Argumentation that supports the use of this feature as a biosignature based on biological prevalence.
PRO arguments and evidence highlight the presence of the feature in and/or due to life. CON arguments and evidence highlight how biological prevalence cannot justify the use of this feature as a biosignature.
Biological Signal Strength - Background
Argumentation that supports the use of this feature as a biosignature based on signal strength.
PRO arguments and evidence highlight the strength of signals such abundance, rate, structure, patterns, and intensity to be indicative of life. CON arguments and evidence highlight how the strength of specific signals are not justifications to support a biological origin.
Abiotic Prevalence - Background
Argumentation that refutes the use of this feature as a biosignature due to abiotic prevalence.
PRO arguments and evidence highlight the presence of the feature due to abiotic processes. CON arguments and evidence highlight how abiotic prevalence cannot refute the use of this feature as a biosignature.
Abiotic Signal Strength - Background
Argumentation that refutes the use of this feature as a biosignature based on signal strength of abiotic processes.
PRO arguments and evidence highlight the strength of signals such abundance, rate, structure, patterns, and intensity to be caused by abiotic processes. CON arguments and evidence highlight how the strength of specific signals from abiotic processes do not refute a potential biological origin.
Fatty acids with a characteristic distribution of chain lengths that roughly span 30 Å (~C10 - 20) form stable membrane bilayers functional for life.
[General]
Lipid headgroup-specific acyl chain remodeling is a mechanism for fine-tuning the membrane’s physical state
Lipid headgroup-specific acyl chain remodeling as a mechanism for fine-tuning the membrane’s physical state
Evidence is Sourced from:
Title
Principles of membrane adaptation revealed through environmentally induced bacterial lipidome remodeling.
Authors
Chwastek G, Surma MA, Rizk S, Grosser D, Lavrynenko O, Ruchiánska M, Jambor H, Sáenz J.
Abstract
Cells, from microbes to mammals, adapt their membrane lipid composition in response to environmental changes to maintain optimal properties. Global patterns of lipidome remodeling are poorly understood, particularly in organisms with simple lipid compositions that can provide insight into fundamental principles of membrane adaptation. Using shotgun lipidomics, we examine the simple yet, as we show here, adaptive lipidome of the plant-associated Gram-negative bacterium Methylobacterium extorquens. We observe that minimally 11 lipids account for 90% of total variability, thus constraining the upper limit of variable lipids required for an adaptive living membrane. Through lipid features analysis, we reveal that acyl chain remodeling is not evenly distributed across lipid classes, resulting in headgroup-specific effects of acyl chain variability on membrane properties. Results herein implicate headgroup-specific acyl chain remodeling as a mechanism for fine-tuning the membrane’s physical state and provide a resource for using M. extorquens to explore the design principles of living membranes.
Membranes can be formed from amphiphilic biomolecules other than normal-chain fatty acids (e.g., isoprenoid lipids, peptides, other biomolecules).
[General]
Membrane bilayers in Archaea are composed of isoprenoid lipids
Membrane bilayers in Archaea are composed of C20 or C25 isoprenoid alkyl chains in ether linkage to the glycerol backbone. Some archaea contain diglycerol-tetraether polar lipids with two C40 isoprenoid chains spanning the hydrophobic inner core of the bilayer. Archaea are a major domain of microbial life
Evidence is Sourced from:
Title
Liquid but Durable: Molecular Dynamics Simulations Explain the Unique Properties of Archaeal-Like Membranes
Archaeal plasma membranes appear to be extremely durable and almost impermeable to water and ions, in contrast to the membranes of Bacteria and Eucaryota. Additionally, they remain liquid within a temperature range of 0–100°C. These are the properties that have most likely determined the evolutionary fate of Archaea and it may be possible for bionanotechnology to adopt these from nature. In this work, we use molecular dynamics simulations to assess at the atomistic level the structure and dynamics of a series of model archaeal membranes with lipids that have tetraether chemical nature and “branched” hydrophobic tails. We conclude that the branched structure defines dense packing and low water permeability of archaeal-like membranes, while at the same time ensuring a liquid-crystalline state, which is vital for living cells. This makes tetraether lipid systems promising in bionanotechnology and material science, namely for design of new and unique membrane nanosystems.
Short peptides form structural and functional bilayer membranes.
Peptide bilayers can be exploited for the construction of lipid-like nanomaterials with protein functionality.
Evidence is Sourced from:
Title
Peptides Organized as Bilayer Membranes.
Authors
Childers WS, Mehta AK, Ni R, Taylor JV, Lynn DG
Abstract
A buried polar bilayer interface composed of interdigitated peptide ends and a high density of CF3COO− counterions passifying lysine amines are identified in nanotubes obtained by self-assembly of short peptides. The structure reveals distinct characteristics that differentiate peptide bilayers and lipid bilayers that can now be exploited for the construction of lipid-like nanomaterials with protein functionality.
The second major biomass component on Earth is bacteria (≈70 Gt), constituting ≈15% of the global biomass.
The second major biomass component on Earth is bacteria (≈70 Gt), constituting ≈15% of the global biomass.
Evidence is Sourced from:
Title
The biomass distribution on Earth.
Authors
Bar-on YM, Phillips R, Milo R
Abstract
A census of the biomass on Earth is key for understanding the structure and dynamics of the biosphere. However, a global, quantitative view of how the biomass of different taxa compare with one another is still lacking. Here, we assemble the overall biomass composition of the biosphere, establishing a census of the ≈550 gigatons of carbon (Gt C) of biomass distributed among all of the kingdoms of life. We find that the kingdoms of life concentrate at different locations on the planet; plants (≈450 Gt C, the dominant kingdom) are primarily terrestrial, whereas animals (≈2 Gt C) are mainly marine, and bacteria (≈70 Gt C) and archaea (≈7 Gt C) are predominantly located in deep subsurface environments. We show that terrestrial biomass is about two orders of magnitude higher than marine biomass and estimate a total of ≈6 Gt C of marine biota, doubling the previous estimated quantity. Our analysis reveals that the global marine biomass pyramid contains more consumers than producers, thus increasing the scope of previous observations on inverse food pyramids. Finally, we highlight that the mass of humans is an order of magnitude higher than that of all wild mammals combined and report the historical impact of humanity on the global biomass of prominent taxa, including mammals, fish, and plants.
eIntact polar lipids containing fatty acids are rapidly degraded after cell death by the cell’s own lytic enzymes or those of decomposers (heterotrophs).
Intact polar lipids containing fatty acids are rapidly degraded after cell death by the cell’s own lytic enzymes or those of decomposers (heterotrophs).
Intact polar lipids containing fatty acids are rapidly degraded after cell death by the cell’s own lytic enzymes or those of decomposers (heterotrophs).
Evidence is Sourced from:
Title
Lipids in Plants and Microbes
Authors
Harwood JL, Russell NJ
Abstract
This short text is designed to provide basic information about plant and microbial lipids not only for scientists working in the microbiological and plant fields, but for anyone wanting a concise introduction to this aspect of lipid biochemistry. We have long been aware that standard biochemistry books tend to. concentrate (sometimes exclusively) on animal lipids, thus neglecting many of the important and special features of other organisms. It is not our intention that the book should be comprehensive and we have not, for instance, provided complete lists of lipid compositions of all plants and bacterial species; a number of excellent specialist texts exist and many of these are listed for further reading. Instead we have sought to provide sufficient information for an advanced undergraduate or a research student to give them a 'feel' for the subject. By a combination of generalisation and the use of examples of special interest we hope the book will whet the appetite of the reader so that, by their own research, they are stimulated to discover and, perhaps, answer some of the fascinating questions concerning plant and microbial lipids. We trust that we shall succeed in these aims, even if that will mean more competition for research funds in our own fields! J. L. HARWOOD N. J. RUSSELL November 1983 Acknowledgements Our research careers have been devoted to a study of lipids: we have no regrets and are happy to acknowledge Professors J. N.
eThe distribution of chain lengths of carboxylic acids in the Murchison meteorite has not been fully characterized and may overlap biotic chain lengths and patterns.
The distribution of chain lengths of carboxylic acids in the Murchison meteorite has not been fully characterized and may overlap biotic chain lengths and patterns.
The distribution of chain lengths of carboxylic acids in the Murchison meteorite has not been fully characterized and may overlap biotic chain lengths and patterns.
Evidence is Sourced from:
Title
Molecular and compound-specific isotopic characterization of monocarboxylic acids in carbonaceous meteorites.
Authors
Huang Y, Wang Y, Alexandre MR, Lee T, Rose-Petruck C, Fuller M, Pizzarello S
Abstract
Low molecular weight monocarboxylic acids are the most abundant water soluble organic compounds in the Murchison and many other CM type carbonaceous chondrites. In this study, we examined the monocarboxylic acids in Murchison and EET96029.20 carbonaceous meteorites using a new sample preparation and introduction technique for gas chromatograph recently developed for volatile, water-soluble organic compounds: solid phase micro-extraction (SPME). We identified more than 50 monocarboxylic acids from Murchison compared with the 18 compounds reported previously. Formic acid, a known interstellar molecule, has been fully analyzed in these carbonaceous meteorites, with its δD value suggesting an interstellar origin. We determined both carbon and hydrogen isotopic ratios of individual monocarboxylic acids in Murchison, to better define the origins and genetic relationships of these compounds. The compound-specific isotopic data reveal a large enrichment in 13C (δ13C up to + 32.5‰) and particularly D (δD up to + 2024‰). The branched acids are substantially enriched in both 13C and D relative to the straight chain acids, with those branched acids containing a quaternary carbon showing the greatest isotopic enrichment. The isotopic difference may be attributed to variations in the different synthetic regimes or terrestrial input of straight chain acids.
eThe carboxylic acid compound group comprises significantly more molecular species than those unequivocally identified in the Tagish Lake and Murchison meteorites.
The carboxylic acid compound group comprises significantly more molecular species than those unequivocally identified in the Tagish Lake and Murchison meteorites.
The carboxylic acid compound group comprises significantly more molecular species than those unequivocally identified in the Tagish Lake and Murchison meteorites.
Evidence is Sourced from:
Title
The nature and distribution of the organic material in carbonaceous chondrites and interplanetary dust particles.
Authors
Pizzarello S, Cooper GW, Flynn GJ
Abstract
Most of the carbon in carbonaceous chondrites is organic material that displays structures
as diverse as kerogen-like macromolecules and simpler soluble compounds ranging from polar
amino acids and polyols to nonpolar hydrocarbons. Overall, the large molecular and isotopic
diversity of meteorite organics verifies their extraterrestrial origin and points to synthetic pathways in a variety of chemical regimes. These include exothermic reactions in the cold, H-fractionating interstellar gas phase and aqueous reactions in asteroidal parent bodies. Reactions on interstellar grains and during nebular processes were most likely involved but are inferred with less certainty. The unique L-asymmetry of some meteoritic amino acids suggests their possible contribution to terrestrial molecular evolution. Many interplanetary dust particles show a primitive composition that distinguishes them from known meteorites and could offer unique insights into unaltered nebular material. So far, micrometer sizes have prevented their wide-ranging molecular characterization.
Abiotic Fischer-Tropsch synthesis produces fatty acids with a Poisson-like distribution in their carbon chain length number.
Abiotic Fischer-Tropsch synthesis produces fatty acids with a Poisson-like distribution in their carbon chain length number, with a maximum of “short fatty acids” at a length of 7 to 10 carbon atoms and decreasing abundance of fatty acid chains above 15 carbon atoms.
Evidence is Sourced from:
Title
Molecular and compound-specific isotopic characterization of monocarboxylic acids in carbonaceous meteorites
Authors
Huang ., Wang Y, Alexandre MR, Lee T, Rose-Petruck C, Fuller M, Pizzarello S
Abstract
Low molecular weight monocarboxylic acids are the most abundant water soluble organic compounds in the Murchison and many other CM type carbonaceous chondrites. In this study, we examined the monocarboxylic acids in Murchison and EET96029.20 carbonaceous meteorites using a new sample preparation and introduction technique for gas chromatograph recently developed for volatile, water-soluble organic compounds: solid phase micro-extraction (SPME). We identified more than 50 monocarboxylic acids from Murchison compared with the 18 compounds reported previously. Formic acid, a known interstellar molecule, has been fully analyzed in these carbonaceous meteorites, with its δD value suggesting an interstellar origin. We determined both carbon and hydrogen isotopic ratios of individual monocarboxylic acids in Murchison, to better define the origins and genetic relationships of these compounds. The compound-specific isotopic data reveal a large enrichment in 13C (δ13C up to + 32.5‰) and particularly D (δD up to + 2024‰). The branched acids are substantially enriched in both 13C and D relative to the straight chain acids, with those branched acids containing a quaternary carbon showing the greatest isotopic enrichment. The isotopic difference may be attributed to variations in the different synthetic regimes or terrestrial input of straight chain acids.
Carboxylic acids and other amphiphilic compounds in carbonaceous chondrites are capable of forming membrane bilayers that may mimic life.
Carboxylic acids and other amphiphilic compounds in carbonaceous chondrites are capable of forming membrane bilayers that may mimic life.
Evidence is Sourced from:
Title
Amphiphilic components of the Murchison carbonaceous chondrite: surface properties and membrane formation.
Authors
Deamer, D. W. & Pashley, R. M.
Abstract
We have investigated physicochemical properties of amphiphilic compounds in carbonaceous meteorites. The primary aim was to determine whether such materials represent plausible sources of lipid-like compounds that could have been involved as membrane components in primitive cells. Samples of the Murchison CM2 chondrite were extracted with chloroform-methanol, and the chloroform-soluble material was separated by two-dimensional thin layer chromatography. Fluorescence, iodine stains and charring were used to identify major components on the plates. These were then scraped and eluted as specific fractions which were investigated by fluorescence and absorption spectra, surface chemical methods, gas chromatography-mass spectrometry, and electron microscopy. Fraction 5 was strongly fluorescent, and contained pyrene and fluoranthene, the major polycyclic aromatic hydrocarbons of the Murchison chondrite. This fraction was also present in extracts from the Murray and Mighei CM2 chondrites. Fraction 3 was surface active, forming apparent monomolecular films at air-water interfaces. Surface force measurements suggested that fraction 3 contained acidic groups. Fraction 1 was also surface active, and certain components could self-assemble into membranous vesicles which encapsulated polar solutes. The observations reported here demonstrate that organic compounds plausibly available on the primitive Earth through meteoritic infall are surface active, and have the ability to self-assemble into membranes.
Amphiphilic oxidized polycyclic aromatic hydrocarbons (PAH) derivatives in a simulated prebiotic membrane exhibit cholesterol-like stabilizing effect.
Amphiphilic oxidized PAH derivatives in a simulated prebiotic membrane exhibit cholesterol-like stabilizing effect.
Evidence is Sourced from:
Title
Polycyclic Aromatic Hydrocarbons as Plausible Prebiotic Membrane Components
Authors
Groen J., Deamer D.W., Kros A., and Ehrenfreund P.
Abstract
Aromatic molecules delivered to the young Earth during the heavy bombardment phase in the early history of our solar system were likely to be among the most abundant and stable organic compounds available. The Aromatic World hypothesis suggests that aromatic molecules might function as container elements, energy transduction elements and templating genetic components for early life forms. To investigate the possible role of aromatic molecules as container elements, we incorporated different polycyclic aromatic hydrocarbons (PAH) in the membranes of fatty acid vesicles. The goal was to determine whether PAH could function as a stabilizing agent, similar to the role that cholesterol plays in membranes today. We studied vesicle size distribution, critical vesicle concentration and permeability of the bilayers using C6-C10 fatty acids mixed with amphiphilic PAH derivatives such as 1-hydroxypyrene, 9-anthracene carboxylic acid and 1,4 chrysene quinone. Dynamic Light Scattering (DLS) spectroscopy was used to measure the size distribution of vesicles and incorporation of PAH species was established by phase-contrast and epifluorescence microscopy. We employed conductimetric titration to determine the minimal concentration at which fatty acids could form stable vesicles in the presence of PAHs. We found that oxidized PAH derivatives can be incorporated into decanoic acid (DA) vesicle bilayers in mole ratios up to 1:10 (PAH:DA). Vesicle size distribution and critical vesicle concentration were largely unaffected by PAH incorporation, but 1-hydroxypyrene and 9-anthracene carboxylic acid lowered the permeability of fatty acid bilayers to small solutes up to 4-fold. These data represent the first indication of a cholesterol-like stabilizing effect of oxidized PAH derivatives in a simulated prebiotic membrane.
Due to the low weathering rate on Mars, significant accumulations of meteorites per square kilometer are possible.
Due to the low weathering rate on Mars, significant accumulations of ca. 5x10^2 to 5x10^5 meteorites greater than 10g in mass per square kilometer are possible.
Evidence is Sourced from:
Title
Meteorite Accumulations on Mars
Authors
Bland PA, Smith TB
Abstract
We have modeled single-body meteoroid atmospheric entry speeds at Mars and the effect of drag and ablation, and identify a narrow range of small masses (10–50 g) that should impact Mars at survivable speeds. The rate of oxidative weathering is much lower than that on Earth, so this small flux of meteorites could give rise to significant accumulations: ca. 5×102 to 5×105 meteorites greater than 10 g in mass per square kilometer. Given that extremely large numbers of meteorites may be present on Mars, future sample-return missions should consider the real possibility that they may recover meteoritic material. Due to the low weathering rate, meteorites may survive on the surface of Mars for more than 109 years, preserving a record of the temporal variability of the meteoroid flux and the compositional evolution of the meteoroid complex. Intact carbonaceous chondrites may also preserve organic compounds from degradation by ultraviolet radiation. Terrestrial meteorites may be present, but would probably be sterile.
Intact carbonaceous chondrites on the surface of the planet may also preserve organic compounds from degradation by ultraviolet radiation.
Organic compounds in the interior of carbonaceous chondritesIntact can be protected from UV and gamma radiation, which can directly destroy them.
Evidence is Sourced from:
Title
Meteorite Accumulations on Mars
Authors
Bland P.A., Smith T.B.
Abstract
We have modeled single-body meteoroid atmospheric entry speeds at Mars and the effect of drag and ablation, and identify a narrow range of small masses (10–50 g) that should impact Mars at survivable speeds. The rate of oxidative weathering is much lower than that on Earth, so this small flux of meteorites could give rise to significant accumulations: ca. 5×102 to 5×105 meteorites greater than 10 g in mass per square kilometer. Given that extremely large numbers of meteorites may be present on Mars, future sample-return missions should consider the real possibility that they may recover meteoritic material. Due to the low weathering rate, meteorites may survive on the surface of Mars for more than 109 years, preserving a record of the temporal variability of the meteoroid flux and the compositional evolution of the meteoroid complex. Intact carbonaceous chondrites may also preserve organic compounds from degradation by ultraviolet radiation. Terrestrial meteorites may be present, but would probably be sterile.
Irradiation of perchlorate on the Martian surface produces reactive intermediates that destroy organics
When perchlorate salts are exposed to gamma and UV radiation on the surface of Mars, they decompose in a CO2 atmosphere to form hypochlorite (ClO−), trapped oxygen (O2), and chlorine dioxide (ClO2). These reactive intermediates destroy organic compounds, and their presence are thought to explain the results of the Viking biology experiments.
Evidence is Sourced from:
Title
Perchlorate Radiolysis on Mars and the Origin of Martian Soil Reactivity
Authors
Quinn R.C., Martucci H., Miller S.R., Bryson C.E., Grunthaner F.J., Grunthaner P.
Abstract
Results from the Viking biology experiments indicate the presence of reactive oxidants in martian soils that have previously been attributed to peroxide and superoxide. Instruments on the Mars Phoenix Lander and the Mars Science Laboratory detected perchlorate in martian soil, which is nonreactive under the conditions of the Viking biology experiments. We show that calcium perchlorate exposed to gamma rays decomposes in a CO2 atmosphere to form hypochlorite (ClO−), trapped oxygen (O2), and chlorine dioxide (ClO2). Our results show that the release of trapped O2 (g) from radiation-damaged perchlorate salts and the reaction of ClO− with amino acids that were added to the martian soils can explain the results of the Viking biology experiments. We conclude that neither hydrogen peroxide nor superoxide is required to explain the results of the Viking biology experiments.
Patterns in carboxylic acids, or fatty acids, can be useful in determining the origin (biotic or abiotic) of organic material. Carboxylic acids consist of a hydrocarbon chain with a carboxylic acid functional group on one end. Fatty acids are universal components of bacterial and eukaryotic membranes, but they can also be synthesized abiotically. Fatty acids in living organisms are commonly found esterified to other molecules, however they can also be found as “free” fatty acids in the environment. Fatty acids are major components of phospholipids which are a major component of the lipid bilayers which form the membranes delineating and protecting a cell from its environment. Fatty acids are also used for energy storage. Organisms have evolved pathways for the biosynthesis of fatty acids and also for oxidation for energy. The biosynthetic pathways result in fatty acid patterns with specific carbon number features and stable carbon isotopic composition that allow them to be distinguishable [read more]Patterns in carboxylic acids, or fatty acids, can be useful in determining the origin (biotic or abiotic) of organic material. Carboxylic acids consist of a hydrocarbon chain with a carboxylic acid functional group on one end. Fatty acids are universal components of bacterial and eukaryotic membranes, but they can also be synthesized abiotically. Fatty acids in living organisms are commonly found esterified to other molecules, however they can also be found as “free” fatty acids in the environment. Fatty acids are major components of phospholipids which are a major component of the lipid bilayers which form the membranes delineating and protecting a cell from its environment. Fatty acids are also used for energy storage. Organisms have evolved pathways for the biosynthesis of fatty acids and also for oxidation for energy. The biosynthetic pathways result in fatty acid patterns with specific carbon number features and stable carbon isotopic composition that allow them to be distinguishable from their abiotic counterparts. These patterns are easily distinguishable using analytical methods that are capable of chemically separating and characterizing the molecular structures of the fatty acids (such as gas-chromatography and mass spectrometry, etc.).
Abiotic Fischer-Tropsch syntheses produce fatty acids with a Poisson-like distribution in their carbon chain length number, with a maximum of “short fatty acids” at a length of 7 to 10 carbon atoms and decreasing abundance of fatty acid chains above 15 carbon atoms. Conversely, bacterial systems produce certain fatty acids in excess, typically resulting in a bimodal distribution with two maxima. This signal can be preserved over geological timescales. The molecular dimensions of these two maxima correspond to the biotic systems specific fatty acid requirements for functional cell membranes. Fatty acid biosynthesis is remarkably similar in microorganisms, plants and animals. Acetyl-coenzyme A is used as a primer with sequential addition of C2 units provided by malonyl-CoA.The result is that even numbered carbon fatty acids, palmitic and stearic acid with 16 and 18 carbon atoms, respectively, are the dominant fatty acid in most bacteria generally in a range from 16 to 20 carbon atoms. Biosynthesis of odd numbered carbon chains is initiated with an odd carbon primer, e.g. propionyl-CoA. Some bacteria also biosynthesize terminally branched fatty acids (iso- and anteiso-) by elongating a branched short chain acyl-CoA primer. Most bacteria exhibit an even carbon chain length preference, yet for many bacteria have with branched fatty acids, an odd carbon chain length predominance can result. This preference for either even or odd numbers of carbons in their chains is absent from the fatty acids produced by the abiotic Fischer-Tropsch syntheses, as carbon atoms are added one at a time. Chain-length preference is found to be preserved in ancient sediments but is often lost over time as the biogenic material undergoes thermal maturation processes. This so-called carbon preference index (CPI) is used to assess the maturity of oil and source rocks. The CPI of Fischer-Tropsch type syntheses of fatty acids around one.