Structural characterization, occurrence and fate of archaeal ether-bound acyclic and cyclic biphytanes and corresponding diols in sediments

Acyclic and cyclic biphytane carbon skeletons derived from planktonic archaea have been investigated in a number of marine and lacustrine sediments. With the exception of a tricyclic biphytane, the structures have been identified using authentic standards obtained from the thermophilic archaeon Sulfolobus solfataricus. The tricyclic biphytane, which is different to that biosynthesized by S. solfataricus, was tentatively identified based on mass spectral data. These acyclic and cyclic biphytanes occur ether-bound at the α and ω positions and as free and ester-bound α,ω-diols. Artificial maturation experiments show that the acyclic biphytane can endure greater thermal stress than cyclic biphytanes, in accordance with the occurrence of the acyclic biphytane in petroleum but absence of cyclic biphytanes. Compound specific isotope analysis reveals that the biphytanes all have similar 13C-contents to each other, even among different sediments. The acyclic biphytane sometimes differs in 13C-contents compared to the cyclic biphytanes, suggesting an additional source for this compound, possibly methanogenic archaea. Acyclic and cyclic biphytanes are sometimes the most abundant lipids in sediments compared to those biosynthesized by eukaryotes and prokaryotes, indicating that pelagic archaea can be a much more important source of sedimentary lipids than thought previously.