Notes on diatoms

Posted by Stella Kin

• Diatoms are a kind of unicellular algae belonging to the algal class Bacillariophyceae.
• Diatoms are responsible for about one-fifth of the photosynthesis carried out on earth, and, like other
  primary producers, sequester carbon.They are estimated to fix at least 25-30% of the global carbon dioxide. 
• Under culture conditions, algal populations can double in size in a few hours, and are more effective absorbers of carbon than higher plants.
• Theoretical calculations based on the photosynthetic ability and growth potential of diatoms have
  shown that diatoms can yield more than 30,000 litres (or 200 barrels) of oil per hectare per annum. 
• Traditionally used crops for the production of biofuels such as oilseeds have an oil content of lesser than 5% of their total mass. Diatoms can yield 100–200 times as much oil as soybean, 10–200 times more than oil seeds and 7–31 times more than oil palm, which is considered as the next best source of oil1.
• Scientists have also found out that diatoms produce more oil (double or even triple the amount produced normally) under photo-oxidative stress or nutrient starvation such as lower nitrogen or silica content in the growth media. This is due to the shift in lipid metabolism from membrane lipid synthesis to the storage of neutral lipids
• the ‘pure’ diatom oil contains an estimated 60–70% saturates. The diatom oils are likely to be rich in fatty acids, which during early diagenesis, reportedly transform into condensed lipids1’.
• Ramachandra and his group have worked out a concept which ‘cuts down’ the time required to produce oil from diatoms from ‘millions of years to daily’. 
• They have suggested a way in which diatoms can be made to work like mammalian glands, so that one can ‘milk’ oil from them continuously for long periods of time. The diatoms will be designed such that they secrete the oil that they produce rather than store it, so that they need not be destroyed to obtain oil, and a continuous supply of oil is ensured. 
• ‘Milking’ diatoms would serve to do away with the cumbersome process of extraction of oil
  from them.
• The team has also proposed the design of a solar panel based on the structure of an angiosperm leaf – the epidermis, the outermost layer of the leaf, would be the solar panel; the inner tissues of the leaf, such as the palisade and spongy tissues that are responsible for much of the carbon fixation and photosynthesis, will be the photosynthetic diatoms

• Conditions for optimum production of oil will be provided. 
• Additionally, they have also suggested genetic manipulation of diatoms so that they produce gasoline directly instead of ‘crude oil’ from which gasoline must then be obtained. 
• In other words, they have envisioned a ‘solar panel that converts photons to gasoline rather than electricity or heat’1.

• The first step is to culture various diatoms and identify species that have higher oil content, and those that have a faster growth in low cost growth media. Also required are diatoms that would be thermophilic (they must be able to survive high temperature conditions of the solar panel), able to survive in the hydrocarbon mixture that they would exocytose, and have a highly efficient photosynthetic capacity. 
• The second step is the design of the solar panel and genetic modification of the diatoms to get a system that would give a continuous supply of oil. Ramachandra et al. have also suggested the engineering of an angiosperm leaf with a symbiotic association with diatoms – the diatoms can replace the photosynthetic mesophyll tissue of the leaf while the leaf helps in gaseous exchange and also provides a humid environment for the growth of diatoms. 
• Another step is the genetic engineering of diatoms to make them produce gasoline directly so that the secretion can be used without further processing and modification. 

These various ‘steps’ may take a number of years, or may even happen simultaneously through collaboration.

Reference
Milking diatoms – a new route to sustainable energy

The links in the article don't lead anywhere, here are the results of a search done within Newcastle's website:
‘UK dream team’ to develop algae biofuel