Occurrence of hopanoid lipids in anaerobic Geobacter species

Geobacter metallireducens and G. sulfurreducens have been classified as strictly anaerobic bacteria which grow and thrive in subsurface and sediment environments. Hopanoids are pentacyclic triterpenoid lipids and are important for bacterial membrane stability and functioning. Hopanoids predominantly occur in aerobically growing bacteria of oxic environments. They rarely have been found in facultatively anaerobic bacteria and, to date, not at all in strict anaerobes. Our research shows that anaerobically grown G. metallireducens and G. sulfurreducens bacteria contain a range of hopanoid lipids, such as diploptene (i.e. hop-22(29)-ene) and hop-21-ene, and more complex, elongated hopanoids. In geological formations, diagenetic derivatives of hopanoids are widely used as biomarkers and are recognized as molecular fossils of bacterial origin. To date, these biomarkers have largely been interpreted as those derived from ancient oxic environments. Our findings presented here suggest that this interpretation needs to be re-evaluated. In addition to the origin in oxic environments, 'geohopanoids' may originate from ancient anaerobic environments as well.     

Bacterial triterpenoids of the hopane series from the methanotrophic bacteria Methylocaldum spp.: phylogenetic implications and first evidence for an unsaturated aminobacteriohopanepolyol

The hopanoid content of the two methanotrophic bacteria Methylocaldum szegediense and Methylocaldum tepidum was investigated. 35-Aminobacteriohopane-30R,31R,32R,33S, 34S-pentol and its 3beta-methyl homologue were present in both strains. In M. tepidum, they were accompanied by 35-aminobacteriohopane-31R,32R,33S, 34S-tetrol and its 3beta-methyl homologue. The side chain structure was identical to those previously reported from two other obligate methanotrophs, Methylococcus capsulatus and Methylomonas methanica. The two Methylocaldum species shared with the Methylococcus species the presence of 3beta-methylhopanoid as well as of a hopanoid releasing adiantol upon H(5)IO(6)/NaBH(4) treatment. A rare feature was in addition found in M. szegediense. The saturated hopanoids were accompanied by an unsaturated aminobacteriohopanepentol with a Delta(11) double bond. Comparison of the hopanoid fingerprints was in accordance with the close phylogenetic relationship of Methylococcus and Methylocaldum. The major difference was the absence of sterols in Methylocaldum which were always detected in the Methylococcus species.     

Ehrenasterol and biemnic acid; new bioactive compounds from the Red Sea sponge Biemna ehrenbergi

In continuation of our efforts to identify bioactive compounds from the Red Sea marine sponges, we have recently investigated the organic extract of the sponge Biemna ehrenbergi. This study resulted in the isolation of eight compounds including a new sterol, ehrenasterol (1), a new C₂₄-acetylenic acid, biemnic acid (2), together with six known compounds including a hopanoid, three steroids and two nucleosides. The isolated compounds were identified as (22E)-ergosta-22-ene-8,14-epoxy-3,7-dione (1), (E)-tetracos-8-en-5-ynoic acid (2), (22E)-ergosta-5,8,22-trien-7-one-3β-ol (3), 32,35-anhydrobacteriohopanetetrol (4), (24R)-ergosta-6,22-diene-5,8-epidioxy-3-ol (5), melithasterol B (6), thymidine (7) and 2′-deoxyuridine (8). The structures of the isolated compounds were assigned by different spectral data including 1D and 2D NMR (COSY, HSQC, and HMBC) and high-resolution mass spectrometry. Compound 1 displayed inhibition zone of 20 mm at 100 μg/disc against Escherichia coli in the disc diffusion assay. Similarly, compounds 2 and 4 displayed inhibition zones of 20 and 18 mm respectively against Candida albicans at the same concentration. Compounds 1–3 displayed weak cytotoxic activity against human colon adenocarcinoma (HCT-116) cancer cell line.     

Hopanoids are formed during transition from substrate to aerial hyphae in Streptomyces coelicolor A3(2)

Streptomyces coelicolor A3(2) contains a cluster of putative isoprenoid and hopanoid biosynthetic genes. The strain does not produce the pentacyclic hopanoids in liquid culture but produces them on solid medium when sporulating. Mutants defective in the formation of aerial mycelium and spores (bld), with the exception of bldB, do not synthesize hopanoids, whereas mutants, which form aerial mycelium but no spores (whi), do. The membrane condensing hopanoids possibly may alleviate stress in aerial mycelium by diminishing water permeability across the membrane.     

Occurrence of an Unusual Hopanoid-containing Lipid A Among Lipopolysaccharides from Bradyrhizobium Species

The chemical structures of the unusual hopanoid-containing lipid A samples of the lipopolysaccharides (LPS) from three strains of Bradyrhizobium (slow-growing rhizobia) have been established. They differed considerably from other Gram-negative bacteria in regards to the backbone structure, the number of ester-linked long chain hydroxylated fatty acids, as well as the presence of a tertiary residue that consisted of at least one molecule of carboxyl-bacteriohopanediol or its 2-methyl derivative. The structural details of this type of lipid A were established using one- and two-dimensional NMR spectroscopy, chemical composition analyses, and mass spectrometry techniques (electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry and MALDI-TOF-MS). In these lipid A samples the glucosamine disaccharide characteristic for enterobacterial lipid A was replaced by a 2,3-diamino-2,3-dideoxy-d-glucopyranosyl-(GlcpN3N) disaccharide, deprived of phosphate residues, and substituted by an α-d-Manp-(1→6)-α-d-Manp disaccharide substituting C-4′ of the non-reducing (distal) GlcpN3N, and one residue of galacturonic acid (d-GalpA) α-(1→1)-linked to the reducing (proximal) amino sugar residue. Amide-linked 12:0(3-OH) and 14:0(3-OH) were identified. Some hydroxy groups of these fatty acids were further esterified by long (ω-1)-hydroxylated fatty acids comprising 26–34 carbon atoms. As confirmed by mass spectrometry techniques, these long chain fatty acids could form two or three acyloxyacyl residues. The triterpenoid derivatives were identified as 34-carboxyl-bacteriohopane-32,33-diol and 34-carboxyl-2β-methyl-bacteriohopane-32,33-diol and were covalently linked to the (ω-1)-hydroxy group of very long chain fatty acid in bradyrhizobial lipid A. Bradyrhizobium japonicum possessed lipid A species with two hopanoid residues.     

Bacterial triterpenoids of the hopane series as biomarkers for the chemotaxonomy of Burkholderia, Pseudomonas and Ralstonia spp

Hopanoid fingerprints allowed to differentiate bacteria formerly connected to the genus Pseudomonas. Whereas all strains related to Pseudomonas and Ralstonia were devoid of any detectable hopanoid, these pentacyclic triterpenoids were found in the Burkholderia species and in related soil isolates, which contained as main hopanoid a bacteriohopanetetrol carbapseudopentose ether, accompanied by significant amounts of its novel Delta(6) unsaturated homologue. Unsaturated hopanoids represent an extremely rare feature in soil bacteria and the only known indication for a catabolism of this pentacyclic carbon skeleton in bacteria.     

Analysis of hopanoids in bacteria involved in food technology and food contamination

Hopanoids are pentacyclic triterpenoids which are believed to act as reinforcers of membranes in certain prokaryotic microorganisms. A rapid and sensitive method for their screening in bacteria was elaborated, involving extraction of non-saponifiable lipids and the analysis by gas chromatography-mass spectrometry, selectively monitoring the ion of m/z=191. Using the method, hopanoids were detected in strains of Acetobacter pasteurianus, but were found to be absent in lactic acid bacteria (Lactobacillus spp., Lactococcus spp.) and in food-contaminating bacteria (Salmonella spp., Listeria spp., Yersinia spp. and others).     

Hopanoids of a recent sediment from Lake Constance as eutrophication markers

Abstract Bio- and geohopanoid distributions with depth from the upper sediment layers (25 cm) of Lake Constance (Germany) indicate that hopanoid producing bacteria were present in significant amounts either in the water column above the sediment or in the top layer of the sediment. Dihomohopan-32-ol is shown to be representative of the total hopanoid content of the sediment and its distribution is tentatively correlated with the eutrophication process which has occurred in Lake Constance over the past 50 years.     

Monolayer and calorimetric studies of phosphatidylcholines containing branched-chain fatty acids and of their interactions with cholesterol and with a bacterial hopanoid in model membranes

Although methyl iso- and anteiso-branched fatty acids occur widely in the membrane lipids of prokaryotic microorganisms, relatively little is known about the physical properties of phospholipids containing these fatty acids. We report here a monolayer and differential scanning calorimetric characterization of several synthetic phosphatidylcholines containing branched-chain fatty acids, and describe the interactions of these phospholipids with cholesterol and with a bacterial hopanoid. We find that monolayers as well as bilayers of methyl isobranched- and especially of methyl anteisobranched-fatty-acid-containing phosphatidylcholines exhibit a reduced solid-to-fluid phase transition temperature in comparison with linear saturated fatty acid-containing phosphatidylcholines of comparable chain length. We also find that the liquid-condensed or gel states of branched-chain fatty acid-containing phosphatidylcholines are partially disordered relative to those of phospholipids containing linear saturated fatty acids, although the presence of a methyl branch has only a small effect on hydrocarbon chain packing in the liquid-expanded or liquid-crystalline states. The presence of cholesterol was found to produce a marked condensation of liquid-expanded films and a small condensation of liquid-condensed films, whether the phosphatidylcholine contained linear or branched-chain fatty acyl constituents. The presence of a bacterial hopanoid produced similar, although slightly smaller, monolayer-condensing effects, indicating that these compounds may perform a cholesterol-like function in bacterial membranes.