The resistant polymer of the walls of the hydrocarbon-rich alga Botryococcus braunii

The outer walls of the green alga Botryococcus braunii (main sites of hydrocarbon production and accumulation) show a complex constitution. They comprise a biopolymer highly resistant to non-oxidative degradation. The resistant polymer accounts for ca 9% of the cell dry wt and appears, along with hydrocarbons, as one of the major constituents of the alga. In addition to chemical resistance, B. braunii polymer exhibits other properties: mode of deposition and fluorescence, often used to identify sporopollenins. (Class of wall components generally regarded as originating from polymerization of carotenoid derivatives.) Nevertheless further studies, using IR spectroscopy and high resolution ¹³C NMR of solids, along with determination of elemental composition and unsaturation levels, indicate that the bulk of the resistant polymer from B. braunii outer walls does not derive from carotenoids; accordingly it cannot be considered, in this respect, as a sporopollenin. In fact the information obtained on the structure of this important constituent of the alga is consistent with its formation via oxidative polymerization of B. braunii dienic hydrocarbons.