Metabolism of n-alkadienes in the a race ofBotryococcus braunii

Abstract An efficient metabolism of erogenous n -alkadienes was shown to occur in the A race (alkadiene-producing) of Botryococcus braunii . Several groups of very long chain lipids including two series of GC-amenable compounds, n -alkadienones and n -alkenylepoxides, were thus formed. Such a metabolism results from direct transformations of hydrocarbons and no prior degradation into short units is involved. Alkadiene transformation takes place from a very small ‘metabolic’ pool, distinct from the large pools (external in outer walls and internal in cytoplasmic inclusions) where B. braunii hydrocarbons are almost exclusively located. Hydrocarbons in the two latter pools are irreversibly stored and not further metabolized. Formation of n -alkenylepoxides from alkadienes is a normal feature of B. braunii metabolism when grown in an entirely mineral medium. In sharp contrast, formation of n -alkadienones only occurs when alkadienes are added to the culture medium. This pathway is probably induced by the large increase in the size of the ‘metabolic’ hydrocarbon pool due to entry of exogenous dienes. The insoluble and chemically resistant biopolymer of outer walls (PRB A) is probably formed via increasing condensation of high M r , lipids derived from very long chain compounds, such as n -alkenylepoxides. Alkadiene metabolism thus contributes both to the formation of the complex mixture of lipids typical of the A race of B. braunii and to the formation of the polymethylenic chains building up the polymeric network of PRB A.