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      Power limits for microbial life

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          To better understand the origin, evolution, and extent of life, we seek to determine the minimum flux of energy needed for organisms to remain viable. Despite the difficulties associated with direct measurement of the power limits for life, it is possible to use existing data and models to constrain the minimum flux of energy required to sustain microorganisms. Here, a we apply a bioenergetic model to a well characterized marine sedimentary environment in order to quantify the amount of power organisms use in an ultralow-energy setting. In particular, we show a direct link between power consumption in this environment and the amount of biomass (cells cm -3) found in it. The power supply resulting from the aerobic degradation of particular organic carbon (POC) at IODP Site U1370 in the South Pacific Gyre is between ∼10 -12 and 10 -16 W cm -3. The rates of POC degradation are calculated using a continuum model while Gibbs energies have been computed using geochemical data describing the sediment as a function of depth. Although laboratory-determined values of maintenance power do a poor job of representing the amount of biomass in U1370 sediments, the number of cells per cm -3 can be well-captured using a maintenance power, 190 zW cell -1, two orders of magnitude lower than the lowest value reported in the literature. In addition, we have combined cell counts and calculated power supplies to determine that, on average, the microorganisms at Site U1370 require 50–3500 zW cell -1, with most values under ∼300 zW cell -1. Furthermore, we carried out an analysis of the absolute minimum power requirement for a single cell to remain viable to be on the order of 1 zW cell -1.

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          Each recent report of liquid water existing elsewhere in the Solar System has reverberated through the international press and excited the imagination of humankind. Why? Because in the past few decades we have come to realize that where there is liquid water on Earth, virtually no matter what the physical conditions, there is life. What we previously thought of as insurmountable physical and chemical barriers to life, we now see as yet another niche harbouring 'extremophiles'. This realization, coupled with new data on the survival of microbes in the space environment and modelling of the potential for transfer of life between celestial bodies, suggests that life could be more common than previously thought. Here we examine critically what it means to be an extremophile, and the implications of this for evolution, biotechnology and especially the search for life in the Universe.
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                Author and article information

                Front Microbiol
                Front Microbiol
                Front. Microbiol.
                Frontiers in Microbiology
                Frontiers Media S.A.
                15 July 2015
                : 6
                1Department of Earth Sciences, University of Southern California, Los Angeles CA, USA
                2Department of Biological Sciences, University of Southern California, Los Angeles CA, USA
                Author notes

                Edited by: Mark Alexander Lever, ETH Zürich, Switzerland

                Reviewed by: Arthur J. Spivack, University of Rhode Island, USA; Hans Røy, Aarhus University, Denmark

                *Correspondence: Douglas E. LaRowe, Department of Earth Sciences, University of Southern California, Zumberge Hall of Sciences, 3651 Trousdale Parkway, Los Angeles, CA 90089-0740, USA, larowe@

                This article was submitted to Extreme Microbiology, a section of the journal Frontiers in Microbiology

                Copyright © 2015 LaRowe and Amend.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                Page count
                Figures: 5, Tables: 0, Equations: 9, References: 81, Pages: 11, Words: 0
                Funded by: Center for Dark Energy Biosphere Investigations (C-DEBI)
                Award ID: 274
                Funded by: NASA Astrobiology Institute — Life Underground (NAI-LU)
                Award ID: 048
                Original Research


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