Scientists Discover How Hydrogen-Making Bacteria Thrive with Cyanide

Bacteria may hold answer for making inexpensive hydrogen.

Published: 15-Feb-2003

A University of Arizona chemist and colleagues from Munich, Germany, have discovered how microbes avoid being poisoned by the cyanide and carbon monoxide compounds they make and incorporate into enzymes. The bacteria use the enzymes to turn water into hydrogen for energy.

Bacteria with this remarkable ability have long been widely dismissed as one of Mother Nature's interesting, if largely useless and unimportant, oddities, said UA chemistry professor Richard S. Glass.

But they now interest industry searching for cheap hydrogen sources for such things as hydrogen-fueled cars and other technologies that fall under President Bush's proposed $1.2 billion hydrogen research program. It may be possible to mimic the microbes' use of iron or other cheap metal in making hydrogen, rather than expensive platinum currently used, Glass said. The petroleum industry, which uses hydrogen to remove sulfur for cleaner-burning fuels, also seeks cheaper sources of hydrogen, he added.

Glass became intrigued with the bacteria while working with microbiologists and biochemists in Munich during his 1999-2000 sabbatical. The bacteria assemble "hydrogenases," or enzymes that catalyze the reactions that produce molecular hydrogen from water. These enzymes consist of two atoms of iron, or else an atom of iron and an atom of nickel, with a group of carbon monoxide molecules and two groups of cyanide molecules attached to the iron.

The team modeled and experimentally validated how bacteria biochemically assemble these toxic hydrogenases. As well as using chemical tests, the scientists verified their findings using mass spectrometry techniques that won scientists the 2002 Nobel Prize in chemistry.

The team is publishing the research in today's issue of Science (Feb. 14), in the article, "Taming of a Poison: Biosynthesis of the NiFe-Hydrogenase Cyanide Ligands." Authors of the research paper are Stefanie Reissmann of the University of Munich, Elisabeth Hochleitner of the Max-Planck Institute for Biochemistry, Hoafan Wang of the University of Arizona, Athanasios Paschos of the University of Munich, Friedrich Lottspeich of the Max-Planck Institute for Biochemistry, Glass, and August Boeck of the University of Munich.

They determined that the bacteria make the toxic "ligands," or little groups of molecules attached to the iron, from a non-toxic, one-carbon protein previously known to be used in the biosynthesis of an amino acid. When activated, this precursor transfers a small unit to a large protein where it is safely manipulated to cyanide.

They discovered that cyanide attached to sulfur before it attaches to iron as the hydrogenases are assembled, "so you never have free cyanide floating around, killing everything off," Glass said. Cyanide rarely attaches to sulfur in nature, he added, but it does in this case.

Understanding how living organisms can thrive by biosynthesizing lethal compounds is relevant for astrobiology, too, Glass speculates.

The one-celled organisms that first appeared on Earth had to face "one tough neighborhood, which included cyanide and other poisons," he noted. "How did they cope?"

Lori Stiles

Friday, 14 February 2003 |
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Richard S. Glass

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