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University of Otago researchers have helped solve the great disappearing hydrogen gas mystery.
For the past 30 years, scientists have known that 80% of all hydrogen released into the air is rapidly removed through soil activity, but exactly what was carrying out the recycling has remained unclear.
Otago scientists have now provided a more detailed answer, uncovering microbial soil processes that help ensure that hydrogen - an explosive gas - remains at low levels in the earth's atmosphere.
Helping clarify the role of soil micro-organisms in the global hydrogen cycle is a finding of wide environmental significance.
The scientists, from the Otago microbiology and immunology department, have shown that the soil bacterium Mycobacterium smegmatis uses two special enzymes that can efficiently scavenge hydrogen as fuel at very low concentrations.
They also found the bacterium ramps up these enzymes' activity when starved of oxygen and its usual carbon-based energy sources.
The findings have just been published in prestigious journal Proceedings of the National Academy of Sciences.
And the scientists have also indirectly gained further insights into how the micro-organism responsible for tuberculosis can persist and survive in the human body, even when it cannot grow.
Study lead author and Otago PhD candidate Chris Greening said successfully completing the research had been a ''buzz'', and the environmental significance of hydrogen cycling by bacteria was ''incredibly important''.
Mr Greening is an Oxford University biochemistry graduate who had sought to undertake doctoral research at microbiologist Prof Greg Cook's laboratory in Dunedin after hearing a talk Prof Cook gave at Oxford several years ago.
The latest findings emerged from a project led by Prof Cook, of the Otago microbiology and immunology department, which has been investigating why the mycobacteria family, which includes those that cause Tb and leprosy, have genes encoding hydrogenase enzymes.
These enzymes promote the formation, or utilisation, of gaseous hydrogen.
Prof Cook said hydrogen utilisation was essential in several micro-organisms that were human pathogens, and the significance of hydrogenases in the genome of Mycobacterium tuberculosis had been overlooked.
The question had now been raised about whether the ''extraordinary persistence'' of M. tuberculosis in the human host was related to its ability to survive by scavenging intracellular hydrogen even when oxygen was no longer available.
These enzymes could represent ''an unexplored and unique target for the development of new antimicrobials against tuberculosis'', he said.
The team's project was supported by a Marsden Fund Grant awarded to Prof Cook and study co-author Dr Michael Berney.
The other co-authors include Otago microbiology PhD student Kiel Hards,and Prof Ralf Conrad, director of the Max-Planck Institute for Terrestrial Microbiology in Marburg, Germany.