Novel ether lipid cardiolipins in archaeal membranes of extreme haloalkaliphiles.

The lipidome of two extremely haloalkaliphilic archaea, Natronococcus occultus and Natronococcus amylolyticus, has been examined by means of combined thin-layer chromatography and MALDI-TOF/MS analyses. The detailed investigation of lipid profiles has confirmed the presence of i) ether lipid phosphatidylglycerol and phosphatidylglycerophosphate methyl ester as main lipid components, ii) both C(20) and C(25) isopranoid chains in the lipid core and yielded new findings on membrane lipids of these unusual organisms. Besides some novel minor or trace phospholipids and glycolipids, data indicate the presence of ether lipid cardiolipin variants constituted by different combinations of C(20) and C(25) isopranoid chains, never before described in archaea. The role of C(25) isopranoid chains in the adaptation to high pH gradients in the presence of very high salt concentrations is discussed.

Control of ribosome turnover during growth of the haloalkaliphilic archaeon Natronococcus occultus.

The metabolism of ribosomes during growth of the haloalkaliphilic archaeon Natronococcus occultus was examined. The ribosome content was higher during exponential growth and diminished to 35% of the maximum in the stationary stage. The incorporation of H3-orotic acid and C14-uracil into rRNA was higher during exponential growth. After that, it decreased to 39% of the maximum in the stationary stage. The labeling of non-ribosomal RNA took place almost exclusively in the exponential stage. From loss of radioactivity, the half-life of rRNA was 11.43, 14.85, 5.28 and 7.14 h during the initial, exponential, late exponential and stationary growth stages, respectively. These results suggested that increased synthesis combined with diminished degradation were responsible for the high ribosome content displayed by Ncc. occultus during exponential growth. In contrast, diminished synthesis together with increased degradation provoked its posterior loss.

Ubiquitin-like proteins in halobacteria.

Within our studies of protein degradation, the presence of ubiquitinylated proteins in haloalkaliphilic archaea was investigated. We found that Natronococcus occultus proteins that react with antibodies raised against ubiquitin appear in different growth phases, particularly in the initial and exponential ones. The expression of these proteins is increased when the cells are either treated with puromycin or starved for nutrients. Dot blot analysis of cell extracts with antibody against ubiquitin shows the presence of either ubiquitinylated or ubiquitin-like proteins not only in Natronococcus occultus, but also in various genera of halobacteria.