Mono-, di- and trimethyl-branched alkanes in cultures of the filamentous cyanobacterium Calothrix scopulorum

The extractable lipids of the cyanobacterium Calothrix scopulorum contain a complex suite of mono-, di- and trimethylheptadecanes. We identified 21 is omers; most of them have not been reported previously. The major compounds are 4,13-, 5,13-, and 4,5-dimethyl-, and 4,5,13- and 4,5,14-trimethylheptad ecane. Methyl substitution occurs preferentially, but not exclusively, at p ositions 4 and 5 (or omega-4 and omega-5) at either end of the carbon chain . In mass spectra, the location of methyl groups at opposite ends of the ca rbon chain can be deduced from the presence of a characteristic secondary C nH2n-1+ fragment ion. The interpretation of mass spectra was confirmed by c alculated retention index values which closely match the measured data. Our data provide evidence that branched alkanes with 17 to 20 carbon atoms can be used as biomarkers for cyanobacterial contributions to sedimentary orga nic matter. (C) 1999 Elsevier Science Ltd. All rights reserved.