(772b) Bioprocessing Strategies for Engineered Coproduction of Biofuels and Medical Biopolymers from Diatom Microalgae

Photosynthetic diatom microalgae have significant capacity for biosynthesis of energy-dense biofuel molecules, as well as unique valued co-products not found in other types of algae, including metal oxide nanomaterials for advanced material applications, and glucosamine biopolymers or monomers for nutraceutical and biomedical applications. Diatoms biomineralize soluble silicon to nanostructured biosilica, and require dissolved silicon (Si) as a required substrate for cell wall biosynthesis and division. Bioprocess engineering strategies have the potential to guide the cellular biosynthesis of three aforementioned product streams, all within the same diatom cell. To exploit diatom silicon metabolism for eliciting the biosynthetic pathways of selected products, a two-stage cultivation process was developed to induce high levels of lipid and chitin production by the centric marine diatom Cyclotella within under tightly controlled conditions where light and CO₂ delivery are not limiting. Carbon dioxide delivery and consumption were measured in real time to determine carbon flux into biomass, lipid, and chitin biopolymer products. The two-stage cultivation process synchronized Cyclotella diatom cells to silicon-starved state in Stage I. In Stage II, the cells were maintained in a nominal silicon-starved state under controlled nutrient perfusion, which allowed for continued cell division, carbon dioxide assimilation, and product formation. In this cultivation mode, cell biomass, lipid, and chitin production were elicited and linearly maintained at silicon depletion without the need for nitrogen depletion. Intracellular accumulation of lipid and extracellular extrusion of chitin microfibrils were evident. Optimal stage II product yields associated with the biomass were 34 wt% total lipid and 16 wt% chitin, with 60 mol% of assimilated carbon dioxide allocated to these two products. From this information, a process flowsheet and material balance on the diatom-based photosynthetic bio-refinery for production of the nutraceutical glucosamine with co-production of biodiesel and biosilica was developed to illustrate the productivity at scale. This analysis shows that the diatom-based photosynthetic biorefinery has significant potential as a future platform for biofuels and unique, valuable co-products.