Abstract
The green alga Botryococcus braunii produces abundant hydrocarbons, in the form of drop-in biodiesel, which promoted interest in the species as a renewable fuel. However, despite the observation of dense populations in the wild, Botryococcus grows very slowly in culture, severely limiting its potential for development as a bioresource. Undertaking a biodiscovery program, we found new strains of Botryococcus in locations ranging from tropical to temperate Australia and from both fresh and brackish waters. As part of the ecophysiological characterisation of this new biodiversity, lipid and pigment compositions were studied for six new strains from six different locations. The strains were inoculated in either freshwater or brackish (salinity of 4)-based medium and maintained over 150 days. The growth of cultures was studied continuously, while lipid and pigment composition were analysed at final harvest on day 150. No significant differences in growth rate between fresh and brackish media were observed. Some strains were more tolerable of brackish conditions than others with a link between salinity tolerance and original location. The use of lower salinity (4 ppt) had a minimal effect on lipid composition, with only two of the six strains showing a different hydrocarbon profile in comparison to the other strains; pigment composition showed only minor variations for fresh and brackish water cultures, although the concentrations varied significantly with the freshwater cultures containing higher pigment concentrations.
Highlights
Botryococcus braunii is a green algae (Trebuxiophyceae) that is characterised by its ability to produce up to 61% of its dry weight as a hydrocarbon-rich oil that is composed of non-oxygenated hydrocarbons [1,2,3]
The availability of endemic B. braunii strains from culture collections and obtaining key information for the optimisation of growth conditions will be required for any future commercial production of this sought–after group, including for biotechnology and bioactivity applications
This study is part of an effort to characterise six new endemic Australian B. braunii strains obtained from different locations and to investigate the effects of salinity on their growth, hydrocarbon, and pigment compositions
Summary
Botryococcus braunii is a green algae (Trebuxiophyceae) that is characterised by its ability to produce up to 61% of its dry weight as a hydrocarbon-rich oil that is composed of non-oxygenated hydrocarbons [1,2,3]. The interest in studying B. braunii has been due to its geochemical significance in a variety of oil-rich deposits throughout the world dating from the Ordovician (485.4–443.7 mya). When the hydrocarbon-rich oil from B. braunii was “cracked” (the catalytic and thermal degradation of long chain hydrocarbons to form useable shorter chain hydrocarbons), it yielded. A key feature of the physiology of B. braunii is the hydrocarbon-rich oil that is excreted in the form of long-chain (defined as ≥C23 ) aliphatic hydrocarbons from the cells into the extracellular matrix, which in turn is encased in the retaining wall [3]. Strains of race A are characterised by n–alkadienes and/or n–alkatrienes and their derivatives with an odd carbon number (C23–33 ); Race B produces a range of specific botryococcenes that are Cn H2n–10 triterpenes (C30 –C37 ) and methylated squalenes (C31 –C34 ); Race L produces lycopadiene—a single tetraterpenoid hydrocarbon not formed by other strains of
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