Mario De Rosa

Effects of temperature on ether lipid composition of Caldariella acidophila

The composition of the ether lipids of a strain of Caldariella acidophila, with respect to the different numbers of cyclizations of the biphytanyl components, is shown to differ between the various complex lipid classes, but the degree of cyclization increases systematically with the growth temperature in the range 75–89°. The problem of distinguishing adaptive from phyletic features in archaebacterial lipids is considered.

Effect of isoprenoid cyclization on the transition temperature of lipids in thermophilic archaebacteria

The plasma membrane of Caldariella acidophila, an extreme thermophilic archaebacterium, is characterized by unusual bipolar lipids. They are based on two C40 ω-ω′ biphytanyl residues, with up to four cyclopentane rings per chain linked to either two glycerols (symmetric lipid) or to one glycerol and to one branched-chain nonitol (asymmetric lipid). When C. acidophila is grown at various temperatures, these lipids show a degree of cyclization of the biphytanyl components which increases as the environmental temperature increases. The role of cyclization in determining the temperature adaptation is studied on three lipid samples presenting four, five and six cyclopentane rings per molecule, respectively. Differential scanning calorimetry on the dry asymmetric sample as well as conductance and capacitance measurements on black films have been performed. Both sets of measurements indicate the presence of thermal transitions, three in the hydrated compounds, two in the dry system. The latter are shifted towards higher temperature values as the number of cycles increases. Calorimetric measurements show that two of these transitions are strictly related to the presence of nonitol-containing polar heads. In fact, only a single 10-fold higher transition is detected in the homologous lipid bearing two glycerol polar heads, in the dry as well as in the hydrated form. It is suggested that the two higher-temperature thermal transitions, observed on warming the sample, are induced by the breaking of hydrogen bonds between the nonitol-containing polar heads. By contrast, the lower temperature transition, present only in the hydrated compound and similar to that exhibited by the symmetrical sample, is due to a partial melting of the hydrophobic core. The large change in capacitance observed near the higher transition points by lowering temperature would thus correspond to variations in the dielectric constant due to formation of hydrogen bonds.

Chemical structure of the ether lipids of thermophilic acidophilic bacteria of the Caldariella group

Abstract The lipids of the Caldariella group of extremely thermophilic acidophilic bacteria are based on a 72-membered macrocyclic tetraether made up from two C40 diol units and either two glycerol units or one glycerol and one nonitol. The C40 components have the 16,16′-biphytanyl skeleton and the detailed structure of three of them is established.

Structure of calditol, a new branched-chain nonitol, and of the derived tetraether lipids in thermoacidophile archaebacteria of the Caldariella group

Abstract A second category of membrane lipids in extreme thermoacidophile archaebacteria of the Caldariella group is based on the same type of macrocyclic tetraether, incorporating two 16,16′-biphytanyl chains, as those described earlier, but only one of the hydrophilic components is glycerol; the second hydrophilic component is calditol, a unique branched-chain nonitol. It is also shown that in the biphytanyl chains there can be up to 4 cyclopentane rings whose location is demonstrated.

Complex lipids of Caldariella acidophila, a thermoacidophile archaebacterium

Abstract Isoprenoid ether lipids are common to the ‘urkingdom’ archaebacteria, within which members of the Caldariella group of extreme thermoacidophiles and some methanogenic species have lipids based on macrocyclic tetraethers containing two 16,16′-biphytanyl chains. As a step towards closer classification, the complex lipids of Caldariella acidophila have been more fully characterized.

Structural regularities in tetraether lipids of Caldariella and their biosynthetic and phyletic implications

Abstract Individual di(biphytanyl) diglycerol tetraether lipids from thermoacidophile archaebacteria of the Caldariella series, with differently cyclized biphytanyl components, are separated and shown to have structures 8–12 , with the glycerol and biphytanyl components demonstrably both antiparallel and with partial assignments of stereochemistry. Tetraethers with alternative arrangements of the components are absent. The structures allow previous observations on these and related lipids to be rationalized both biosynthetically and phyletically.

13C-NMR assignments and biosynthetic data for the ether lipids of Caldariella

Abstract Fully assigned 13 C-NMR spectra confirm the C 40 (16,16 -biphytanyl) structures of the alkyl chains in the ether lipids of extreme thermoacidophile bacteria of the Caldariella group. The incorporations of 13 C- and 14 C- labelled acetate and mevalonate provide further structural confirmation and define their biosynthetic origin.

Regularity of isoprenoid biosynthesis in the ether lipids of archaebacteria

Abstract The location of paired and unpaired 13C atoms in the 16,16′-biphytanyl components of the lipids of Caldariella acidiophila following incorporation of acetate-[1,2-13C2] shows that the overall process of isoprenoid biosynthesis in this archaebacterial species follows a normal pattern and that the head-to-head linkage of the two tetraprenyl chains occurs stereoselectively.

Isoprenoids of Bacillus acidocaldarius

Abstract -The isoprenoids of Bacillus acidocaldarius , a notably acidophilic thermophilic organism, were investigated. Besides normal bacterial isoprenoids such as menaquinone and polyprenols, which latter were resolved in a-cis and a-trans fractions, and some minor components ( a-tertiary -prenols and the corresponding anhydroderivatives), not fully characterized, and probably ‘natural’ artefacts, we have isolated and characterized squalene and pentacyclic triterpene hydrocarbons belonging to the hopane class, which must be accounted as unusual. Radioactivity from mevalonate-[2- 14 C] is incorporated into hopene-b (the major triterpene component), thus establishing the origin of cyclized squalene derivatives in B. acidocaldarius as a result of de novo synthesis.

Lipid biogenesis in archaebacteria

Summary Archaebacteria, which at present comprise three phenotypes including halophiles, methanogens and thermophiles, have lipids characterized by unusual structural features that can be considered as specific taxonomic markers. Whereas all other hitherto known living organisms have membrane lipids based on ester linkages, all archaebacteria studied up to the present possess lipids based on ether linkages formed by the condensation of glycerol or more complex polyols with isoprenoid alcohols of 20, 25 or 40 carbon atoms. This presentation surveys the most important aspects of archaebacterial lipid biosynthesis, dealing in particular with the pathway of isoprenoid assembly, the mechanism of ether linkage formation and with the biogenetic origin of alcohols of low molecular weight.