Intact phospholipids—microbial “life markers” in marine deep subsurface sediments

Deep subsurface sediments from the Nankai Trough, Japan Sea, ODP Leg 190, sites 1173, 1174, 1177, and near-surface sediments from Hydrate Ridge, NE-Pacific have been analysed by high performance liquid chromatography (HPLC)–electrospray ionisation (ESI)-mass spectrometry (MS). The main objective was to utilize the presence of intact phospholipids as a direct indicator of viable microorganisms. The extracts of Nankai Trough sediments were found to contain a variety of phospholipid (PL) structures, well-known to stem from microorganisms, to depths as great as 745 mbsf and in situ temperatures as high as 85 °C. In addition, high relative amounts of lysophospholipids (e.g. lysophosphatidylcholines) exceeding those of the regular phospholipids were detected. Diglyceride mass fragments of various PLs have been assigned to fatty acyl side-chains of typical chain length (C14, C16, C18, C20) and degree of unsaturation (zero, one or two double bonds). Similar results were obtained for the phospholipid distribution in extracts of organic matter-rich Hydrate Ridge sediments. To date, the enhanced occurrence of lysophospholipids cannot be explained completely but a response to increasing thermal and ecological stress seems probable.