"use value" economics in the microcosmos

The Scientist | Microorganisms living in deep sea hydrothermal vents can grow off of energy derived from one of the simplest forms of anaerobic respiration ever described, according to a study published this week in Nature.

The reaction -- in which a chemical called formate is broken down into hydrogen and carbon dioxide -- was previously thought to be too energy poor to support the growth of even the smallest organisms. Finding single-celled microbes from Domain Arcahaea that can glean energy from it may point the way towards efficient hydrogen fuel production while providing clues as to how our planet's earliest inhabitants survived the harsh environment of a young Earth.

Formate is the simplest carboxylate anion, consisting of just one carbon, one hydrogen, and two oxygen atoms, and is an important player in fermentation reactions and anaerobic digestion. Some microbes are known to convert formate to methane and CO2 to produce energy, but the conversion of formate into hydrogen and CO2 wasn't thought to release enough energy to support microbial growth.

The problem, it seemed, was that the accumulation of hydrogen inhibits the reaction from continuing to occur. But in special circumstances, this may not be the case. In 2008, for example, Stams and his colleagues showed that in microbial communities where methanogens -- archaea that produce methane as a byproduct of metabolism -- live in partnership with fermentative bacteria that convert formate to hydrogen and CO2, the methanogens consume the hydrogen product of the reaction, allowing the reaction to continue. In doing so, enough energy is generated to support the growth of the bacteria.

The new study provides the first evidence that a microbe can derive energy from this conversion without the help of any partners. Sung Gyun Kang of the Korea Ocean Research and Development Institute and his colleagues were sequencing the genome of a strain of the deep-sea hydrothermal vent archaea Thermococcus onnurineus when they noticed it contained many copies of formate dehydrogenases and hydrogenases thought to be involved in formate conversion reactions.