The Effects of Temperature and Growth Phase on the Lipidomes of Sulfolobus islandicus and Sulfolobus tokodaii.

The functionality of the plasma membrane is essential for all organisms. Adaption to high growth temperatures imposes challenges and Bacteria, Eukarya, and Archaea have developed several mechanisms to cope with these. Hyperthermophilic archaea have earlier been shown to synthesize tetraether membrane lipids with an increased number of cyclopentane moieties at higher growth temperatures. Here we used shotgun lipidomics to study this effect as well as the influence of growth phase on the lipidomes of Sulfolobus islandicus and Sulfolobus tokodaii for the first time. Both species were cultivated at three different temperatures, with samples withdrawn during lag, exponential, and stationary phases. Three abundant tetraether lipid classes and one diether lipid class were monitored. Beside the expected increase in the number of cyclopentane moieties with higher temperature in both archaea, we observed previously unreported changes in the average cyclization of the membrane lipids throughout growth. The average number of cyclopentane moieties showed a significant dip in exponential phase, an observation that might help to resolve the currently debated biosynthesis pathway of tetraether lipids.

Liposomes containing lipids from Sulfolobus islandicus withstand intestinal bile salts: An approach for oral drug delivery?

In an attempt to design an oral drug delivery system, suited to protect labile drug compounds like peptides and proteins against the harsh environment in the stomach and upper intestine, we have prepared liposomes from phospholipids, cholesterol and archaeal lipids. As source for the archaeal lipids we used Sulfolobus islandicus, a hyperthermophilic archaeon, whose lipids have not been used in liposomes before. Culturing conditions and extraction protocols for its membrane lipids were established and the lipid composition of the crude lipid extract was characterized. The extracted membrane lipid fraction of S. islandicus consisted primarily of diether lipids with only a small fraction of tetraether lipids. Small unilamellar liposomes with 18% (mol/mol) of crude archaeal lipid extract were from S. islandicus were produced, for the first time and proven to be stabilized against aggressive bile salts as determined by loss of entrapped marker (calcein). At 4.4mM taurocholate (physiological taurocholate level) liposomes containing archaeal lipids retained entrapped marker better than liposomes made of egg phosphatidylcholine (PC) alone and to an extent similar to liposomes made of egg PC and cholesterol. Our findings showed that crude archaeal lipid extracts have, to a certain extent, stabilizing effects on liposomes similar to purified tetraether lipid fractions tested previously.

Structural characterization of ether lipids from the archaeon Sulfolobus islandicus by high-resolution shotgun lipidomics.

The molecular structures, biosynthetic pathways and physiological functions of membrane lipids produced by organisms in the domain Archaea are poorly characterized as compared with that of counterparts in Bacteria and Eukaryota. Here we report on the use of high-resolution shotgun lipidomics to characterize, for the first time, the lipid complement of the archaeon Sulfolobus islandicus. To support the identification of lipids in S. islandicus, we first compiled a database of ether lipid species previously ascribed to Archaea. Next, we analyzed the lipid complement of S. islandicus by high-resolution Fourier transform mass spectrometry using an ion trap-orbitrap mass spectrometer. This analysis identified five clusters of molecular ions that matched ether lipids in the database with sub-ppm mass accuracy. To structurally characterize and validate the identities of the potential lipid species, we performed structural analysis using multistage activation on the ion trap-orbitrap instrument as well as tandem mass analysis using a quadrupole time-of-flight machine. Our analysis identified four ether lipid species previously reported in Archaea, and one ether lipid species that had not been described before. This uncharacterized lipid species features two head group structures composed of a trisaccharide residue carrying an uncommon sulfono group (-SO3) and an inositol phosphate group. Both head groups are linked to a glycerol dialkyl glycerol tetraether core structure having isoprenoid chains with a total of 80 carbon atoms and 4 cyclopentane moieties. The shotgun lipidomics approach deployed here defines a novel workflow for exploratory lipid profiling of Archaea.