Why do we focus on hydrogen?
With the rising of the world population and the higher average lifespan resulting from the development of science and technology, more energy is required to meet people’s growing demand. However, existing mineral resources on the earth, mainly known as coals, oil and gas, are limited and non-renewable. In order to solve this dilemma, we must find ways to obtain green energy resources with the assistance of modern technology to maintain sustainable development. Hydrogen energy, as a kind of green energy, is an efficient fuel and can be widely used in chemical synthesis, smelting process, etc. As a new energy, hydrogen energy development and utilization is still in its infancy.
How do we obtain hydrogen?
Now several methods are used for the production of hydrogen energy, including water electrolysis, coal gasification, heavy oil and natural gas water vapor catalytic conversion, etc. The relatively green method is water electrolysis, which means hydrogen can be produced by pyrolysis of water with the usage of light-resourced battery. Additionally, we found that there are many photosynthetic bacteria in the biological world with the corresponding nitrogenase and hydrogenase which can use light in the appropriate conditions to produce hydrogen . The main mechanism is that the nitrogenase can turn ATP, protons and electrons into H2, while ATPs come from the photosynthetic phosphorylation, part of the protons are from the tricarboxylic acid cycle, and other parts are from the ATP synthase. The electrons use organic acid (glucose, succinic acid, malic acid) as the donor.
Opportunities and challenges we face
The use of photosynthetic bacteria has a good application prospect. They use organic acids as electron donor to produce hydrogen, and the organic wastewater from such as food factories can be used during this process.
But during the process of light fermentation,there are two major problems we have to face.
First, photoelectric conversion efficiency of photosynthetic bacteria are relatively low. Rhodobacter sphaeroides 2.4.1 use photosynthetic reaction center to absorb electrons and by photoion separation they produce electronics. The photochemical conversion efficiency is only 8.4% at 522 nm and 19% at 860 nm.
Second, a reasonable photobioreactor makes it possible to maximize the use of light energy by photosynthetic bacteria, but actually there's no photobioreactor that could meet the demand of Rhodobacter sphaeroides 2.4.1, which is one of the challenges we face.
What are we doing?
Improve photoelectric conversion efficiency
We used Rhodobacter sphaeroides 2.4.1 as a chassis organism for this study. Rhodobacter sphaeroides 2.4.1, as a type of non-sulfur purple photosynthetic bacteria have their unique absorption spectrum. We hope to broaden its absorption spectrum to enhance its total photon absorption.
Using the principle of fluorescence resonance energy transfer, we fused the fluorescent protein sYFP2 (excitation wavelength 517 nm, emission wavelength 529 nm) to the H subunit of the RC complex of Rhodobacter sphaeroides 2.4.1 in order to enhance the ability of the bulb to absorb photons at 517 nm. At the same time we knocked out crtB to eliminate the effect of carotenoids on photon absorption covered by sYFP2.
The prediction of the RC complex and the sYFP2 distance by protein homology modeling shows that the method is potentially feasible.
To learn more about homology modeling ，please click here.
Design a new type of photobioreactor
Then, we designed a new type of photobioreactor, the idea of which is to combine the light source with the mixing system. We used the latest LED light technology, and gave full play to its merits, including small size, energy saving and environmental protection. With the help of brush on the top and other ancillary equipment, the light source can rotate with the paddles at the same time, which will not affect the flow field and the mixing effect of the photobioreactor.
To learn more about our photobioreactor，please click here.
Blankenship R E, Sayre R T. Comparing photosynthetic and photovoltaic efficiencies and recognizing the potential for improvement.[J]. Science, 2011, 332(6031):805.
Das D, Veziroǧlu T N. Hydrogen production by biological processes: a survey of literature[J]. International Journal of Hydrogen Energy, 2001, 26(1):13-28.
邓文武. 外加电场辅助质子传递供类球红细菌光合产氢研究[D]. 西南大学, 2010.
Miyake J. The science of biohydrogen. Biohydrogen [M]. Manoa: University of Hawaii, 1998.7-18