Hydrogen is a potential clean energy storage material. However, it's not truly environmentally friendly unless it is produced from renewable sources.
Ranjini Chatterjee and coworkers, at the University of Kentucky and Farasis Energy (California), have genetically engineered bacteria to produce enhanced levels of hydrogen under oxygen-deprived (fermenting) conditions. This is a step towards creating an autonomous, continual, and renewable hydrogen source.
Genetic engineering.
Escherichia coli (E. coli) bacteria produce hydrogen under oxygen-deprived conditions. The hydrogen molecules are typically used to generate electrons and positively charged hydrogen atoms (protons), which among other uses are important in energy production.
The scientists wanted to rejigger the genetic code of the bacteria to enhance the level of hydrogen molecule production (without converting them to something else), with the goal of capturing the hydrogen produced. They based their experiments on detailed knowledge of relevant metabolic pathways (energy production and consumption pathways) in E. coli bacteria.
The scientists inactivated four genes in E. coli bacteria. The purpose was to increase the concentrations of pyruvate and formate molecules in the bacteria, reduce the metabolic utilization of hydrogen molecules, and to scale back the repression of genes involved in the synthesis of the enzymes pyruvate formate lyase and formate hydrogen lyase (all steps taken to increase hydrogen production by the bacteria).
Enhanced hydrogen yields.
How did this affect hydrogen production and oxygen-deprived growth rate? The scientists found that two of their bacterial strains exhibited a 46% enhanced level of hydrogen production relative to unmodified bacterial cells (the highest rate of hydrogen production was between 4 and 7 hours after the initial cultivation).
These two bacterial strains also grew at a similar rate as unmodified bacteria. This and other metabolic analyses suggest that bacterial function was not disrupted by the genetic engineering.
Evaluation and future directions.
These initial results demonstrate how to switch off particular genes to enhance hydrogen production by E. coli bacteria, without disrupting their ability to grow. Immediate efforts will likely focus on enhancing the level of hydrogen production even further.
Further investigations along these general lines may enable scientists to utilize gut-dwelling microbes, that use molecules other than glucose as their energy source, for hydrogen production. Another longer-term goal may also be to produce other useful molecules derived from pyruvate, simultaneous with the hydrogen production reported here, to further enhance the value and utility of these genetically modified bacteria.
for more information:
Fan, Z.; Yuan, L.; Chatterjee, R.
Increased hydrogen production by genetic engineering of
Escherichia coli.
PLoS ONE 2009, 4, e4432.