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Meyer NR, Morono Y, Dekas AE. Single-cell analysis reveals an active and heterotrophic microbiome in the Guaymas Basin deep subsurface with significant inorganic carbon fixation by heterotrophs. Appl Environ Microbiol 2024; 90:e0044624. [PMID: 38709099 PMCID: PMC11334695 DOI: 10.1128/aem.00446-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2024] [Accepted: 04/04/2024] [Indexed: 05/07/2024] Open
Abstract
The marine subsurface is a long-term sink of atmospheric carbon dioxide with significant implications for climate on geologic timescales. Subsurface microbial cells can either enhance or reduce carbon sequestration in the subsurface, depending on their metabolic lifestyle. However, the activity of subsurface microbes is rarely measured. Here, we used nanoscale secondary ion mass spectrometry (nanoSIMS) to quantify anabolic activity in 3,203 individual cells from the thermally altered deep subsurface in the Guaymas Basin, Mexico (3-75 m below the seafloor, 0-14°C). We observed that a large majority of cells were active (83%-100%), although the rates of biomass generation were low, suggesting cellular maintenance rather than doubling. Mean single-cell activity decreased with increasing sediment depth and temperature and was most strongly correlated with porewater sulfate concentrations. Intracommunity heterogeneity in microbial activity decreased with increasing sediment depth and age. Using a dual-isotope labeling approach, we determined that all active cells analyzed were heterotrophic, deriving the majority of their cellular carbon from organic sources. However, we also detected inorganic carbon assimilation in these heterotrophic cells, likely via processes such as anaplerosis, and determined that inorganic carbon contributes at least 5% of the total biomass carbon in heterotrophs in this community. Our results demonstrate that the deep marine biosphere at Guaymas Basin is largely active and contributes to subsurface carbon cycling primarily by not only assimilating organic carbon but also fixing inorganic carbon. Heterotrophic assimilation of inorganic carbon may be a small yet significant and widespread underappreciated source of labile carbon in the global subsurface. IMPORTANCE The global subsurface is the largest reservoir of microbial life on the planet yet remains poorly characterized. The activity of life in this realm has implications for long-term elemental cycling, particularly of carbon, as well as how life survives in extreme environments. Here, we recovered cells from the deep subsurface of the Guaymas Basin and investigated the level and distribution of microbial activity, the physicochemical drivers of activity, and the relative significance of organic versus inorganic carbon to subsurface biomass. Using a sensitive single-cell assay, we found that the majority of cells are active, that activity is likely driven by the availability of energy, and that although heterotrophy is the dominant metabolism, both organic and inorganic carbon are used to generate biomass. Using a new approach, we quantified inorganic carbon assimilation by heterotrophs and highlighted the importance of this often-overlooked mode of carbon assimilation in the subsurface and beyond.
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Affiliation(s)
- Nicolette R. Meyer
- Department of Earth System Science, Stanford University, Stanford, California, USA
| | - Yuki Morono
- Kochi Institute for Core Sample Research, Institute for Extra-cutting-edge Science and Technology Avantgarde Research (X-STAR), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Nankoku, Kochi, Japan
| | - Anne E. Dekas
- Department of Earth System Science, Stanford University, Stanford, California, USA
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2
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Nagakura T, Schubert F, Wagner D, Kallmeyer J. Biological Sulfate Reduction in Deep Subseafloor Sediment of Guaymas Basin. Front Microbiol 2022; 13:845250. [PMID: 35308366 PMCID: PMC8927301 DOI: 10.3389/fmicb.2022.845250] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Accepted: 02/01/2022] [Indexed: 11/13/2022] Open
Abstract
Sulfate reduction is the quantitatively most important process to degrade organic matter in anoxic marine sediment and has been studied intensively in a variety of settings. Guaymas Basin, a young marginal ocean basin, offers the unique opportunity to study sulfate reduction in an environment characterized by organic-rich sediment, high sedimentation rates, and high geothermal gradients (100–958°C km−1). We measured sulfate reduction rates (SRR) in samples taken during the International Ocean Discovery Program (IODP) Expedition 385 using incubation experiments with radiolabeled 35SO42− carried out at in situ pressure and temperature. The highest SRR (387 nmol cm−3 d−1) was recorded in near-surface sediments from Site U1548C, which had the steepest geothermal gradient (958°C km−1). At this site, SRR were generally over an order of magnitude higher than at similar depths at other sites (e.g., 387–157 nmol cm−3 d−1 at 1.9 mbsf from Site U1548C vs. 46–1.0 nmol cm−3 d−1 at 2.1 mbsf from Site U1552B). Site U1546D is characterized by a sill intrusion, but it had already reached thermal equilibrium and SRR were in the same range as nearby Site U1545C, which is minimally affected by sills. The wide temperature range observed at each drill site suggests major shifts in microbial community composition with very different temperature optima but awaits confirmation by molecular biological analyses. At the transition between the mesophilic and thermophilic range around 40°C–60°C, sulfate-reducing activity appears to be decreased, particularly in more oligotrophic settings, but shows a slight recovery at higher temperatures.
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Affiliation(s)
- Toshiki Nagakura
- GFZ German Research Centre for Geosciences, Section 3.7 Geomicrobiology, Potsdam, Germany
| | - Florian Schubert
- GFZ German Research Centre for Geosciences, Section 3.7 Geomicrobiology, Potsdam, Germany
| | - Dirk Wagner
- GFZ German Research Centre for Geosciences, Section 3.7 Geomicrobiology, Potsdam, Germany
- Institute of Geosciences, University of Potsdam, Potsdam, Germany
| | - Jens Kallmeyer
- GFZ German Research Centre for Geosciences, Section 3.7 Geomicrobiology, Potsdam, Germany
- *Correspondence: Jens Kallmeyer,
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3
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Beulig F, Schubert F, Adhikari RR, Glombitza C, Heuer VB, Hinrichs KU, Homola KL, Inagaki F, Jørgensen BB, Kallmeyer J, Krause SJE, Morono Y, Sauvage J, Spivack AJ, Treude T. Rapid metabolism fosters microbial survival in the deep, hot subseafloor biosphere. Nat Commun 2022; 13:312. [PMID: 35078973 PMCID: PMC8789916 DOI: 10.1038/s41467-021-27802-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Accepted: 12/10/2021] [Indexed: 11/25/2022] Open
Abstract
A fourth of the global seabed sediment volume is buried at depths where temperatures exceed 80 °C, a previously proposed thermal barrier for life in the subsurface. Here, we demonstrate, utilizing an extensive suite of radiotracer experiments, the prevalence of active methanogenic and sulfate-reducing populations in deeply buried marine sediment from the Nankai Trough subduction zone, heated to extreme temperature (up to ~120 °C). The small microbial community subsisted with high potential cell-specific rates of energy metabolism, which approach the rates of active surface sediments and laboratory cultures. Our discovery is in stark contrast to the extremely low metabolic rates otherwise observed in the deep subseafloor. As cells appear to invest most of their energy to repair thermal cell damage in the hot sediment, they are forced to balance delicately between subsistence near the upper temperature limit for life and a rich supply of substrates and energy from thermally driven reactions of the sedimentary organic matter. In the deep sedimentary biosphere, 80 °C has been proposed as an upper thermal barrier for life. Using a suite of radiotracer experiments, this study reports active methanogenic and sulfate-reducing microbial populations with high cell-specific metabolic rates in deeply buried marine sediments from the Nankai Trough subduction zone, which reach temperatures up to 120 °C.
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4
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Interactions between temperature and energy supply drive microbial communities in hydrothermal sediment. Commun Biol 2021; 4:1006. [PMID: 34433861 PMCID: PMC8387401 DOI: 10.1038/s42003-021-02507-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Accepted: 07/30/2021] [Indexed: 11/23/2022] Open
Abstract
Temperature and bioavailable energy control the distribution of life on Earth, and interact with each other due to the dependency of biological energy requirements on temperature. Here we analyze how temperature-energy interactions structure sediment microbial communities in two hydrothermally active areas of Guaymas Basin. Sites from one area experience advective input of thermogenically produced electron donors by seepage from deeper layers, whereas sites from the other area are diffusion-dominated and electron donor-depleted. In both locations, Archaea dominate at temperatures >45 °C and Bacteria at temperatures <10 °C. Yet, at the phylum level and below, there are clear differences. Hot seep sites have high proportions of typical hydrothermal vent and hot spring taxa. By contrast, high-temperature sites without seepage harbor mainly novel taxa belonging to phyla that are widespread in cold subseafloor sediment. Our results suggest that in hydrothermal sediments temperature determines domain-level dominance, whereas temperature-energy interactions structure microbial communities at the phylum-level and below. Lagostina et al. show that relative abundances of Bacteria and Archaea in sediments of Guaymas Basin, Gulf of California, are controlled by temperature, while energy flux explains microbial community structure at the phylum-level and below. Hot diffusion-dominated and energy-depleted sediments are dominated by taxa with relatives in cold subseafloor sediments, while hot sediments with high energy supply from fluid seepage are dominated by taxa also found at hydrothermal vents and in hot springs.
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Heuer VB, Inagaki F, Morono Y, Kubo Y, Spivack AJ, Viehweger B, Treude T, Beulig F, Schubotz F, Tonai S, Bowden SA, Cramm M, Henkel S, Hirose T, Homola K, Hoshino T, Ijiri A, Imachi H, Kamiya N, Kaneko M, Lagostina L, Manners H, McClelland HL, Metcalfe K, Okutsu N, Pan D, Raudsepp MJ, Sauvage J, Tsang MY, Wang DT, Whitaker E, Yamamoto Y, Yang K, Maeda L, Adhikari RR, Glombitza C, Hamada Y, Kallmeyer J, Wendt J, Wörmer L, Yamada Y, Kinoshita M, Hinrichs KU. Temperature limits to deep subseafloor life in the Nankai Trough subduction zone. Science 2020; 370:1230-1234. [PMID: 33273103 DOI: 10.1126/science.abd7934] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2020] [Accepted: 10/13/2020] [Indexed: 02/06/2023]
Abstract
Microorganisms in marine subsurface sediments substantially contribute to global biomass. Sediments warmer than 40°C account for roughly half the marine sediment volume, but the processes mediated by microbial populations in these hard-to-access environments are poorly understood. We investigated microbial life in up to 1.2-kilometer-deep and up to 120°C hot sediments in the Nankai Trough subduction zone. Above 45°C, concentrations of vegetative cells drop two orders of magnitude and endospores become more than 6000 times more abundant than vegetative cells. Methane is biologically produced and oxidized until sediments reach 80° to 85°C. In 100° to 120°C sediments, isotopic evidence and increased cell concentrations demonstrate the activity of acetate-degrading hyperthermophiles. Above 45°C, populated zones alternate with zones up to 192 meters thick where microbes were undetectable.
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Affiliation(s)
- Verena B Heuer
- Center for Marine Environmental Sciences (MARUM), University of Bremen, Bremen, Germany
| | - Fumio Inagaki
- Research and Development Center for Ocean Drilling Science, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan.,Kochi Institute for Core Sample Research, JAMSTEC, Kochi, Japan
| | - Yuki Morono
- Kochi Institute for Core Sample Research, JAMSTEC, Kochi, Japan
| | - Yusuke Kubo
- Center for Deep Earth Exploration (CDEX), JAMSTEC, Yokohama, Japan
| | - Arthur J Spivack
- Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, USA
| | - Bernhard Viehweger
- Center for Marine Environmental Sciences (MARUM), University of Bremen, Bremen, Germany
| | - Tina Treude
- Department of Earth, Planetary, and Space Sciences, Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles (UCLA), Los Angeles, CA, USA
| | - Felix Beulig
- Center for Geomicrobiology, Department of Bioscience, Aarhus University, Aarhus, Denmark
| | - Florence Schubotz
- Center for Marine Environmental Sciences (MARUM), University of Bremen, Bremen, Germany
| | - Satoshi Tonai
- Faculty of Science and Technology, Kochi University, Kochi, Japan
| | - Stephen A Bowden
- Department of Geology and Petroleum Geology, School of Geosciences, University of Aberdeen, Aberdeen, UK
| | - Margaret Cramm
- Department of Biological Sciences, University of Calgary, Calgary, AB, Canada
| | - Susann Henkel
- Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
| | - Takehiro Hirose
- Kochi Institute for Core Sample Research, JAMSTEC, Kochi, Japan
| | - Kira Homola
- Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, USA
| | | | - Akira Ijiri
- Kochi Institute for Core Sample Research, JAMSTEC, Kochi, Japan
| | - Hiroyuki Imachi
- Institute for Extra-cutting-edge Science and Technology Avantgarde Research, JAMSTEC, Yokosuka, Japan
| | - Nana Kamiya
- Graduate School of Integrated Basic Sciences, Nihon University, Tokyo, Japan
| | - Masanori Kaneko
- Geomicrobiology Research Group, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
| | - Lorenzo Lagostina
- Department of Environmental Systems Science, ETH Zürich, Zürich, Switzerland
| | - Hayley Manners
- School of Geography, Earth and Environmental Sciences, Faculty of Science and Engineering, Plymouth University, Plymouth, UK
| | - Harry-Luke McClelland
- Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, USA
| | - Kyle Metcalfe
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
| | - Natsumi Okutsu
- Atmosphere and Ocean Research Institute, University of Tokyo, Tokyo, Japan
| | - Donald Pan
- Department of Subsurface Geobiological Analysis and Research, JAMSTEC, Yokosuka, Japan
| | - Maija J Raudsepp
- School of Earth Sciences, University of Queensland, St. Lucia, QLD, Australia
| | - Justine Sauvage
- Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, USA
| | - Man-Yin Tsang
- Department of Earth Sciences, University of Toronto, Toronto, ON, Canada
| | - David T Wang
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Emily Whitaker
- Department of Oceanography, Texas A&M University, College Station, TX, USA
| | - Yuzuru Yamamoto
- Department of Mathematical Science and Advanced Technology, JAMSTEC, Yokosuka, Japan
| | - Kiho Yang
- Department of Earth System Sciences, Yonsei University, Seoul, Republic of Korea
| | - Lena Maeda
- Center for Deep Earth Exploration (CDEX), JAMSTEC, Yokohama, Japan
| | - Rishi R Adhikari
- Center for Marine Environmental Sciences (MARUM), University of Bremen, Bremen, Germany
| | - Clemens Glombitza
- Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Zürich, Switzerland
| | - Yohei Hamada
- Kochi Institute for Core Sample Research, JAMSTEC, Kochi, Japan
| | - Jens Kallmeyer
- GFZ German Research Centre for Geosciences, Potsdam, Germany
| | - Jenny Wendt
- Center for Marine Environmental Sciences (MARUM), University of Bremen, Bremen, Germany
| | - Lars Wörmer
- Center for Marine Environmental Sciences (MARUM), University of Bremen, Bremen, Germany
| | - Yasuhiro Yamada
- Research and Development Center for Ocean Drilling Science, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan
| | | | - Kai-Uwe Hinrichs
- Center for Marine Environmental Sciences (MARUM), University of Bremen, Bremen, Germany.
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6
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Abstract
How microbial metabolism is translated into cellular reproduction under energy-limited settings below the seafloor over long timescales is poorly understood. Here, we show that microbial abundance increases an order of magnitude over a 5 million-year-long sequence in anoxic subseafloor clay of the abyssal North Atlantic Ocean. This increase in biomass correlated with an increased number of transcribed protein-encoding genes that included those involved in cytokinesis, demonstrating that active microbial reproduction outpaces cell death in these ancient sediments. Metagenomes, metatranscriptomes, and 16S rRNA gene sequencing all show that the actively reproducing community was dominated by the candidate phylum "Candidatus Atribacteria," which exhibited patterns of gene expression consistent with fermentative, and potentially acetogenic, metabolism. "Ca. Atribacteria" dominated throughout the 8 million-year-old cored sequence, despite the detection limit for gene expression being reached in 5 million-year-old sediments. The subseafloor reproducing "Ca. Atribacteria" also expressed genes encoding a bacterial microcompartment that has potential to assist in secondary fermentation by recycling aldehydes and, thereby, harness additional power to reduce ferredoxin and NAD+ Expression of genes encoding the Rnf complex for generation of chemiosmotic ATP synthesis were also detected from the subseafloor "Ca Atribacteria," as well as the Wood-Ljungdahl pathway that could potentially have an anabolic or catabolic function. The correlation of this metabolism with cytokinesis gene expression and a net increase in biomass over the million-year-old sampled interval indicates that the "Ca Atribacteria" can perform the necessary catabolic and anabolic functions necessary for cellular reproduction, even under energy limitation in millions-of-years-old anoxic sediments.IMPORTANCE The deep subseafloor sedimentary biosphere is one of the largest ecosystems on Earth, where microbes subsist under energy-limited conditions over long timescales. It remains poorly understood how mechanisms of microbial metabolism promote increased fitness in these settings. We discovered that the candidate bacterial phylum "Candidatus Atribacteria" dominated a deep-sea subseafloor ecosystem, where it exhibited increased transcription of genes associated with acetogenic fermentation and reproduction in million-year-old sediment. We attribute its improved fitness after burial in the seabed to its capabilities to derive energy from increasingly oxidized metabolites via a bacterial microcompartment and utilize a potentially reversible Wood-Ljungdahl pathway to help meet anabolic and catabolic requirements for growth. Our findings show that "Ca Atribacteria" can perform all the necessary catabolic and anabolic functions necessary for cellular reproduction, even under energy limitation in anoxic sediments that are millions of years old.
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7
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Mhatre SS, Kaufmann S, Marshall IPG, Obrochta S, Andrèn T, Jørgensen BB, Lomstein BA. Microbial biomass turnover times and clues to cellular protein repair in energy-limited deep Baltic Sea sediments. FEMS Microbiol Ecol 2020; 95:5490327. [PMID: 31095297 DOI: 10.1093/femsec/fiz068] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2018] [Accepted: 05/14/2019] [Indexed: 11/14/2022] Open
Abstract
The discovery of active microbial life deeply buried beneath the seafloor has opened important questions: how do microorganisms cope with extreme energy limitation, what is their metabolic activity, and how do they repair damages to essential biomolecules? We used a D:L-amino acid model to calculate microbial biomass turnover times. We used a metagenome and metatranscriptome analysis to investigate the distribution of the gene that encodes Protein-L-iso aspartate(D-aspartate) O-methyltransferase (PCMT), an enzyme which recognizes damaged L-isoapartyl and D-aspartyl residues in proteins and catalyzes their repair. Sediment was retrieved during the Integrated Ocean Drilling Program (IODP) Expedition 347 from Landsort Deep and the Little Belt in the Baltic Sea. The study covers the period from the Baltic Ice Lake ca. 13 000 years ago to the present. Our results provide new knowledge on microbial biomass turnover times and protein repair in relation to different regimes of organic matter input. For the first time, we show that the PCMT gene was widely distributed and expressed among phylogenetically diverse groups of microorganisms. Our findings suggest that microbial communities are capable of repairing D-amino acids within proteins using energy obtained from the degradation of a mixture of labile compounds in microbial necromass and more recalcitrant organic matter.
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Affiliation(s)
- Snehit S Mhatre
- Center for Geomicrobiology, Department of Bioscience, Aarhus University, Ny Munkegade 114, 8000 Aarhus C, Denmark.,NordCEE, Department of Biology, University of Southern Denmark, Compusvej 55, 5230 Odense M, Denmark
| | - Stefan Kaufmann
- Center for Geomicrobiology, Department of Bioscience, Aarhus University, Ny Munkegade 114, 8000 Aarhus C, Denmark
| | - Ian P G Marshall
- Center for Geomicrobiology, Department of Bioscience, Aarhus University, Ny Munkegade 114, 8000 Aarhus C, Denmark
| | - Stephen Obrochta
- Graduate School of International Resource Sciences, Department of Earth Resource Science, Akita University, 1-1 Tegatagakuen-machi, Akita City 010-8502, Japan
| | - Thomas Andrèn
- School of Natural Sciences, Technology and Environmental Studies, Södertörn University, Alfred Nobels all 7, Flemingsberg, 14189 Huddinge, Sweden
| | - Bo Barker Jørgensen
- Center for Geomicrobiology, Department of Bioscience, Aarhus University, Ny Munkegade 114, 8000 Aarhus C, Denmark
| | - Bente Aa Lomstein
- Center for Geomicrobiology, Department of Bioscience, Aarhus University, Ny Munkegade 114, 8000 Aarhus C, Denmark.,Section for Microbiology, Department of Bioscience, Aarhus University, Ny Munkegade 114, 8000 Aarhus C, Denmark
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8
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Orsi WD, Schink B, Buckel W, Martin WF. Physiological limits to life in anoxic subseafloor sediment. FEMS Microbiol Rev 2020; 44:219-231. [PMID: 32065239 PMCID: PMC7269680 DOI: 10.1093/femsre/fuaa004] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2019] [Accepted: 02/13/2020] [Indexed: 12/21/2022] Open
Abstract
In subseafloor sediment, microbial cell densities exponentially decrease with depth into the fermentation zone. Here, we address the classical question of 'why are cells dying faster than they are growing?' from the standpoint of physiology. The stoichiometries of fermentative ATP production and consumption in the fermentation zone place bounds on the conversion of old cell biomass into new. Most fermentable organic matter in deep subseafloor sediment is amino acids from dead cells because cells are mostly protein by weight. Conversion of carbon from fermented dead cell protein into methanogen protein via hydrogenotrophic and acetoclastic methanogenesis occurs at ratios of ∼200:1 and 100:1, respectively, while fermenters can reach conversion ratios approaching 6:1. Amino acid fermentations become thermodynamically more efficient at lower substrate and product concentrations, but the conversion of carbon from dead cell protein into fermenter protein is low because of the high energetic cost of translation. Low carbon conversion factors within subseafloor anaerobic feeding chains account for exponential declines in cellular biomass in the fermentation zone of anoxic sediments. Our analysis points to the existence of a life-death transition zone in which the last biologically catalyzed life processes are replaced with purely chemical reactions no longer coupled to life.
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Affiliation(s)
- William D Orsi
- Department of Earth and Environmental Sciences, Paleontology and Geobiology, Ludwig-Maximilians-Universität München, 80333 Munich, Germany
- GeoBio-Center, Ludwig-Maximilians-Universität München, 80333 Munich, Germany
| | - Bernhard Schink
- Department of Biology, University of Konstanz, 78457 Constance, Germany
| | - Wolfgang Buckel
- Department of Biology, Philipps-Universität, 35032 Marburg, Germany
| | - William F Martin
- Institute for Molecular Evolution, Heinrich Heine Universität Düsseldorf, 40225 Düsseldorf, Germany
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9
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Liang R, Lau MCY, Baars O, Robb FT, Onstott TC. Aspartic acid racemization constrains long-term viability and longevity of endospores. FEMS Microbiol Ecol 2019; 95:5553460. [DOI: 10.1093/femsec/fiz132] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Accepted: 08/20/2019] [Indexed: 11/12/2022] Open
Abstract
ABSTRACT
Certain microorganisms survive long periods of time as endospores to cope with adverse conditions. Since endospores are metabolically inactive, the extent of aspartic acid (Asp) racemization will increase over time and might kill the spores by preventing their germination. Therefore, understanding the relationship between endospore survivability and Asp racemization is important for constraining the long-term survivability and global dispersion of spore-forming bacteria in nature. Geobacillus stearothermophilus was selected as a model organism to investigate racemization kinetics and survivability of its endospores at 65°C, 75°C and 98°C. This study found that the Asp racemization rates of spores and autoclaved spores were similar at all temperatures. The Asp racemization rate of spores was not significantly different from that of vegetative cells at 65°C. The Asp racemization rate of G. stearothermophilus spores was not significantly different from that of Bacillus subtilis spores at 98°C. The viability of spores and vegetative cells decreased dramatically over time, and the mortality of spores correlated exponentially with the degree of racemization (R2 = 0.9). This latter correlation predicts spore half-lives on the order of hundreds of years for temperatures typical of shallow marine sediments, a result consistent with studies about the survivability of thermophilic spores found in these environments.
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Affiliation(s)
- Renxing Liang
- Department of Geosciences, Princeton University, Princeton, NJ, 08544, USA
| | - Maggie C Y Lau
- Department of Geosciences, Princeton University, Princeton, NJ, 08544, USA
| | - Oliver Baars
- Department of Geosciences, Princeton University, Princeton, NJ, 08544, USA
| | - Frank T Robb
- Department of Microbiology and Immunology, University of Maryland, Baltimore, MD, 21202, USA
| | - Tullis C Onstott
- Department of Geosciences, Princeton University, Princeton, NJ, 08544, USA
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10
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Eickenbusch P, Takai K, Sissman O, Suzuki S, Menzies C, Sakai S, Sansjofre P, Tasumi E, Bernasconi SM, Glombitza C, Jørgensen BB, Morono Y, Lever MA. Origin of Short-Chain Organic Acids in Serpentinite Mud Volcanoes of the Mariana Convergent Margin. Front Microbiol 2019; 10:1729. [PMID: 31404165 PMCID: PMC6677109 DOI: 10.3389/fmicb.2019.01729] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Accepted: 07/12/2019] [Indexed: 11/17/2022] Open
Abstract
Serpentinitic systems are potential habitats for microbial life due to frequently high concentrations of microbial energy substrates, such as hydrogen (H2), methane (CH4), and short-chain organic acids (SCOAs). Yet, many serpentinitic systems are also physiologically challenging environments due to highly alkaline conditions (pH > 10) and elevated temperatures (>80°C). To elucidate the possibility of microbial life in deep serpentinitic crustal environments, International Ocean Discovery Program (IODP) Expedition 366 drilled into the Yinazao, Fantangisña, and Asùt Tesoru serpentinite mud volcanoes on the Mariana Forearc. These mud volcanoes differ in temperature (80, 150, 250°C, respectively) of the underlying subducting slab, and in the porewater pH (11.0, 11.2, 12.5, respectively) of the serpentinite mud. Increases in formate and acetate concentrations across the three mud volcanoes, which are positively correlated with temperature in the subducting slab and coincide with strong increases in H2 concentrations, indicate a serpentinization-related origin. Thermodynamic calculations suggest that formate is produced by equilibrium reactions with dissolved inorganic carbon (DIC) + H2, and that equilibration continues during fluid ascent at temperatures below 80°C. By contrast, the mechanism(s) of acetate production are not clear. Besides formate, acetate, and H2 data, we present concentrations of other SCOAs, methane, carbon monoxide, and sulfate, δ13C-data on bulk carbon pools, and microbial cell counts. Even though calculations indicate a wide range of microbial catabolic reactions to be thermodynamically favorable, concentration profiles of potential energy substrates, and very low cell numbers suggest that microbial life is scarce or absent. We discuss the potential roles of temperature, pH, pressure, and dispersal in limiting the occurrence of microbial life in deep serpentinitic environments.
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Affiliation(s)
- Philip Eickenbusch
- Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Zurich, Switzerland
| | - Ken Takai
- SUGAR Program, Institute for Extra-Cutting-Edge Science and Technology Avant-Garde Research (X-star), Japan Agency for Marine-Earth Science Technology, Yokosuka, Japan
| | | | - Shino Suzuki
- Geomicrobiology Research Group, Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Kochi, Japan
| | - Catriona Menzies
- Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, United Kingdom.,Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen, United Kingdom
| | - Sanae Sakai
- SUGAR Program, Institute for Extra-Cutting-Edge Science and Technology Avant-Garde Research (X-star), Japan Agency for Marine-Earth Science Technology, Yokosuka, Japan
| | - Pierre Sansjofre
- Laboratoire Géosciences Océan UMR 6538, Université de Bretagne Occidentale, Brest, France
| | - Eiji Tasumi
- SUGAR Program, Institute for Extra-Cutting-Edge Science and Technology Avant-Garde Research (X-star), Japan Agency for Marine-Earth Science Technology, Yokosuka, Japan
| | | | - Clemens Glombitza
- Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Zurich, Switzerland.,NASA Ames Research Center, Moffett Field, CA, United States
| | - Bo Barker Jørgensen
- Department of Bioscience, Center for Geomicrobiology, Aarhus University, Aarhus, Denmark
| | - Yuki Morono
- Geomicrobiology Research Group, Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Kochi, Japan
| | - Mark Alexander Lever
- Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Zurich, Switzerland
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Predominance of Anaerobic, Spore-Forming Bacteria in Metabolically Active Microbial Communities from Ancient Siberian Permafrost. Appl Environ Microbiol 2019; 85:AEM.00560-19. [PMID: 31152014 DOI: 10.1128/aem.00560-19] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Accepted: 05/22/2019] [Indexed: 11/20/2022] Open
Abstract
The prevalence of microbial life in permafrost up to several million years (Ma) old has been well documented. However, the long-term survivability, evolution, and metabolic activity of the entombed microbes over this time span remain underexplored. We integrated aspartic acid (Asp) racemization assays with metagenomic sequencing to characterize the microbial activity, phylogenetic diversity, and metabolic functions of indigenous microbial communities across a ∼0.01- to 1.1-Ma chronosequence of continuously frozen permafrost from northeastern Siberia. Although Asp in the older bulk sediments (0.8 to 1.1 Ma) underwent severe racemization relative to that in the youngest sediment (∼0.01 Ma), the much lower d-Asp/l-Asp ratio (0.05 to 0.14) in the separated cells from all samples suggested that indigenous microbial communities were viable and metabolically active in ancient permafrost up to 1.1 Ma. The microbial community in the youngest sediment was the most diverse and was dominated by the phyla Actinobacteria and Proteobacteria In contrast, microbial diversity decreased dramatically in the older sediments, and anaerobic, spore-forming bacteria within Firmicutes became overwhelmingly dominant. In addition to the enrichment of sporulation-related genes, functional genes involved in anaerobic metabolic pathways such as fermentation, sulfate reduction, and methanogenesis were more abundant in the older sediments. Taken together, the predominance of spore-forming bacteria and associated anaerobic metabolism in the older sediments suggest that a subset of the original indigenous microbial community entrapped in the permafrost survived burial over geological time.IMPORTANCE Understanding the long-term survivability and associated metabolic traits of microorganisms in ancient permafrost frozen millions of years ago provides a unique window into the burial and preservation processes experienced in general by subsurface microorganisms in sedimentary deposits because of permafrost's hydrological isolation and exceptional DNA preservation. We employed aspartic acid racemization modeling and metagenomics to determine which microbial communities were metabolically active in the 1.1-Ma permafrost from northeastern Siberia. The simultaneous sequencing of extracellular and intracellular genomic DNA provided insight into the metabolic potential distinguishing extinct from extant microorganisms under frozen conditions over this time interval. This in-depth metagenomic sequencing advances our understanding of the microbial diversity and metabolic functions of extant microbiomes from early Pleistocene permafrost. Therefore, these findings extend our knowledge of the survivability of microbes in permafrost from 33,000 years to 1.1 Ma.
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