CARBON ISOTOPIC SIGNATURES OF MICROBIAL LIPIDS IN GEOTHERMAL DEPOSITS: ELUCIDATING THERMOPHILIC ECOLOGY

Lead Research Organisation: University of Bristol
Department Name: Chemistry

Abstract

Understanding the origins and diversification of life represents one of the most challenging scientific endeavours. In such efforts, constraining the limits of life on Earth is vital, as is an understanding of the ecology of those organisms that can survive and even thrive in environments characterised by extremes of temperature, salinity or pH. Of particular interest are geothermal systems, populated by diverse and deeply-branching thermophilic bacteria and Archaea. Recently we have demonstrated that microbial lipids are powerful tools in assessing and reconstructing the microbiology of terrestrial hot springs. In this proposal we focus on elucidating the carbon isotopic signatures of the lipids of geothermal organisms. The use of lipid biomarkers in combination with stable isotope analysis is crucial to understanding microbial ecology, providing a direct link between microbial identity and biochemical processes.

Lipids are found in all living organisms, typically serving as energy sources and structural components of cell membranes. Often highly diagnostic, well-preserved in the geological record, and entrained with information on biological diversity, environmental conditions and post-depositional alteration history, these compounds are particularly attractive for early life and astrobiological investigations. Our past studies of biomarkers in geothermal deposits reveal a profound diversity of encapsulated lipids, which can be utilized to profile microbial community composition. However, a potential of microbialite-preserved lipids that was untapped by our previous work is their carbon isotopic composition; strong and highly unusual variations in lipid carbon isotope values were observed in a small subset of our data but lacked crucial contextual data (e.g. the carbon isotopic composition of dissolved inorganic carbon, DIC, in the pools). This remains an untapped source of information on thermophilic physiologies and ecology in the New Zealand Taupo Volcanic Zone and the silica deposits formed there. Such deposits are essential archives of past life and elucidating the controls on organic matter formation in such settings will allow a better interpretation of the OM assemblages preserved in them.

We will map the range of carbon isotope values and evaluate their reproducibility in various geothermal sites with differing physicochemical conditions and in different biofacies. By embedding this data in the context of thermal spring DIC carbon isotope values and recent microbiological community profiling based on molecular (DNA and RNA) approaches, we will resolve the origin of the unusual carbon isotopic compositions. This will greatly expand on our capacity to interpret biomarker carbon isotope values preserved in ancient silica sinters, providing crucial information on sources of lipid biomarkers, metabolism and trophic structure.

In this work, we will target a range of diagnostic compounds from well-characterized geothermal settings in the Taupo Volcanic Zone in New Zealand and explore the controls on the variation of carbon isotopic signatures, coupling our past biomarker-based interpretations to carbon isotopic analyses in order to achieve a better understanding of the biodiversity of geothermal environments and to unravel biogeochemical and ecological function. This work will advance our interpretation of biosignatures preserved in the rock record, providing insight into the evolution and ecology of the earliest life-forms on Earth and informing the search for life elsewhere in the Solar System.

Planned Impact

Our basic objective to investigate organic signatures in geothermal systems will provide fundamental knowledge for microbiologists, Earth scientists and geochemists. Investigations into thermophilic ecology and biogeochemical processes through isotopic compositions of lipid biomarkers will be invaluable in the field of microbiology - diagnostic lipid biomarkers together with carbon isotopic compositions are powerful tools in assessing composition and metabolism of diverse microbial communities. In addition, the assessment of preservation of lipid biomarkers and their isotopes in mineral deposits will enhance interpretation of biosignatures in the geological record with biomarker investigations of ancient deposits proving useful in palaeoecological studies. Overall, this work will facilitate interdisciplinary research that will result in enhanced understanding across the academic community of the evolution and ecology of geothermal systems.

Planetary scientists have discovered extraterrestrial hydrothermal systems, and such sites have become high priority targets in the search for life beyond Earth. Terrestrial analogues of these sites therefore play a key role in astrobiology. Our study will enhance the understanding of the ecology of terrestrial geothermal systems, providing vital information for planning exploration missions and the interpretation of the data they retrieve.

Further impact will arise from potential biotechnological benefits in characterizing these unusual biochemicals. For example, since these lipids control and maintain the integrity of the membranes of thermophiles and acidophiles, they could also serve as the platform for designing particularly stable liposomes for drug delivery. Thus the impact of this work is fundamental, interdisciplinary and potentially far reaching.

Outside of academia, extreme environments and their unusual inhabitants are of great interest to the general public. The University of Bristol has numerous public engagement and outreach activities, including the Bristol ChemLabS Outreach programme (engaging with ca. 30,000 people per year) and the Bristol Festival of Nature (engaging with ca. 30,000 people over one weekend). By linking to these established programmes and developing our own engagement agenda (including workshops, game development, lecturettes and articles in science education magazines), we will communicate this research to the general public.
 
Description Carbon isotopic compositions of lipids encapsulated in geothermal deposits are highly variable and in some cases unusually high, reflecting the metabolic pathways employed by source organisms. This has a variety for implications. For example, organic matter found on the early Earth or other planets and produced by geothermal organisms could have highly unusual isotopic compositions and be incorrectly attributed to a non-biological origin
Exploitation Route Our investigation of lipid signatures in geothermal systems can be applied to paleoenvironmental, origin of life and astrobiological investigations.

Identification of viable target compounds for exobiological investigations will guide exploration instrumentation development with respect to detection of specific compound classes. Our findings can be used in defining the range of compound and isotopic signatures likely to be detected and aid in the interpretation of these organic signatures.
Sectors Environment

 
Description Our findings are a central part of the School of Chemistry's public and school engagement. Understanding the origins, nature and wider persistence of life is of the widest cultural and societal interest, informing our perspectives on the past and future of our species and helping to define our unique (or not) role in the cosmos. As such, interest in the extremes of life is of profound: how can organisms acquire energy, and what are the tolerances of terrestrial life for extremes of temperature, pH or pressure. This work is exceptionally popular in exciting 6th form students about the wider possibilities of science and informing the general public about the persistence of life.
First Year Of Impact 2014
Sector Education
Impact Types Cultural

Societal

 
Description Malta Schools Science Week 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Schools
Results and Impact Approx. 380 pupils attended a range of science talks and presentations during the NSTF Science Expo Week in Malta.

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Year(s) Of Engagement Activity 2014
 
Description School visit to Farnborough Air Show 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact Approx. 30 school pupils attended talks at the UK Space Agency stand at Farnborough Air Show, in support of a visit from astronaut Tim Peake.

n/a
Year(s) Of Engagement Activity 2014
 
Description School visits 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Schools
Results and Impact Students visiting the School of Chemistry attended talks on current research, leading to questions and short discussions after the presentations.

The presentations sparked interest in current research in the chemical sciences.
Year(s) Of Engagement Activity 2014
 
Description Teacher training event 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact Teachers on a teacher training course at the University of Bristol attended a presentation on contemporary topics in the chemical sciences.

Teachers are able to inform students of current research being undertaken at the University.
Year(s) Of Engagement Activity 2014