Hydrogen has long been one of the dream energy sources of green and alternative energy programs. A clean fuel source with no negative byproducts and that has complete conversion to heat and energy. It has stood up on the pedestal along with the likes of fusion reactors and other high efficiency technologies. The main difference between it and them being that hydrogen as a fuel source and technology currently exists, while the others are years, if not decades off.

However, reality has shown that even if it exists, obtaining and utilizing it has made its actual usage almost non-existent. The main ways of obtaining a viable quantity of hydrogen fuel has been to extract it from environmental sources, methods that have invariably resulted in environmental damage. Other direct methods of production, such as electrolysis that involves splitting hydrogen atoms from water has a low production rate for the energy cost required to run the process. Steam-methane reforming is another option that produces far more hydrogen directly, but also produces greenhouse gas byproducts, lowering it on the list of viable alternative fuel sources.

The one other source that has been investigated and shown significant progress as more research has been conducted is biological production, otherwise known as biohydrogen. Pure hydrogen or in a form like hydrogen gas is a byproduct for several species or can be induced to become one through some biotechnology involvement. The primary scientific focus has been on bacteria, especially Escherichia coli and its tendency to take on desired production genes easily.

This process, though, is not entirely straightforward, as producing hydrogen as a bacterial byproduct still requires a number of other chemical steps and reactions, all of which the chosen bacteria has to be made to undergo itself. Anaerobic fermentation in order to create hydrogen especially requires a series of steps, but even back in 2008, these requirements were well understood. Thus, progress in this field has been ongoing and increasingly successful.[1]

For anaerobic production, one of the elemental methods to produce hydrogen is to start with glucose and produce formate through the production chain, which can then be converted into free hydrogen. Wild-type E. coli were found to construct 9.8 micromoles of hydrogen per milligram of dry cell weight processed on average. After two genes were separately modified to increase formate transportation and transcription speed, named focA and narL respectively, in two different lines, hydrogen production was found to be increased by around 50%. The first modified gene line, ZF1, produced 14.9 micromoles of hydrogen and the second, ZF3, produced 14.4 micromoles of hydrogen. It was also discovered that the global transcription gene narL was able to synergistically work with the other gene to cause an even higher combined hydrogen production result.[2]

Such a fermentation process has become more and more desired due to applications in almost every possible energy source, whether alternative, renewable, or even classical systems. This production method via bacteria trumps all other hydrogen production methods handily due to the few inputs required other than nutrition for the bacteria and, in return, receiving pure hydrogen ions or hydrogen gas.[3]

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As an aside, a study in December of 2010 presented a constructed artificial neural network (ANN) to estimate and analyze the likely results from a fermentation and hydrogen production process. The accuracy of its results approached 100% and opened up the possibility of using the network to predict other hydrogen production systems and their viability and efficiency as a method.[4]

This includes using cyanobacteria and the process of photosynthesis to produce hydrogen from sunlight. Acting as essentially highly efficient solar panels, these bacteria would create hydrogen by using mutated hydrogenase enzymes that would allow the storage of hydrogen gas directly without allowing its normal reaction with oxygen in the cell to form water. These methods would allow the possibility of free-floating solar collectors of bacteria in places where solar panels could not be constructed. For now, the efficiency is still lower than desired, so more work needs to be done, but cyanobacteria remain a viable biohydrogen production method.[5]

Another source of photosynthesizing unicellular organisms are microalgae, similar to cyanobacteria, but in a completely different part of the tree of life due to them often being eukaryotes rather than bacteria. Thanks to their more advanced biology, microalgae are able to use two separate systems depending on the availability of light. In a sunny environment, photosynthesis would be used as usual, but when light is diminished, the microalgae switch over to using hydrogenase enzymes to catalyze hydrogen gas via different energy pathways. This makes them versatile and able to continue to provide hydrogen energy in a changing environment without being too reliant on one system of production.[6]

Modeling systems have been utilized to determine what the optimum amount of biomass is for microalgae to produce hydrogen without overwhelming the structure and reducing efficiency. Evidence seems to suggest that the size of the biomass will be limited regardless of the medium used and the available nutrients. The model also, however, allows testing of different modified microalgae variants and how changes from the wild type can affect allowed biomass and overall manufacture.[7]

In addition to the creation of engineered bacteria as a whole for forming hydrogen, the construction of large amounts of catalytic enzymes to help in hydrogen formation can assist in rapidly creating more types of bacteria that produce hydrogen by uptaking the enzymes. The manufacture of these enzymes themselves can also be biologically directed thanks to the field of biodesign. Bacteria, E. coli in this case, are co-opted to synthesize the enzymes and form a protein coat around the completed structures in a process called encapsulation that protects the finished enzyme from outside damage. In a short amount of time, a large amount of catalytic enzymes for hydrogen production or, indeed, any other sort of desired chemical formation can be made and boxed up for use elsewhere.[8]

The specifics of this method involves using iron hydrogenase, sometimes nickel-iron hydrogenase, Common in most bacteria, the main limiting factor for proper exploitation of this pathway is the lack of understanding on how to stabilize hydrogen production from it without harming the cell cultures being used. More research will need to be done before this method is chosen over other options, though there is a significant possibility that hydrogen formation through an iron pathway will be more efficient and require less time overall thanks to the enzyme activity.[9]

Due to the ubiquitous availability of hydrogen throughout the processes of life, several avenues of hydrogen acquisition are open to scientists to pursue, all of which may eventually be used in production of hydrogen as an alternative fuel source. The variety of methods and environments that biohydrogen may be fabricated in entails a wide source of free energy in the near future. It is possible that biohydrogen creation may outstrip other forms of alternative and green energy as a primary fuel source for the world’s industries. Either way, exploration into biohydrogen is a broad avenue of potential that will undoubtedly be involved in shaping the future world we all will live in.

References

Liu X, Ren N, Song F, Yang C, Wang A. 2008. Recent advances in fermentative biohydrogen production. Progress in Natural Science [accessed 2016 May 30]; 18:253–258. http://www.sciencedirect.com/science/article/pii/S1002007107000536 Fan Z, Yuan L, Chatterjee R. 2009. Increased Hydrogen Production by Genetic Engineering of Escherichia coli. PLOS One [accessed 2016 May 30]; http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0004432 Rosales-Colunga LM, Rodríguez AL. 2015. Escherichia coli and its application to biohydrogen production. Reviews in Environmental Science and Bio/Technology [accessed 2016 May 30]; 14:123–135. http://link.springer.com/article/10.1007/s11157-014-9354-2 Rosales-Colunga LM, Garcia RG, Rodríguez AL. 2010. Estimation of hydrogen production in genetically modified E. coli fermentations using an artificial neural network. International Journal of Hydrogen Energy [accessed 2016 May 30]; 35:13186–13192. http://www.sciencedirect.com/science/article/pii/S0360319910017763 Masukawa H, Kitashima M, Inoue K, Sakurai H, Hausinger RP. 2012. Genetic engineering of cyanobacteria to enhance biohydrogen production from sunlight and water. AMBIO [accessed 2016 May 30]; 41:169–173. http://www.ncbi.nlm.nih.gov/pubmed/22434447 Dubini A, Ghirardi ML. 2015. Engineering photosynthetic organisms for the production of biohydrogen. Photosynthesis Research [accessed 2016 May 30]; 123:241–253. http://link.springer.com/article/10.1007/s11120-014-9991-x Vargas JV, Kava V, Balmant W, Mariano AB, Ordonez JC. 2016. Modeling microalgae derived hydrogen production enhancement via genetic modification. International Journal of Hydrogen Energy [accessed 2016 May 30]; 51:8101–8110. http://www.sciencedirect.com/science/article/pii/S0360319916308801 Jordan PC, Patterson DP, Saboda KN, Edwards EJ, Miettinen HM, Basu G, Thielges MC, Douglas T. 2013. Self-assembling biomolecular catalysts for hydrogen production. Nature Chemistry [accessed 2016 May 30]; 8:179–185. http://www.nature.com/nchem/journal/v8/n2/full/nchem.2416.html Hei J, Wu C. 2015. [FeFe]-Hydrogenase: Catalytic Center and Modification by Genetic Engineering. Advances in Applied Biotechnology [accessed 2016 May 30]; 333:621–628. http://link.springer.com/chapter/10.1007/978-3-662-46318-5_64

Written by: Sterling Ericsson

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Photo CC: E. coli Bacteria by NIAID https://www.flickr.com/photos/niaid/16578744517