University of Otago microbiologists Prof Greg Cook (left) and PhD candidate Chris Greening examine a culture of hydrogen-oxidising bacteria. Photo by Gerard O'Brien.
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
Helping clarify the role of soil micro-organisms in the
global hydrogen cycle is a finding of wide environmental
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
They also found the bacterium ramps up these enzymes'
activity when starved of oxygen and its usual carbon-based
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
These enzymes promote the formation, or utilisation, of
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
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