Abstract

Background: Photosynthetic diatom microalgae have significant capacity for biosynthesis of energydense biofuel molecules, as well as unique co-products not found in other 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.

Objectives: To exploit their silicon metabolism for eliciting the biosynthetic pathways of selected products, a two-stage cultivation process is developed to induce high levels of lipid and chitin production by the centric marine diatom Cyclotella within a bubble-column photobioreactor under conditions were light and CO₂ delivery are not limiting.

Methods and Results: The two-stage batch cultivation process synchronized Cyclotella diatom cells to silicon-starved state in Stage I and reduced the time to silicon depletion in Stage II biomass production by surge uptake of dissolved silicon. Lipid and chitin production were elicited at silicon depletion but not at nitrogen depletion. Stage II product yields associated with the biomass were 34 wt% total lipid and 16 wt% chitin, with 60% of total biomass carbon allocated to these two products. From this information, a material balance on the diatom-based photosynthetic bio-refinery for production of the nutraceutical glucosamine with co-production of biodiesel and biosilica illustrated the productivity of this biological production system.

Conclusion: The diatom-based photosynthetic biorefinery has significant potential as a future platform for biofuels and unique co-products.

Keywords: Biorefinery, chitin, diatom, glucosamine, lipid, photobioreactor.

Graphical Abstract