Cyanothece's clock is set by the environmental cue of changing light levels. But once entrained by the day/night cycle, the clock continues to run even in the absence of the cues. Just as a prisoner kept in solitary confinement will maintain a roughly 24-hour sleep/wake cycle, Cyanothece will continue to fix nitrogen even if it is incubated under continuous light.
As Pakrasi puts it, the entrained microbes are still experiencing "subjective dark" for 12 hours of the day.
More strangely, entrained Cyanothece incubated under continuous light evolve more hydrogen than those cycling between light and dark. This is probably because the energy in light somehow fuels the energy-intensive nitrogenase reaction, says Anindita Bandyopadhyay, PhD, a postdoctoral fellow in Pakrasi's lab. The scientists are still trying to understand exactly why this happens.
In addition to keeping the microbes awake all night, the scientists have another trick up their lab coat sleeves. Cyanothece can survive on the starvation diet of sunlight and air but adaptable microbe that it is, it can also live on carbon-containing molecules or on a mix of sunlight and carbon-containing molecules.
The scientists found that the microbes produced more hydrogen if they were grown in cultures that contained glycerol, a colorless, sweet-tasting molecule that is frequently used as a food additive.
The additional carbon in the glycerol revs up the nitrogenase to meet the increased demand for nitrogen in the cells, Pakrasi says. And the more active the nitrogenase, the more hydrogen is produced.
Despite journalistic hype, Pakrasi warns, hydrogen is not the fuel of tomorrow. It's hard to transport and its energy density is too low. The fuel tank for a semi-trailer powered by hydrogen would take up half
|Contact: Diana Lutz|
Washington University in St. Louis