Arctic bacteria - some like it hot

Surprisingly high numbers of heat-loving bacteria found in the cold Arctic Ocean

In subzero sediments off the island of Spitsbergen, scientists from the German Max Planck Institute for Marine Microbiology have detected high numbers of thermophilic (heat-loving) bacteria that are adapted to live in much warmer habitats. These thermophiles exist in the Arctic as spores - dormant forms that withstand adverse conditions for long periods, waiting for better times. Experimental incubations at 40 to 60 degrees Celsius revive the Arctic spores, which appear to have been transported from distant hot spots. The discovery could shed new light on one of microbiology’s great hypotheses: "Everything is everywhere, but, the environment selects." (Science, September 18, 2009)

Research into temperature adaptations of psychrophilic (cold-loving) bacteria in Spitsbergen’s permanently cold fjords has made a new breakthrough. Biological activity was measured by incubating sediment samples with labelled substrate at increasing temperatures. The scientists were impressed to see the activity increase dramatically above 40 degrees Celsius. Some dormant spores had apparently come back to life.

The results presented a unique opportunity to study misplaced microbes in a quantitative way. Using metabolic rate measurements, the researchers estimated that a single gram of the Arctic sediment contains up to 100 000 thermophilic spores. This abundance combined with the unusual location is what Max Planck Director Prof. Bo Barker Jørgensen finds exciting: "What is novel here is not the discovery of thermophiles in the Arctic, but demonstrating their high numbers and constant rate of supply." By measuring the sediment accumulation rate, the team calculated an annual deposition of 100 million thermophiles per square metre of the seabed.

So, where are the Arctic thermophiles coming from? Lead author Casey Hubert narrows down the possibilities: "The large and steady flux of anaerobic bacteria indicates that they are coming from a huge anoxic (free of oxygen) source." Transport pathways connecting these hot spots to the cold ocean must also exist. The researchers speculate that fluid circulation through spreading ridges where the ocean crust forms and "black smokers" and other hydrothermal vents occur, since bacteria from these systems are genetically similar to the Arctic thermophiles. Another source could be deep hot sub-marine oil reservoirs where gas and oil leak upwards, eventually penetrating the sea floor. "The genetic similarities to bacteria from hot North Sea oil reservoirs are striking," adds Dr. Hubert. The scientists hope further experiments and genetic forensics will reveal the warm source. The spores might provide a unique opportunity to trace seepages from the hot subsurface, possibly pointing towards undiscovered offshore petroleum deposits.

In the meantime, the findings provide fresh insight for understanding marine biodiversity and the "hidden rare biosphere." Obscured by the major bacterial groups in a given environment are countless minorities that do not contribute to element cycling in any detectable way. Microbiologists continue to puzzle over how bacteria spread out to establish the vast microbial diversity that is measured in nature. The thermophilic spores appear to hold important clues about this riddle of biogeography, even as they sit dormant in the cold Arctic sediment, waiting in vain for better times.

This work was supported by the Natural Sciences and Engineering Research Council of Canada, the Max Planck Society, the Austrian Science Fund, and the National Science Foundation (US).

Participating Institutes:

Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, D-28359 Bremen, Germany.

Department of Microbial Ecology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.

Department of Marine Sciences, University of North Carolina, Chapel Hill, North Carolina 27599-3300, USA.

Department of Biological Sciences - Microbiology section, Aarhus University, Ny Munkegade, Building 1535, DK-8000 Aarhus C, Denmark.

Center for Geomicrobiology, Department of Biological Sciences, Aarhus University, Ny Munkegade, Building 1535, DK-8000 Aarhus C, Denmark.