetables in my diet. You know how
much you mean to me, you are my best friend and your support means more to me than
you can know.
To Manish, Karen, Iain and Tim, my supervisors, thank you for your guidance and
instruction, especially on a multi-disciplinary project, where you taught me analytical
techniques and skills, and entirely new to me, microbiology. I could not have done this
without you.
Regardless of your walk of life - to those who may not realise their mental health is
suffering, every now and then take a moment to look up the symptoms of depression and if
you fit any of them, I encourage you to get help. Do not suffer alone.
Thank you to my examiners, Susana Jorge-Villar and Monica Grady, who made my viva
examination an enjoyable experience after a nerve-wracking build-up.
Unending thanks goes to Mabs Gilmour for help with many hours of GCMS analysis that
did not make it into this thesis, but from whom I learned a lot, plus instruction on chemical
preparation of samples, and, most importantly, general but necessary support – I could not
have got through this without you.
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Thank you to Simona Nicoara for help with GCMS analysis, Marc Davies for help with
basalt powder preparation, Michelle Higgins for basalt thin section preparation and chips
of basalt, Stephen Summers for extensive tutoring on microbiology work and confocal
microscopy, Sasha Verchovsky for custom glass work, Diane Johnson for conducting
FIB-SEM imaging, Heather Davis for preparing and conducting TEM images, and Igor
Kraev for information about the TEM sample preparation process, Gordon Imlach for
FEG-SEM imaging (unfortunately, this work did not go to plan), and Karen Guyler and
Beverley Bishop for their support and help.
To my colleagues and support base: Jon Mason, Euan Monaghan, Dan Dawson, Adam
Stevens, Feargus Abernethy, Felicity Williams, Kathryn McDermott, Michael Goodyear,
Jess Barnes, Rebecca Wolsey, Elliot Curtis-Harper, Pete Landsberg, Ben Dryer, Phillipa
Smith and the other CEI residents, JD Bodenan, Mohit Melwani Daswani, Natalie Starkey,
Louisa Preston, Tom Barrett, Roy Adkin, Zoë Ellery, Alex Barrett, Helen Davidge, Beth
Steer, Ian Franchi, Sally Jordan, Terry McGenity, Lewis Dartnell – thank you for your
friendship and help and collaboration and I wish the you all the best for the future.
To everyone in the Science Department at Beaumont School, but especially Karen,
Caroline and Rathi, you are all so fabulous and dedicated, I have nothing but the greatest
respect for you all and I miss working with you every day.
To my neglected friends, you know who you are, those I have known many years and those
who I have recently got to know. You have stood by me and put up with diminished
communications but were always there for me when I did get in contact, after many weeks
or months of radio silence. I love you and I am so grateful for you being in my life.

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N.B. As mentioned in Section 1.2.3, the term biomarker, biosignature and bioindicator are
interchangeable. However, since beginning this PhD project, biomarker and biosignature
now have more well-defined uses. At the time of publication, the term ‘biosignature’ refers
to evidence for life, extant or extinct; whereas ‘biomarker’ is more readily used in
medicine as indicators of disease and by geologists and geochemists when analysing
molecular fossils in crude oils and petroleum. Due to historical definitions biomarker is
used throughout this thesis, however, it is recommended that biosignature is used in future
astrobiology-related writing.

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Abstract

Evaporitic environments that could provide habitats for life exist on present day Mars, in
addition to Recurring Slope Lineae (RSL), which have been observed suggesting a briny liquid
in the subsurface with a seasonal occurrence at the surface. Life detection is the focus for
future missions, including use of the Raman Laser Spectrometer (RLS) instrument on board
the ESA ExoMars rover for this purpose. Martian simulation chambers were used to expose a
subset of the α-amino acids (AA) and halophilic (‘salt-loving’) microbes to the surface and
near surface environment. Post-exposure, the detectability of biological molecules with Raman
spectroscopy (where the Raman spectrum is the biomarker) was examined, with the intention
to inform future missions.
Results from this work suggest that a statistical method (independent of band intensity) should
be used to rigorously define a set of characteristic Raman bands to unambiguously identify
AA, a technique applicable to all biomolecules. Following exposure, both AA and halite
entombed archaeal halophiles survived a combination of simulated martian conditions, e.g.
freeze-thaw cycling resulted in a maximum of 20 % biomarker signal loss for AA. Halophilic
microbes survived UV exposure up to 3.5 sols, though with a complete biomarker signal loss.
However, cell counts and hence, survival in near surface, freeze-thaw conditions (indicative of
RSL conditions) remained similar to the control sample. Furthermore, the Raman biomarker
signal remained intact and detectable, regardless of a reduced intensity.
Importantly, for AA doped onto crushed basalt the Raman band biomarkers were lost, which
has major implications for the ExoMars rover which will crush rock samples before
examination with the RLS instrument. Future missions should be designed to examine samples
with the Raman spectroscopy instrument prior to any crushing to avoid destroying the
biomarker signal that could be used to imply the presence of life.
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Publications

As a result of this work the following manuscript was accepted for publication, upon
which Chapter 3 is based:
Rolfe, S. M.; Patel, M. R.; Gilmour, I.; Olsson, K. and Ringrose, T. J. (2016) Defining
Multiple Characteristic Raman Bands of α-Amino Acids as Biomarkers for Planetary
Missions Using a Statistical Method. Origins of Life and Evolution of Biospheres, 46,
323-346.

The following are conference presentations given as a result of work conducted throughout
this study:
Rolfe, S. M.; Patel, M. R.; Gilmour, I.; Olsson, K. and Ringrose, T. J. (2013). Detecting
biomarkers on Mars using Raman spectroscopy. In: Molecules and Life in Extremes: UK
Astrobiology Conference 2013 - (ASB5), 17-19 April 2013, Edinburgh, UK.
Rolfe, S. M.; Patel, M.; Gilmour, I.; Olsson, K.; Ringrose, T. J. and Cockell, C. (2012).
Raman spectroscopy of biologically relevant amino acids under martian conditions. In:
Astrobiology Science Conference 2012 Exploring Life: Past, Present, Near and Far, 16-20
April 2012, Atlanta, GA, USA.
Rolfe, S. M.; Patel, M. R.; Olsson, K.; Cockell, C. S. and Ringrose, T. J. (2011). Raman
spectroscopy of amino acids and other biomarkers on Mars. In: 11th European Workshop
on Astrobiology (Annual workshop of EANA), 11 - 14 July 2011, Cologne, Germany
(poster).
Rolfe, S. M.; Patel, M. R.; Ringrose, T. J. and Leese, M. R. (2011). Planetary simulation
and hypervelocity impact at the Open University. In: Exploring Mars Habitability, 13-15
June 2011, Lisbon, Portugal (poster).

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