GROWTH AND BRANCHED HYDROCARBON PRODUCTION IN A STRAIN OF BOTRYOCOCCUS BRAUNII (CHLOROPHYTA)1

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Abstract
A strain Botryococcus braunii Kütz. that produces high levels of branched hydrocarbons (botryococcenes) was grown under different environmental conditions to investigate the relationship between growth and hydrocarbon production. Carbon dioxide concentration had the most significant influence on growth; 0.3% CO2‐enriched cultures demonstrated a minimum mass doubling time of ca. 40 h, compared to ca. 6 days for ambient air cultures grown on the same buffered growth medium. The botryococcene fraction, which consisted of 10 identified compounds (CnH2n‐10; n = 30–34), usually constituted ca. 25–40% of the culture dry weight under various growth regimes, including nitrogen‐ and/or phosphate‐deficiencies. CO2 enrichment initially favored the production of the lower botryococcenes (C30–C32), whereas relatively slow‐growing ambient air cultures accumulated C33 and C34 compounds.Colony color changed in response to different light intensities. High light increased the carotenoid/chlorophyll ratio, which resulted in orange colonies. Cultures exposed to low light intensity appeared green. This change in coloration was reversible over a period of a few days, and at no time were the linear hydrocarbons characteristic of the other form of the alga detected. Ostensible colony color is not, therefore, a reliable indicator of qualitative hydrocarbon content.Sequential solvent extraction experiments indicated that up to ca. 7% of the botryococcene fraction was intracellular and that the remainder was located within the colonial matrix. The internal (cellular) pool principally consisted of C30–C32 botryococcenes, whereas the external (colonial matrix) pool contained >99% of the C33 and C34 compounds, in addition to large amounts of the lower botryococcenes. These results, taken in conjunction with other data, are compatible with the hypothesis that the C30 botryococcene is the precursor, presumably via methylation, of the higher botryococcenes.