Gene deletions leading to a reduction in the number of cyclopentane rings in Sulfolobus acidocaldarius tetraether lipids

The cell membrane of (hyper)thermophilic archaea, including the thermoacidophile Sulfolobus acidocaldarius, incorporates dibiphytanylglycerol tetraether lipids. The hydrophobic cores of such tetraether lipids can include up to eight cyclopentane rings. Presently, nothing is known of the biosynthesis of these rings. In this study, a series of S. acidocaldarius mutants deleted of genes currently annotated as encoding proteins involved in sugar/polysaccharide processing were generated and their glycolipids were considered. Whereas the glycerol-dialkyl-glycerol tetraether core of a S. acidocaldarius tetraether glycolipid considered here mostly includes four cyclopentane rings, in cells where the Saci 0421 or Saci 1201 genes had been deleted, species containing zero, two or four cyclopentane rings were observed. At the same time, in cells lacking Saci 0201, Saci 0275, Saci 1101, Saci 1249 or Saci 1706, lipids containing mostly four cyclopentane rings were detected. Although Saci 0421 and Saci 1201 are not found in proximity to other genes putatively involved in lipid biosynthesis, homologs of these sequences exist in other Archaea containing cyclopentane-containing tetraether lipids. Thus, Saci 0421 and Saci 1201 represent the first proteins described that somehow contribute to the appearance of cyclopentane rings in the core moiety of the S. acidocaldarius glycolipid considered here.