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
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