Researchers at the Henry Samueli School of Engineering and Applied Science at UCLA, Los Angeles, have discovered for the first time a way to use proteins as a potential raw material for bio-mass production. Currently, only two types of raw materials, carbohydrates and lipids, are used to produce biofuel and other bio-based chemicals.
"Proteins had been completely ignored as a potential biomaterial because they've been thought of mainly as food. But in fact, there are a lot of different proteins that cannot be used as food," says James C. Liao, the Chancellor's Professor of Chemical and Biomolecular Engineering. "These proteins were overlooked as a resource for fuel or for chemicals because people did not know how to utilize them or how to grow them. We've solved these problems."
"This research is the first attempt to utilize protein as a carbon source for energy production and biorefining," adds Kwang Myung Cho, a UCLA Engineering research scientist. "To utilize protein as a carbon source, complex cellular regulation in nitrogen metabolism had to be rewired. This study clearly showed how to engineer microbial cells to control their cellular nitrogen metabolism."
The process Liao's team developed uses an artificial metabolic system to dump reduced nitrogen out of cells. This tricks the cells to degrade proteins without utilizing them for growth. Liao's team then removed the ammonia in the proteins and recycled it back for the growth of the algae they worked with. Algae, which can grow quickly, were used only as a carrier to assimilate carbon dioxide and produce protein, resulting in more CO2 fixation and growth. This strategy eliminates the use of expensive photo-bioreactors. More details appear in a recent paper in Nature Biotechnology.
The advantages of using proteins are numerous. Proteins are a major component in fast-growing microorganisms and their accumulation rate surpasses that of any raw material. The recalcitrance problems of lignocellulose or the dewatering problem of algal lipids don't surface in proteins. Compared to cellulosic biomass, which is difficult to break down, protein biomass can be much more easily digested for microorganism use.
However, challenges remain in protein-based biorefining. The researchers note it has been difficult to effectively convert protein hydrolysates to fuels and chemicals.
"Microorganisms tend to use proteins to build their own proteins instead of converting them to other compounds," says Yi-xin Huo, a postdoctoral researcher and lead author of the study. "So to achieve the protein-based biorefining, we have to completely redirect the protein utilization system, which is one of the most highly regulated systems in the cell."
Further, Liao notes large-scale algae production and nitrogen recycling "will certainly introduce new and unknown challenges."
"We are currently testing conditions for open algae culture in preparation for large-scale cultures. The laboratory experiment will take at least two years," he adds.
While current research focuses on using proteins for alcohols as a proof of principle, Liao says that making other compounds, such as bulk chemicals, monomers and pharmaceutical intermediates should follow without much of a scientific barrier.
The current process achieves 56% of the theoretical yield for the protein-to-alcohol conversion. Liao believes a mature process could reach 85–95% of the theoretical yield.
Compared to other biomass-based alcohol routes, Liao predicts the cost of the new protein process will be lower "because the process avoids the difficult lignocelluloses deconstruction problem."
Liao expects to reach pilot-plant stage in three to five years, but says large-scale commercialization could take more than 10 years.