Canadian researchers propose ways of harvesting oil from diatoms, using biochemical engineering and also a new solar panel approach that utilizes genomically modifiable aspects of diatom biology, offering the prospect of “milking” diatoms for sustainable energy by altering them to actively secrete oil products. Secretion by and milking of diatoms may provide a way around the puzzle of how to make algae that both grow quickly and have a very high oil content.
They review a simple line of reasoning: (a) geologists claim that much crude oil comes from diatoms; (b) diatoms do indeed make oil; (c) agriculturists claim that diatoms could make 10−200 times as much oil per hectare as oil seeds; and (d) therefore, sustainable energy could be made from diatoms.
The transparent diatom silica shell consists of a pair of frustules and a varying number of girdle bands that both protect and constrain the size of the oil droplets within, and capture the light needed for their biosynthesis. We propose three methods: (a) biochemical engineering, to extract oil from diatoms and process it into gasoline; (b) a multiscale nanostructured leaf-like panel, using live diatoms genetically engineered to secrete oil (as accomplished by mammalian milk ducts), which is then processed into gasoline; and (c) the use of such a panel with diatoms that produce gasoline directly.
NOTE: This is a specific proposal of something that seems promising, but for which there is a lot of research to prove and then more research to scale up and to make work. The research might proceed well, but it has not happened yet.
With more than 200,000 species from which to choose, and all the combinatorics of nutrient and genome manipulation, finding or creating the “best” diatom for sustainable gasoline will be challenging, the authors offer some guidelines for starting species:
Choose planktonic diatoms with positive buoyancy or at least neutral buoyancy.
Choose diatoms that harbor symbiotic nitrogen-fixing cyanobacteria, which should reduce nutrient requirements.
Choose diatoms that have high efficiency of photon use, perhaps from those that function at low light levels.
Choose diatoms that are thermophilic, especially for solar panels subject to solar heating.
Consider those genera that have been demonstrated by paleogenetics to have contributed to fossil organics.
For motile or sessile pennate diatoms that adhere to surfaces, buoyancy may be much less important than survival from desiccation, which seems to induce oil production. Therefore, the reaction of these diatoms to drying is a place to start. The reaction of oceanic planktonic species to drying has not been investigated, although one would anticipate that they have no special mechanisms for addressing this (for them) unusual situation.
Genetic engineering of diatoms to enhance oil production has been attempted, but it has not yet been successful.
Generally, cell proliferation seems to be counterproductive to oil production on a per-cell basis, which is a problem that has been expressed as an unsolved Catch-22. However, this balance may shift in our favor when we start milking diatoms for oil instead of grinding them.