Biological Hydrogen Production

I suspect that there is more tothis story than meets the eye.  However,in the meantime we have confirmation of hydrogen production.  The really good news is that this gives us a naturalway to produce gaseous hydrogen at modest cost and that is surely good news.

The next question is whether thisis a cost effective way to convert solar energy directly into hydrogen.  If that were to work out, the advantage ishuge.  Close to utilization theadvantages of hydrogen are high.  It onlybecomes a problem if we decide to ship it.

Even converting hydrogen intoelectricity is a pretty efficient process in the right circumstances.

This may all stall in thedetails, but at least we now have the option to play with.

Hydrogen Production Comes Naturally to Ocean Microbe

Cyanobacterium gives off hydrogen as by-product of day-to-dayprocesses.

December 14, 2010

By Katharine Sanderson

A seemingly unremarkable ocean microbe turns out to be a multitasker --it can not only photosynthesize, but can also produce large amounts ofhydrogen, opening up a potential way to make the gas cheaply for fuel.

The single-celled cyanobacteriumCyanothece 51142 can make hydrogen inair, Himadri Pakrasi of Washington University in St Louis, Missouri, andhis colleagues report in Nature Communications1. Until now, the only organismsknown to make hydrogen could only produce it in an oxygen-free environment --making it a potentially expensive process to scale-up.

Cyanothece 51142 was discovered in 1993, off the coast of Texas, byLouis Sherman of Purdue University in West Lafayette, Indiana, a co-author onthe study. Pakrasi later discovered that the bacterium has a two-stage dailycycle. During the day it undergoes photosynthesis, using sunlight and carbondioxide to make oxygen and branching chains of glucose molecules calledglycogen. When the Sun goes down, the microbe's nitrogenase enzyme kicks intoaction, using the energy stored in the glycogen to fix nitrogen from the air intoammonia. Hydrogen is formed as a by-product.

The two mechanisms are different in that photosynthesis is an aerobicprocess -- one that requires oxygen -- whereas nitrogen fixation, and,consequently, hydrogen production, can take place only anaerobically, becausecontact with oxygen destroys the nitrogenase enzyme. But Cyanothece 51142manages to fix nitrogen even in the presence of atmospheric oxygen by burningcellular oxygen to produce energy. Because no photosynthesis is taking place,the bacterium uses up its cellular oxygen so that the nitrogenase enzyme iseffectively in a largely oxygen-free environment.

Rhythmic reactions

Cyanothece 51142 has a natural circadian rhythm that allows it to be'trained' to produce even more hydrogen.

After a single 12-hour-day and 12-hour-night cycle, Pakrasi and histeam kept the lights on for a further 48 hours straight. During this time, themicrobes continued with their 'night-time' nitrogen fixation and hydrogenproduction in the period that would normally have been dark, but made more fuelfor the process by photosynthesizing. The researchers found that under theseconditions the microbes adjusted their photosynthetic capacity to maximizenitrogen fixation.

The amount of hydrogen produced in this way -- 150 micro moles permilligram of chlorophyll per hour -- is the most ever recorded in naturalcyanobacteria under normal atmosperic conditions, says Pakrasi. If the bacteriabehaved in the same way in a litre of culture medium as they did in the 25millilitres of medium used in the experiment, they would make just over 900 mlof hydrogen in 48 hours -- the time taken for the experiment.

Natural high

"This is the most effective system published so far for hydrogenproduction," says Oliver Lenz at HumboldtUniversity in Berlin, who works on the enzyme hydrogenase.In his work, Lenz has grafted hydrogenase directly onto photosystem I, aprotein unit needed for photosynthesis. Naturally occurring bacteria can'tcompete with such systems, with hydrogen production rates in Lenz's systemachieving greater volumes -- 3,000 micro mols of hydrogen per milligram ofchlorophyll per hour, Lenz says -- but the system remains untested in a naturalsetting, and that's the advantage of Pakrasi's discovery. "I never expectedsuch high rates for a natural organism," Lenz adds. Synthetic approachessuch as Lenz's suffer from being short lived, Pakrasi says, often running outof steam within hours, whereas the cyanobacteria "just keep going fordays".

Organisms other than cyanobacteria, such as the alga Chlamydomonasreinhardtii, also produce hydrogen at similar rates, says Olaf Kruse of Bielefeld Universityin Germany,who works with the species. But these other microbes need strict anaerobicconditions to work. Kruse is keen to see Pakrasi scale up his experiments tocheck thatCyanothece 51142 works as well when cultured in larger volumes.Pakrasi says that his team is about to begin this work, and has already movedfrom 25 ml of culture to 200 ml with similar results.

At the moment, Cyanothece 51142 has small amounts of a hydrogenase thateats up some of the hydrogen as it is produced. To make Cyanothece 51142 workbetter, Lenz suggests genetically modifying the bacterium to contain a moreefficient hydrogenase enzyme, so less hydrogen is lost.

The work shows what an unmodified cyanobacterium is capable of, saysPakrasi. There are at least 10 other strains of Cyanothece, and Pakrasi expectsthese to work in a similar way. "One can -- and we have -- enhance therate by making genetic modifications to the system," he says.

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