A C25 highly branched isoprenoid alkene and C25 and C27 n-polyenes in the marine diatom Rhizosolenia setigera

A North Atlantic strain of the marine diatom Rhizosolenia setigera was examined for the presence of hydrocarbons. This strain biosynthesizes a highly branched isoprenoid (HBI) C25 pentaene, in contrast to Australian strains of R. setigera which produce HBI C30 alkenes. The more widespread occurrence of C25 HBI alkenes compared to their C30 counterparts in sea water and sediments may reflect the fact that C25 HBI alkenes occur both in Haslea and R. setigera. The North Atlantic R. setigera strain also biosynthesizes C25 and C27 n-polyenes with six or seven double bonds in relatively high amounts. Their carbon number distribution was found to depend on growth temperature. These lipids may be the precursors for C25 and C27 2-n-alkylthiophenes, which are important organosulfur compounds in sediments from palaeo upwelling regions. The distribution of these thiophenes may have potential for reconstruction of palaeo sea surface temperatures.