Researchers at the University of Nebraska-Lincoln (UNL), with colleagues from North Carolina State University and the University of Connecticut, have engineered the hyperthermophilic anaerobe Thermotoga maritima to produce 46% more hydrogen per cell than the wild type.

The team’s highest reported yield—5.7 units of hydrogen for every unit of glucose fed to the bacterium—easily surpassed the theoretical limit of 4 units proposed in 1977 by researcher Rudolf Thauer. A paper on their work is published in the journal Applied and Environmental Microbiology.

The feat represents a breakthrough in the global effort to scale up the sustainable production of clean-burning hydrogen for vehicles and heavy industry, said Raghuveer Singh, who who conducted the research as part of his dissertation.

The T. maritima bacterium ferments sugar into simpler carbon-based molecules that fuel two processes: growing new cells and producing metabolites—one of which is hydrogen. But under normal conditions, most of that carbon gets funneled into the biological machinery that cranks out new cells, leaving little left over for hydrogen production.

There’s a strong coupling between hydrogen synthesis and the growth of new cells, and this coupling needs to be weakened in order to increase the yield of hydrogen.

—Raghuveer Singh

The researchers decided to inactivate temporarily a gene that has no effect on cell growth but slows hydrogen production in T. maritima. When they did, a second gene—this one involved in transporting sugar—spontaneously mutated to prevent a lethal buildup of sugar-based metabolites. That mutation also dramatically redirected the bacterium’s energy expenditure from cell growth to hydrogen production, creating a new strain that the researchers named Tma 200.

After transferring the newly mutated gene into a naturally occurring version of T. maritima, the researchers found that the bacterium overproduced hydrogen just as Tma 200 did—confirming the influence of sugar uptake on hydrogen yields.

Singh, Blum and colleague Derrick White have since worked with NUtech Ventures to apply for patent protection of the genetic technique, which Singh described as a “promising strategy” for increasing bacterial production of any potential metabolite.

The researchers received support from the US Department of Energy.

Resources

• Raghuveer Singh, Derrick White, Yaşar Demirel, Robert Kelly, Kenneth Noll, and Paul Blum (2018) “Uncoupling Fermentative Synthesis of Molecular Hydrogen from Biomass Formation in Thermotoga maritima” Appl. Environ. Microbiol. doi: 10.1128/AEM.00998-18