Collaborative Research: Engineering of Recoverable Cellulosomes for Bioconversion

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The sustainable, industrial-scale production of transportation biofuels from plant biomass rely on enzymes called cellulases that break down the cellulosic fraction of biomass into sugars that can be fermented into bioethanol. The major cost of this process is the cellulase, which in the current generation of cellulosic biofuel facilities, is discarded after use because it must be dissolved in water to break down cellulose to sugars, and cannot be easily recovered. Recycling the cellulase enzyme would reduce the cost of cellulosic biofuels production. The goal of this project is to develop a new way of encapsulating the cellulase enzyme in recoverable solid form so that it can be collected reused multiple times before disposal. The key innovation is to bind the cellulase enzyme to nanometer-sized capsule called a cellulosome, which preserves the activity of the enzyme for cellulose conversion, and has a magnetic core which facilitates its recovery from dilute water processing streams. The educational activities associated with this project include mentoring of undergraduate student projects coordinated through the Nurturing American Tribal Undergraduate Research and Education (NATURE) program at North Dakota State University.Microorganisms that naturally produce cellulase enzymes bind them into special structures on the cell surface called cellulosomes. Due to the close proximity of these enzymes within the cellulosomes, the bioconversion of cellulosic and hemicellulosic materials proceeds with a high velocity and efficiency. However, in the industrial production of celluloytic enzymes, the cellulosome is not present. This research will engineer recoverable cellulosomes through a biomimetic approach where celluloytic enzymes are encapsulated within a nanstructured capsule containing a magnetic core. This biomimetic cellulosome will contain a number of complimentary celluloytic enzymes confined within a polymeric environment, and will be engineered to mimic several key properties of natural cellulosomes, including diversity of hydrolytic activity, close proximity of complementary enzymes, and strong and selective binding of the biomimetic cellulosome to cellulosic substrates. The magnetic core of the biomimetic cellulosome will facilitate its recovery from liquid suspension using magnetic separation techniques. To explore the potential of the biomimetic cellulosome for biomass conversion processes, the research has four objectives. The first objective is to make a series of new biomimetic cellulosomes to enhance synergism of hydrolytic enzymes for bioconversion of cellulosic materials to sugars. The second objective is to quantify the effects of the biomimetic cellulosome structure and immobilized enzyme diversity on cellulose hydrolysis to gain a fundamental understanding of cellulase synergism in natural cellulosomes. The third objective is to gain a fundamental understanding of cellulosome interaction with cellulosic substrates and lignin, and the fourth objective is to augment the functionality of the biomimetic cellulosome for broader applications. The anticipated outcomes from these studies include a fundamental understanding of the synergism of enzymes in engineered cellulosomes, their efficacy for different forms of substrates, and their potential for recovery and reuse.