Center for Geomicrobiology
at the University of Aarhus

A joint initiative between the Danish National Research Foundation,
the German Max Planck Society, and the University of Aarhus

The Center for Geomicrobiology is a co-operation between the Danish National Research Foundation (DNRF), the German Max Planck Society (MPS), and the University of Aarhus. The MPS and the DNRF will share the financing of the center budget. The University of Aarhus (AU) will fund initial equipment needed for the center and will provide laboratory and office space. The head of the center will be Prof. Bo Barker Jørgensen. He is currently a director of the Max Planck Institute for Marine Microbiology in Bremen and Head of its Department for Biogeochemistry. He will remain a director of the institute in Bremen while leading the Center. The Center will start on October 1st, 2007, and is planned for five years.

It is a new initiative within the MPS to co-fund such a European center outside of Germany and it shows the high priority that the society gives this center plan and the future co-operation with Danish basic research. The proposed center is based on the establishment and hiring of a new research group, rather than growing out of an existing group. BBJ will bring the experience and support of the Max Planck Institute in Bremen, including collaborations with scientists of the MPI. The center will be integrated into the Section for Microbiology at the Department of Biological Sciences and members of this internationally outstanding group will be partners in the Center. The Center also plans co-operation with the Department of Geology at the University of Aarhus and has as a goal to establish a new interdisciplinary research field between biology and geology at the Faculty of Natural Sciences.

Summary
The overall research aim of the Center for Geomicrobiology is to understand how prokaryotic microorganisms drive processes in the subsurface seabed and control the coupling of essential element cycles that ultimately affect ocean chemistry and global climate. Specifically, the Center will develop and adapt methods to detect the activity of subsurface microbial populations in order to explore the diversity and function of the marine “deep biosphere” and how it differs from the much more active surface biosphere.

Deeply buried sediments constitute the largest ecosystem on Earth in terms of volume and organic carbon pool and they harbor the majority of all prokaryotic organisms (bacteria and archaea) on Earth. Yet, they constitute an almost unexplored part of the global environment. Recent developments in analytical and isotope techniques, DNA/RNA-based methods, and drilling and sampling technology have now made this fascinating component of planet Earth available to modern research. Through a targeted sampling of sediments ranging from the surface of the seafloor to hundreds of meters subsurface, and from the present to the many-million-year old geological past, the changes in availability of organic carbon and energy for microbial processes will be studied. A major research goal is to understand how microbial life under extreme energy limitation may thrive in spite of near-zero growth with calculated mean generation times that may reach thousands of years. The potential role of natural radioisotopes to provide energy source for this sub-surface life through the radiolysis of water will be explored.

The research will comprise the development of new and more sensitive methods and the application of these on marine sediments, partly obtained from the Integrated Ocean Drilling Program, IODP. Microbiological and geochemical processes will be analyzed by a) experiments using radioactive or stable isotope tracers, b) reaction-transport modeling of geochemical data, and c) stable isotope analyses indicating past activities. The identity and abundance of selected microbial populations will be analyzed by sequencing and quantification of 16S rRNA genes and of functional genes in extracted DNA. The activity of microbial populations will be characterized from their gene expression by quantification of mRNA of key genes. Key organisms will be enriched and isolated and their physiology studied in laboratory culture in order to interpret the DNA/RNA based information. As a novel approach, the phylogenetic identity and metabolic activity of individual prokaryotic cells will be analyzed experimentally by combined pulse-chase tracer experiments and hybridization probes using the new generation of Secondary Ion Mass Spectrometry (nano-SIMS) for single-cell analyses.

A critical aspect of the planned research is the access to deep and microbiologically uncontaminated sediment cores. This will be obtained through participation in the IODP program as land-based and, when possible, on-board scientists. Deep Biosphere research is one of the three main focus areas of the IODP for the coming decade. The Center for Geomicrobiology will be the first to specifically focus on the integration of marine microbial ecology and deep biosphere research and may thus establish a Danish research consortium at the international forefront of this field.

Bo Barker Jørgensen was co-chief on the first ODP drilling expedition devoted to deep biosphere research in 2002 and is currently a co-proponent of three IODP proposals that all include deep biosphere research, including the South Pacific gyre, the Central American margin, and the anoxic Black Sea. He was recently invited by the president of the IODP to be the first international speaker on the Deep Biosphere as part of the new “IODP Distinguished Researchers and International Leadership Lecture Series”.

The first scientific initiative of the center will be the organization of an international workshop on “Microbial Life under Extreme Energy Limitation”, which addresses the greatest challenge for our understanding of life in the deep subsurface. The workshop is co-chaired by Tori Hoehler from NASA Ames Research Center and Bo Barker Jørgensen together with a local organizing committee from the Section for Microbiology. It will take place at the University of Aarhus, 21-24 October 2007. It is co-sponsored by the International Society for Microbial Ecology, the Federation of European Microbiological Societies, and the new Center for Geomicrobiology. This workshop will bring together internationally leading microbiologists and biogeochemists to present new data and discuss key problems related to the workshop theme (http://bio.au.dk/microenergy)

Scientific background

The discovery of microorganisms in several million year old sedimentary deposits, and even in basement rock, has profoundly changed our perspective on the limits of living organisms. It is now apparent that processes in the geosphere may provide a driving force for life and that, vice versa, the subsurface biosphere has a large impact on geological processes. The slow biological degradation of organic carbon in the deep subsurface and the formation of great quantities of methane have a large-scale impact on sea floor processes, such as the accumulation of gas hydrates, the charging of mud volcanoes, or the formation of carbonate platforms.

With increasing depth and age of marine sediments, microbial cells become increasingly energy limited. At several hundred meters below the sea floor population sizes are still large, yet the energy flux and the theoretical growth rate of the bacteria are orders of magnitude below anything we can understand from research on cultivated microorganisms. This is one of the most intriguing problems in environmental microbiology today. How is it possible to maintain complex functions in prokaryotic cells at an energy flux that barely allows cell growth over many years? Do these organisms have properties beyond our current understanding of microbial life, or are energy sources available that have not yet been identified? Are the deeply buried communities just relicts of a time when the sediment was originally deposited or do they respond to the modern sedimentary environment? Is there a globally unique microbial biosphere deeply buried in the seabed or do the organisms exchange genes with the surface world?

The first research cruise of the international Ocean Drilling Program (ODP) that was devoted to the study of the deep sub-seafloor biosphere took place in 2002. The large amount of new information obtained provided compelling evidence for the nature of this elusive microbial world and triggered a great interest in its further exploration. The current database on prokaryotic cells in deep sediment cores indicates that the deep biosphere may comprise 10-30% of all living biomass and more than half of all microorganisms on Earth. The population densities, 10 000 to 10 000 000 cells per ml down to >750 m sediment depth, vastly exceed those found in ocean water where nearly the entire marine carbon cycle takes place. The sub-seafloor communities thus comprise a “starving majority” among the prokaryotes on Earth.

Sustained supply of energy is a fundamental requirement for life, yet the quantitative constraints on the “energetic habitability” of ecosystems, or planets, are unknown. Understanding the minimum energy requirements for growth and survival may offer a means of interpreting the distribution, composition, and activity of deeply buried communities. The search for alternative, cryptic energy sources has focused on molecular hydrogen. H2 is generated by chemical alterations in young basaltic crust along the mid-oceanic ridges. Yet, most of the seabed lies on old crack-permeable crust in which the potential oxidants for H2, e.g. oxygen or nitrate, appear to persist long enough to exclude that crustal H2 could supply significant reducing power. Interestingly, energy released from the decay of natural radio-nuclides of potassium, thorium or uranium (40K, 232Th, 238U) everywhere in the seabed dissociates water molecules into free radicals and molecules such as H2. This nuclear energy is therefore not only destructive to microbial cells but may also support their metabolic activity. Estimates of the rate of hydrogen generation in sedimentary basins, ca 10-12 M H2 d-1, are comparable to the rates of potential H2 consumption by some of the deep microbial communities in the Pacific seabed. Thus, water radiolysis may significantly contribute to microbial energy consumption in those deep-sea sediments that are most depleted in organic matter.

This potential energy source is particularly interesting in that it is independent of biomass production by photosynthesis. It does not even require an external oxidant. Concurrently with H2, water radiolysis produces oxidants such as O2 which may be directly used for the energy generating re-oxidation of H2. No chemical trace might be left other than the sustained energy metabolism of prokaryotic life. Such a low-energy subsurface biosphere driven by radioactivity would be different from other ecosystems on Earth as it might proceed on a planet without surface life supported by solar energy. It could thus equally well proceed at several km subsurface on Mars. The first evidence of deep terrestrial communities driven by nuclear energy has recently been provided by studies of ambient rocks surrounding 2-3 km deep South African goldmines.

Head of Center: Prof. Bo Barker Jørgensen

Max Planck Institute for Marine Microbiology
Celsiusstr. 1, D-28359 Bremen, Germany
Phone: +49-421-2028-600/-602
Fax: +49-421-2028-690
bjoergenmpi-bremen.de