Chemical inhibition of resistant biopolymers in outer walls of the A and B races of Botryococcus braunii

Abstract

The influence of SC 1058, a cinnolinyl compound recently shown to inhibit the formation of exines of pollen grains, was studied in the A and B races of Botryococcus braunii. A pronounced inhibition of the non-hydrolysable biopolymers (PRB A and PRB B, respectively) building up their thick basal outer walls was observed in the two races regarding both mass and labelling from acetate. This strong decrease in PRB formation was achieved using SC 1058 concentrations which did not inhibit B. braunii primary metabolism and the total biomass of the cultures was not substantially affected. Decrease in PRB formation in the two races is associated with a marked inhibition of the external lipids, whereas the internal lipids are sharply stimulated. However, the total production of lipids is not affected much by SC 1058; this compound therefore induces a marked shift in lipid distribution between external and internal pools. The effect of SC 1058 on external and internal lipids (inhibition and stimulation, respectively), is more pronounced in the A race when compared with the B race. A strong inhibition of the external hydrocarbons, n-alkadienes and n-alkatrienes, was noted in the A race. All these observations on the influence of SC 1058 are consistent with (i) the marked differences in the composition of external lipids and in their assumed implication in PRB biosynthesis between the two races, (ii) the existence of tight biosynthetic relationships in the A race between PRB A, n-alkenes and other groups of very long-chain non-isoprenoid lipids located in the external pool and (iii) the complete lack of relationships between hydrocarbons (botryococcenes) and PRB in the B race. A strong decrease of lipid transport from the internal to the external pool, especially affecting the precursor(s) implicated in the formation of very long-chain non-isoprenoid lipids, and hence of PRB, is a major feature of SC 1058 influence on the two races of B. braunii. Electron microscopic observations on the A race revealed that inhibition of PRB A formation is associated with pronounced changes in the ultrastructure and rigidity of its outer walls.