Photosynthesis creates the food we eat and the oxygen we breathe - could it also help supply our future energy requirements by creating clean-burning hydrogen?
Photosynthesis creates the food we eat and the oxygen we breathe - could it also help supply our future energy requirements by creating clean-burning hydrogen? Researchers studying the single-celled green alga that produces hydrogen, named Chlamydomonas reinhardtii, have discovered a new fermentation pathway within it, one that was previously unknown and that could open a window to new possibilities for increasing hydrogen production.
Algae, which often inhabit soils, naturally produce small amounts of hydrogen when deprived of oxygen. Similar to yeast and other bacteria, under non-aerial conditions this algae produces the energy it needs through fermentation. During the fermentation, hydrogen is released as a result of the activity of an enzyme called hydrogenase which is activated by electrons originating either from the discharge of organic compounds or from the splitting of water by photosynthesis. Normally, only a small part of these electrons is used to produce hydrogen. However, a main research goal is to develop ways to increase this amount, which will lead to an increase in the amount of hydrogen obtained.
In the new study, published by Alexandra Dubini and her colleagues in the scientific journal Journal of Biological Chemistry, researchers from the Department of Plant Biology at the Carnegie Institution, from the National Renewable Energy Laboratory and the Colorado School of Minerals examined metabolic processes in a genetically modified strain that was unable to produce a hydrogenase enzyme for itself active.
The researchers expected that cell metabolism would compensate for this by increasing other pathways, such as those that produce formate and ethanol as end products. In contrast, the algae activated a different metabolic pathway leading to the creation of the compound succinate, which was not previously linked to any fermentation process in this algae. It is worth noting that succinate, a very common industrial chemical synthesized from petroleum, is included in the US Department of Energy's list of the dozen most important chemicals obtained from biomass.
"We actually did not know that this particular metabolic pathway of fermentation existed in algae until we created the transgenic strain," says one of the researchers. "These findings imply that there is a lot of flexibility between the different pathways in which algae use carbon under non-aerobic conditions. By blocking and changing some of these metabolic pathways, we can increase the contribution of electrons to the enzyme under these conditions and increase the levels of hydrogen obtained."
The researcher points out that it is very likely from an evolutionary point of view that the organisms living in the soil will have a variety of metabolic pathways at their disposal. Oxygen levels, nutrient availability, and levels of metals and toxins in the soil can change drastically, both in the short and long term. "In such a changing environment, such organisms must develop flexible metabolic pathways for themselves; The variety of conditions to which they are exposed may favor one energy pathway over another, which will help the organism cope better, from an evolutionary point of view, with its living conditions," explains the researcher.
The researchers led a joint effort to obtain a complete algal genome sequence, which would allow them to identify key genes that encode the same proteins involved in both fermentation and hydrogen production. The researchers feel that there is an immediate importance in the creation of new transgenic strains that could help us in understanding the acceptance of fermentation pathways and hydrogen production. One of the main researchers explains: "The main goal of this research is to gain a basic understanding of the variety of possibilities for metabolic processes that occur in algae and what their interrelationships are; These efforts will lead to the development of innovative ways to create renewable hydrogen and other biofuels like it, which will contribute to all of us energetically."
"These are really exciting times in this field," says one of the researchers. "The tools developed at the Carnegie Institution and by other groups in the field present unprecedented opportunities for scientists looking for important advances in our understanding of the basic biology of organisms such as the aforementioned algae."
As a possible alternative source of energy to fuels derived from fossils (primarily oil), the use of hydrogen will significantly reduce the emission levels of greenhouse gases. Those who support the production of hydrogen based on algae point out that, unlike ethanol produced from agricultural crops, this method will not compete with the production of food from agricultural land.
