Biochemical implications and geochemical significance of novel phospholipids of the extremely barophilic bacteria from the Marianas Trench at 11,000 m

The membrane phospholipids of two barophilic bacteria, DB21MT-2 and DB21MT- 5, isolated from sediments from the Marianas Trench at 11,000 m were struct urally characterized and quantitatively determined by liquid chromatography /electrospray ionization/mass spectrometry (LC/ESI/MS). Phospholipids detec ted in the barophiles were distributed in five different classes: phosphati dylglycerol (PG), phosphatidylinositol (PI), phosphatidylcholine (PC), diph osphatidylglycerol (DPG), and phosphatidylethanolamine (PE) and its methyla ted forms phosphatidylmethylethanolamine (PME) and phosphatidyldimethyletha nolamine (PDME). Concentrations of phospholipids/phospholipid groups range from 5.3 to 4.583 mu g/g (dry weight). A unique aspect of the phospholipid profiles of the barophilic bacteria was the wide distribution of polyunsatu rated fatty acids 20.5 (in DB21MT-2) and 22:6 (in both DB21MT-5 and DB1MT-2 ) on the sn-1 and mostly on the sn-2 position of the phospholipids. The res ults suggest that the adaptation of the barophiles to low temperature and h igh hydrostatic pressure influenced the synthesis of phospholipids containi ng polyunsaturated fatty acids. It was also observed that the polyunsaturat ed fatty acids were associated with almost every phosphatidylglycerol (PG) molecule. Presumably, the larger head group of PG would be expected to caus e greater disruption in acyl chain packing within the membrane bilayer and thereby lower the transition temperature in response to the additive effect s of law temperature and high pressure. The detection of phospholipids with polyunsaturated fatty acids also has important geochemical implications fo r paleoenvironment reconstruction and for determining the surface water bio logical productivity of the ocean. It seems that psychrophilic and barophil ic bacteria may be major sources of polyunsaturated fatty acids to the deep -sea sediments, given the fact that the vertical flux of polyunsaturated fa tty acids from surface water plankton decreased rapidly with depth. (C) 200 0 Elsevier Science Ltd. All rights reserved.