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Life
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The Physico-Chemical Limits of Life
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The Physico-Chemical Limits of Life

A special issue of Life (ISSN 2075-1729). This special issue belongs to the section "Hypotheses in the Life Sciences".

Deadline for manuscript submissions: closed (30 June 2016) | Viewed by 70046

Special Issue Editors

Prof. Dr. John A. Baross

E-Mail Website
Guest Editor
School of Oceanography, University of Washington, Box 357940, Seattle, WA 98195, USA
Interests: life in estreme environments; limits of life; the origin and evolution of life on Earth; astrobiology and the search for life elsewhere
Dr. William Bains

E-Mail Website
Guest Editor
1. Five Alarm Bio Ltd., Cambridge CB22 5HX, UK
2. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Interests: astrobiology; detection of life; limits of life; origin of life; nature of aging; anti-aging medicine; computational chemistry; science commercialization; biotechnology financing; venture capital

Special Issue Information

Dear Colleagues,

The vast majority of life on Earth lives at between 0.75 and 5 bar pressure and –5 oC and 30 oC temperature. However, we know that life can flourish substantially outside these limits. Recent decades have shown that life in the deep ocean, in hydrothermal systems or in crustal rocks may play a substantial role in the chemistry of Earth’s biosphere, and the discovery of a bewildering variety of planets around other stars suggest environments very different from Earth’s where we might nevertheless look for life. They have also shown that the abundant chemical and energy resources of the surface are not essential for life, and that cells with doubling times may in future decades grow in regions previously considered incapable of supporting metabolism. Our knowledge on the limits of life on Earth continues to expand as we explore more remote and seemingly inhospitable environments using advanced technologies. Laboratory experiments and theoretical studies hint that life could be based on molecular structures substantially different from those we know. So what are the physico–chemical limits of the environments in which any life, not just common terrestrial life, can flourish? This Special Issue explores these questions with the aim of increasing our knowledge about the fundamental nature of living beings (known or yet to be discovered by science), and also launches a new Section of Life—Life: Hypotheses in the Life Sciences. Life: HyLS will focus on new ideas, hypotheses and theoretical approaches to problems in the life sciences, starting with the question: What are the physico–chemical limits of life? The answers will inform where we search for life on Earth and elsewhere, but also synthetic attempts to build new life with useful capabilities.

Prof. Dr. John A. Baross
Dr. William Bains
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Life is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • alternative biochemistry
  • artificial life
  • bioenergetics
  • biological energy quantum
  • extremophiles
  • stability
  • synthetic biology
  • thermodynamics
  • macromolecular structure
  • LUCA

Published Papers (6 papers)

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Editorial

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353 KiB  
Editorial
Hypotheses, Limits, Models and Life
by William Bains
Life 2015, 5(1), 1-3; https://doi.org/10.3390/life5010001 - 29 Dec 2014
Cited by 4 | Viewed by 4891
Abstract
Life is launching a new section, called Hypotheses in the Life Sciences. The new Section will complement the other sections of Life, providing a feedstock of ideas whose tests can be published in the wider Life family, and elsewhere. We will [...] Read more.
Life is launching a new section, called Hypotheses in the Life Sciences. The new Section will complement the other sections of Life, providing a feedstock of ideas whose tests can be published in the wider Life family, and elsewhere. We will consider hypotheses that are supported by real world, rigorous evidence, by clear arguments, and which provide a potential solution to a genuine gap in our understanding of any aspect of the life sciences. Full article
(This article belongs to the Special Issue The Physico-Chemical Limits of Life)

Research

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8800 KiB  
Article
Prediction of the Maximum Temperature for Life Based on the Stability of Metabolites to Decomposition in Water
by William Bains, Yao Xiao and Changyong Yu
Life 2015, 5(2), 1054-1100; https://doi.org/10.3390/life5021054 - 26 Mar 2015
Cited by 22 | Viewed by 6644
Abstract
The components of life must survive in a cell long enough to perform their function in that cell. Because the rate of attack by water increases with temperature, we can, in principle, predict a maximum temperature above which an active terrestrial metabolism cannot [...] Read more.
The components of life must survive in a cell long enough to perform their function in that cell. Because the rate of attack by water increases with temperature, we can, in principle, predict a maximum temperature above which an active terrestrial metabolism cannot function by analysis of the decomposition rates of the components of life, and comparison of those rates with the metabolites’ minimum metabolic half-lives. The present study is a first step in this direction, providing an analytical framework and method, and analyzing the stability of 63 small molecule metabolites based on literature data. Assuming that attack by water follows a first order rate equation, we extracted decomposition rate constants from literature data and estimated their statistical reliability. The resulting rate equations were then used to give a measure of confidence in the half-life of the metabolite concerned at different temperatures. There is little reliable data on metabolite decomposition or hydrolysis rates in the literature, the data is mostly confined to a small number of classes of chemicals, and the data available are sometimes mutually contradictory because of varying reaction conditions. However, a preliminary analysis suggests that terrestrial biochemistry is limited to environments below ~150–180 °C. We comment briefly on why pressure is likely to have a small effect on this. Full article
(This article belongs to the Special Issue The Physico-Chemical Limits of Life)
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Review

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601 KiB  
Review
Halophilic Archaea: Life with Desiccation, Radiation and Oligotrophy over Geological Times
by Helga Stan-Lotter and Sergiu Fendrihan
Life 2015, 5(3), 1487-1496; https://doi.org/10.3390/life5031487 - 28 Jul 2015
Cited by 58 | Viewed by 12669
Abstract
Halophilic archaebacteria (Haloarchaea) can survive extreme desiccation, starvation and radiation, sometimes apparently for millions of years. Several of the strategies that are involved appear specific for Haloarchaea (for example, the formation of halomucin, survival in fluid inclusions of halite), and some are known [...] Read more.
Halophilic archaebacteria (Haloarchaea) can survive extreme desiccation, starvation and radiation, sometimes apparently for millions of years. Several of the strategies that are involved appear specific for Haloarchaea (for example, the formation of halomucin, survival in fluid inclusions of halite), and some are known from other prokaryotes (dwarfing of cells, reduction of ATP). Several newly-discovered haloarchaeal strategies that were inferred to possibly promote long-term survival—halomucin, polyploidy, usage of DNA as a phosphate storage polymer, production of spherical dormant stages—remain to be characterized in detail. More information on potential strategies is desirable, since evidence for the presence of halite on Mars and on several moons in the solar system increased interest in halophiles with respect to the search for extraterrestrial life. This review deals in particular with novel findings and hypotheses on haloarchaeal long-term survival. Full article
(This article belongs to the Special Issue The Physico-Chemical Limits of Life)
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Other

1724 KiB  
Concept Paper
Pressure as a Limiting Factor for Life
by Rachael Hazael, Filip Meersman, Fumihisa Ono and Paul F. McMillan
Life 2016, 6(3), 34; https://doi.org/10.3390/life6030034 - 17 Aug 2016
Cited by 20 | Viewed by 6145
Abstract
Facts concerning the stability and functioning of key biomolecular components suggest that cellular life should no longer be viable above a few thousand atmospheres (200–300 MPa). However, organisms are seen to survive in the laboratory to much higher pressures, extending into the GPa [...] Read more.
Facts concerning the stability and functioning of key biomolecular components suggest that cellular life should no longer be viable above a few thousand atmospheres (200–300 MPa). However, organisms are seen to survive in the laboratory to much higher pressures, extending into the GPa or even tens of GPa ranges. This is causing main questions to be posed concerning the survival mechanisms of simple to complex organisms. Understanding the ultimate pressure survival of organisms is critical for food sterilization and agricultural products conservation technologies. On Earth the deep biosphere is limited in its extent by geothermal gradients but if life forms exist in cooler habitats elsewhere then survival to greater depths must be considered. The extent of pressure resistance and survival appears to vary greatly with the timescale of the exposure. For example, shock experiments on nanosecond timescales reveal greatly enhanced survival rates extending to higher pressure. Some organisms could survive bolide impacts thus allowing successful transport between planetary bodies. We summarize some of the main questions raised by recent results and their implications for the survival of life under extreme compression conditions and its possible extent in the laboratory and throughout the universe. Full article
(This article belongs to the Special Issue The Physico-Chemical Limits of Life)
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4498 KiB  
Concept Paper
Titan as the Abode of Life
by Christopher P. McKay
Life 2016, 6(1), 8; https://doi.org/10.3390/life6010008 - 03 Feb 2016
Cited by 41 | Viewed by 15476
Abstract
Titan is the only world we know, other than Earth, that has a liquid on its surface. It also has a thick atmosphere composed of nitrogen and methane with a thick organic haze. There are lakes, rain, and clouds of methane and ethane. [...] Read more.
Titan is the only world we know, other than Earth, that has a liquid on its surface. It also has a thick atmosphere composed of nitrogen and methane with a thick organic haze. There are lakes, rain, and clouds of methane and ethane. Here, we address the question of carbon-based life living in Titan liquids. Photochemically produced organics, particularly acetylene, in Titan’s atmosphere could be a source of biological energy when reacted with atmospheric hydrogen. Light levels on the surface of Titan are more than adequate for photosynthesis, but the biochemical limitations due to the few elements available in the environment may lead only to simple ecosystems that only consume atmospheric nutrients. Life on Titan may make use of the trace metals and other inorganic elements produced by meteorites as they ablate in its atmosphere. It is conceivable that H2O molecules on Titan could be used in a biochemistry that is rooted in hydrogen bonds in a way that metals are used in enzymes by life on Earth. Previous theoretical work has shown possible membrane structures, azotosomes, in Titan liquids, azotosomes, composed of small organic nitrogen compounds, such as acrylonitrile. The search for a plausible information molecule for life in Titan liquids remains an open research topic—polyethers have been considered and shown to be insoluble at Titan temperatures. Possible search strategies for life on Titan include looking for unusual concentrations of certain molecules reflecting biological selection. Homochirality is a special and powerful example of such biology selection. Environmentally, a depletion of hydrogen in the lower atmosphere may be a sign of metabolism. A discovery of life in liquid methane and ethane would be our first compelling indication that the universe is full of diverse and wondrous life forms. Full article
(This article belongs to the Special Issue The Physico-Chemical Limits of Life)
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682 KiB  
Hypothesis
The Physical, Chemical and Physiological Limits of Life
by Dirk Schulze-Makuch, Alexander Schulze-Makuch and Joop M. Houtkooper
Life 2015, 5(3), 1472-1486; https://doi.org/10.3390/life5031472 - 17 Jul 2015
Cited by 11 | Viewed by 23388
Abstract
Life on Earth displays an incredible diversity in form and function, which allows it to survive not only physical extremes, but also periods of time when it is exposed to non-habitable conditions. Extreme physiological adaptations to bridge non-habitable conditions include various dormant states, [...] Read more.
Life on Earth displays an incredible diversity in form and function, which allows it to survive not only physical extremes, but also periods of time when it is exposed to non-habitable conditions. Extreme physiological adaptations to bridge non-habitable conditions include various dormant states, such as spores or tuns. Here, we advance the hypothesis that if the environmental conditions are different on some other planetary body, a deviating biochemistry would evolve with types of adaptations that would manifest themselves with different physical and chemical limits of life. In this paper, we discuss two specific examples: putative life on a Mars-type planet with a hydrogen peroxide-water solvent and putative life on a Titan-type planetary body with liquid hydrocarbons as a solvent. Both examples would have the result of extending the habitable envelope of life in the universe. Full article
(This article belongs to the Special Issue The Physico-Chemical Limits of Life)
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