Botryococcus braunii

Botryococcus braunii (Bb) is a green, pyramid shaped colloidal microalgae of the order Chlorococcales (class Chlorophyceae) that is of potentially great importance in the field of biotechnology. Colonies held together by a lipid biofilm matrix can be found in temperate or tropical oligotrophic lakes and estuaries, and will bloom when in the presence of elevated levels of dissolved inorganic phosphorus. The species is notable for its ability to produce high amounts of hydrocarbons, especially oils in the form of fatty acids, that are typically around 30-40 percent of their dry weight.^[1] Compared to other green algae species it has a relatively thick cell wall that is accumulated from previous cellular divisions; making extraction of cytoplasmic components rather difficult. Fortunately, much of the useful hydrocarbon oil is outside of the cell.

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Optimal growth environment

Botryococcus braunii has been shown to grow best at a temperature of 23°C, a light intensity of 60 W/M², with a light period of 12 hours per day, and a salinity of 0.15 Molar NaCl.^[2] However, this was the results of testing with one strain, others certainly vary to some degree.

Potential biofuel application

The hydrocarbons this species produces can be chemically converted into fuels. Transesterification can be used to make biodiesel or it can be used as feedstock for hydrocracking in an oil refinery where fatty acid chains to produce octane (gasoline, a.k.a. petrol), kerosene, and diesel.^[3]

Oils

Two major races of Bb are known, and they are distinguished by the structure of their hydrocarbons. These have the formula C_nH_2n-10. The A race produces odd, unbranched hydrocarbons n = 23 through 31 and the B race produces n = 30 through 37 isoprenoid hydrocarbons known as Botryococcenes. Within this major classification, various strains of Bb will differ in the precise structure and concentrations of the constituent hydrocarbons.^[4]

According to p. 30 on Aquatic Species Program (ASP) report,^[5] Botryococcus would not function well as a feedstock for lipid based fuel production due to its slow growth (one doubling every 72 hours). However, subsequent research by Qin showed that the doubling time could be reduced to 48 hours in its optimal growth environment.^[2] The ASP also found Botryococcus oil to be less than ideal, having most of its lipids as C₂₉ to C₃₄ aliphatic hydrocarbons, and less abundance of C₁₈ fatty acids. This evaluation of Bb oils was done in relation to their suitability for transesterification (i.e. creating biodiesel), which was the focus of the ASP at the time Bb was evaluated. The ASP did not study Bb oils for their suitability in hydrocracking, as some subsequent studies have done.

Patented strains

In 1986, UCBerkeley was granted US Plant Patent 6169for a strain of Botryococcus braunii it developed. Their proprietary strain was notable, says the patent application, because of its fast growth rate and high oil content. However, it is not clear as to whether Bb Showa was in fact more productive than strains which have been subsequently identified. There is no evidence of commercial exploitation of the patent, and it expired in April 2006.

References