I wish to suggest constructing the electricity-carbohydrate-hydrogen (ECHo) cycle could meet four basic needs of humans: air, water, food and energy, while minimizing environmental footprints. In it, electricity is a universal high-quality energy carrier; hydrogen is a clear electricity carrier; and carbohydrate is a hydrogen carrier, an electricity storage compound and sources for food, feed and materials. By using this cycle, we could replace crude oil with a new oil -- carbohydrates (CH2O) with highest energy utilization efficiencies, feed the world, power cellular phone, produce plenty of renewable materials and liquid biofuels (e.g., ethanol, butanol, jet fuel), etc. [1].
We conduct our research project based on two platforms: cascade enzyme factories and microbial cell factories (e.g., E. coli and Bacillus subtilis).
Based on cascade enzyme factories, our specific projects include
Sweet hydrogen and sugar fuel cell vehicles. To break the Thauer limit for natural hydrogen-producing microorganisms, we have achieved the production of theoretical yield hydrogen from hexose (i.e., 12 H2 per glucose unit) [2,3]. Via it, we propose the use of sugar as a hydrogen carrier so to solve hydrogen storage challenge. The hypothetical sugar fuel cell vehicles would be the most energy efficiency vehicles. A small fraction of the USA biomass could be sufficient to replace all gasoline [4].
High-power and high-energy density enzymatic fuel cells (i.e., bioinspired sugar battery) [5,6]. To increase fuel utilization efficiency, we have designed the pathways that can produce 24 electrons per glucose for the first time.
Artificial photosynthesis for CO2 utilization [7]. To surpass natural limits of plant photosynthesis, we propose a new system by integrating solar cell, water electrolysis, and CO2 fixation with 20-50 higher energy utilization efficiency and 500-1000 fold higher water conservation, compared to plant photosynthesis.
Enzymatic synthesis of renewable materials. For the first time we are able to convert beta-1,4-glucoisidic bond linked cellulose to alpha-1,-4-bond linked starch as humans dreamed long before. As a result, feeding the world would be not a big problem in the future.
By utilizing microbial cell factories, our specific projects include
Cellulase engineering, metabolic engineering, and consolidated bioprocessing Bacillus subtilis. We have developed a novel enzyme screening platform based on solid cellulosic materials [6] and created the first really recombinant cellulolytic microorganisms that can grow on solid cellulosic materials based on its recombinant cellulases without help of other soluble nutrients [8].
Enzyme engineering by rational design and directed evolution. We are developing redox enzymes that can work on low-cost biomimetic cofactors, which may be the last obstacle to cascade enzyme factories.
Low-cost recombinant protein production and purification as building blocks and synthetic metabolons for cascade enzyme factories and microbial cell factories .
Also, we are investigating the complicated relationship among heterologous cellulose, cellulases, cellulosomes and cellulolytic microorganisms. For example, we find out that increasing substrate accessibility is more important than removing lignin for biomass pretreatment [10]. Displaying minicellulosomes on the surface of microorganisms can expedite microbial cellulose conversion rate by several folds [11].
[1] Zhang Y-HP*, Huang WD. 2012. Constructing the electricity-carbohydrate-hydrogen cycle for sustainability revolution. Trends in Biotechnology, 30: 301-306 (PDF) (opinion).
[2] Zhang Y-HP*, Evans BR, Mielenz JR, Hopkins RC, Adams MWW. 2007. High-yield hydrogen production from starch and water by synthetic enzymatic pathway. PLoS ONE 2(5): e456.
[3] Ye X, Wang Y, Hopkins RC, Adams MWW, Evans BR, Mielenz JR, Zhang Y-HP*. 2009. Spontaneous high-yield production of hydrogen from cellulosic materials and water catalyzed by enzyme cocktails. ChemSusChem 2: 149-152.
[4] Huang WD, Zhang Y-HP*. 2011. Energy efficiency analysis: biomass-to-wheel efficiency related with biofuels production, fuel distribution, and powertrain systems. PLoS One 6(7): e22113 (Analysis).
[5] Zhu ZG, Wang YR, Minteer SD, Zhang Y-HP. 2011. Maltodextrin-powered enzymatic fuel cell through a non-natural enzymatic pathway. Journal of Power Sources 196:7505-7509.
[6] Zhu ZG, Sun FF, Zhang XZ, Zhang Y-HP*. 2012. Deep oxidation of glucose in enzymatic fuel cells through a non-natural synthetic enzymatic pathway containing a cascade of two thermostable dehydrogenases. Biosensors and Bioelectronics 36: 110-115 ( PDF).
[7] Zhang Y-HP*, Chun Y, Chen HG, Feng RL. 2012. Surpassing photosynthesis: high-efficiency and scalable CO2 utilization through artificial photosynthesis. ACS Symposium Series 1097: 275-292 (PDF) (Recent Advances in Post-Combustion CO2 Capture Chemistry), Oxford University Press, UK.
[8] Zhang X-Z, Zhang Y-HP*. 2011. Simple, fast and high-efficiency transformation system for directed evolution of cellulase in Bacillus subtilis. Microbial Biotechnology 4: 98-105 (Highlighted).
[9] Zhang XZ, Zhu ZG, Sathitsuksanoh N, Zhang Y-HP*. 2011. One-step production of lactate from cellulose as sole carbon source without any other organic nutrient by recombinant cellulolytic Bacillus subtilis. Metabolic Engineering 13:364-372.
[10] Rollin J, Zhu ZG, Sathisuksanoh N, Zhang Y-HP*. 2011. Increasing substrate accessibility is more important than removing lignin: A comparison of cellulose solvent-based lignocellulose fractionation and soaking in aqueous ammonia.Biotechnology and Bioengineering 108: 22-30
[11] You C, Zhang X-Z , Sathitsuksanoh N , Lynd LR, Zhang Y-HP*. 2012. Enhanced microbial cellulose utilization of recalcitrant cellulose by an ex vivo cellulosome-microbe complex. Applied and Environmental Microbiology 78(5):1437-1444.
Funding Sources
Federal sources: NSF, DOE BESC, DOE ARPA-E, AFOSR, Army, USDA, Sun Grant
Companies: Shell, DuPont, Equation Group, Taiwan ITRI, Gate Fuels
Foundations: ACS PRF, ORAU