Transcriptomic response of female adult moths to host and non-host plants in two closely related species

BACKGROUND

Divergent selection has been shown to promote speciation in many taxa and especially in phytophagous insects. In the Ostrinia species complex, the European corn borer (ECB) and adzuki bean borer (ABB) are two sibling species specialized to different host plants. The first is a well-known maize pest, whereas the second is a polyphagous species associated with various dicotyledons. Their specialization to host plants is driven by morphological, behavioral and physiological adaptations. In particular, previous studies have shown that ECB and ABB display marked behavior with regard to plant choice during oviposition, involving specific preference and avoidance mechanisms. In this study, our goal was to identify the mechanisms underlying this host-plant specialization in adult females through an analysis of their gene expression. We assembled and annotated a de novo reference transcriptome and measured differences in gene expression between ECB and ABB females, and between environments. We related differentially expressed genes to host preference behavior, and highlighted the functional categories involved. We also conducted a specific analysis of chemosensory genes, which are considered to be good candidates for host recognition before oviposition.

RESULTS

We recorded more differentially expressed genes in ECB than in ABB samples, and noticed that the majority of genes potentially involved in the host preference were different between the two species. At the functional level, the response to plant environment in adult females involved many processes, including the metabolism of carbohydrates, lipids, proteins, and amino acids; detoxification mechanisms and immunity; and the chemosensory repertoire (as expected). Until now, most of the olfactory receptors described in Ostrinia spp. had been tested for their putative role in pheromone recognition by males. Here we observed that one specific olfactory receptor was clearly associated with ECB's discrimination between maize and mugwort conditions, highlighting a potential new candidate involved in plant odor discrimination in adult females.

CONCLUSIONS

Our results are a first step toward the identification of candidate genes and functions involved in chemosensory processes, carbohydrate metabolism, and virus and retrovirus dynamics. These candidates provide new avenues for research into understanding the role of divergent selection between different environments in species diversification.

Genome-wide nucleotide diversity of hatchery-reared Atlantic and Mediterranean strains of brown trout Salmo trutta compared to wild Mediterranean populations

A genome-wide assessment of diversity is provided for wild Mediterranean brown trout Salmo trutta populations from headwater tributaries of the Orb River and from Atlantic and Mediterranean hatchery-reared strains that have been used for stocking. Double-digest restriction-site-associated DNA sequencing (dd-RADseq) was performed and the efficiency of de novo and reference-mapping approaches to obtain individual genotypes was compared. Large numbers of single nucleotide polymorphism (SNP) markers with similar genome-wide distributions were discovered using both approaches (196 639 v. 121 016 SNPs, respectively), with c. 80% of the loci detected de novo being also found with reference mapping, using the Atlantic salmon Salmo salar genome as a reference. Lower mapping density but larger nucleotide diversity (π) was generally observed near extremities of linkage groups, consistent with regions of residual tetrasomic inheritance observed in salmonids. Genome-wide diversity estimates revealed reduced polymorphism in hatchery strains (π = 0·0040 and π = 0·0029 in Atlantic and Mediterranean strains, respectively) compared to wild populations (π = 0·0049), a pattern that was congruent with allelic richness estimated from microsatellite markers. Finally, pronounced heterozygote deficiency was found in hatchery strains (Atlantic F_IS = 0·18; Mediterranean F_IS = 0·42), indicating that stocking practices may affect the genetic diversity in wild populations. These new genomic resources will provide important tools to define better conservation strategies in S. trutta.

Mevalonate-independent methylerythritol phosphate pathway for isoprenoid biosynthesis. Elucidation and distribution

A long-overlooked metabolic pathway for isoprenoid biosynthesis, the mevalonate-independent methylerythritol phosphate (MEP) pathway, is present in many bacteria and in the chloroplasts of all phototrophic organisms. It represents an alternative to the well known mevalonate pathway, which is present in animals, fungi, plant cytoplasm, archaebacteria, and some eubacteria. This contribution summarizes key steps of its elucidation and the state-of-the-art knowledge of this biosynthetic pathway, which represents a novel target for antibacterial and antiparasitic drugs.

Zeaxanthin and menaquinone-7 biosynthesis in Sphingobacterium multivorum via the methylerythritol phosphate pathway

Feeding of [1-(13)C]glucose, [U-(13)C(6)]glucose, [3-(13)C]alanine and [1-(13)C]acetate to Sphingobacterium multivorum showed that this bacterium utilizes the methylerythritol phosphate pathway for the biosynthesis of menaquinone-7 and zeaxanthin, a carotenoid of industrial importance. Differential incorporation of the labeled precursors gave some insight into the preferred carbon sources involved in isoprenoid biosynthesis.

Structural diversity of the triterpenic hydrocarbons from the bacterium Zymomonas mobilis: the signature of defective squalene cyclization by the squalene/hopene cyclase

Twelve polycyclic triterpenic hydrocarbons (alpha- and gamma-polypodatetraenes, dammara-20(21),24-diene, 17-isodammara-12,24-diene, eupha-7,24-diene, hop-17(21)-ene, neohop-13(18)-ene, 17-isodammara-20(21),24-diene, neohop-12-ene, fern-8-ene, diploptene and hop-21-ene) were detected in the hydrocarbon fraction from the bacterium Zymomonas mobilis. Some of them have never been reported from bacteria. These triterpenes were present in Z. mobilis in significant amounts, comparable to those of diploptene, which is usually the major triterpenic hydrocarbon in hopanoid-producing bacteria. The occurrence of such compounds confirms the lack of specificity of bacterial squalene cyclases and the possibility of alternative cyclization routes induced by the existence in the cyclization process of intermediate carbocations of sufficient lifetime.

Novel hopanoids from Frankia spp. and related soil bacteria. Squalene cyclization and significance of geological biomarkers revisited

Three series of hopanoids, differing by their configurations at C-17 and C-21, have been identified in several Frankia spp. and other related soil bacteria. The widespread bacterial hopanoids of the 17beta(H),21beta(H) series were accompanied by their isomers of the 17beta(H),21alpha(H) (moretane) and 17alpha(H), 21beta(H) series. The latter series has not previously been found in living organisms and is considered to be a result of the abiotic isomerization of the thermodynamically less stable 17beta(H),21beta(H) hopanoids. This simultaneous presence of three isomeric hopanoid series highlights intriguing problems in the biogenesis of the bacteriohopane skeleton and partly questions the significance of hopanic biomarkers in sediments.

Cutting edge: human gamma delta T cells are activated by intermediates of the 2-C-methyl-D-erythritol 4-phosphate pathway of isoprenoid biosynthesis

Activation of V gamma 9/V delta 2 T cells by small nonprotein Ags is frequently observed after infection with various viruses, bacteria, and eukaryotic parasites. We suggested earlier that compounds synthesized by the 2-C:-methyl-D-erythritol 4-phosphate (MEP) pathway of isopentenyl pyrophosphate synthesis are responsible for the V gamma 9/V delta 2 T cell reactivity of many pathogens. Using genetically engineered Escherichia coli knockout strains, we now demonstrate that the ability of E. coli extracts to stimulate gamma delta T cell proliferation is abrogated when genes coding for essential enzymes of the MEP pathway, dxr or gcpE, are disrupted or deleted from the bacterial genome.

Novel methylated triterpenoids of the gammacerane series from the nitrogen-fixing bacterium Bradyrhizobium japonicum USDA 110

The nitrogen-fixing, symbiotic root-nodule forming bacterium Bradyrhizobium japonicum USDA 110 contained gammacerane derivatives next to triterpenoids of the hopane series. Diploptene, diplopterol, 2 beta-methyldiplopterol, aminobacteriohopanetriol and adenosylhopane were accompanied by tetrahymanol and the corresponding novel methylated homologues 2 beta-methyltetrahymanol, 20 alpha-methyltetrahymanol, and 2 beta,20 alpha-dimethyltetrahymanol. Incorporation of [(2)H(3)]methyl-L-methionine indicated that the additional methyl groups originated from methionine, probably with S-adenosylmethionine acting as methyl donor, with retention of the three deuterium atoms. The simultaneous presence of hopane and gammacerane derivatives seems a characteristic feature of the genus Bradyrhizobium and the phylogenetically closely related Rhodopseudomonas palustris.

Identification of gcpE as a novel gene of the 2-C-methyl-D-erythritol 4-phosphate pathway for isoprenoid biosynthesis in Escherichia coli

The 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway for isoprenoid biosynthesis is essential in most eubacteria and plants and has remarkable biotechnological interest. However, only the first steps of this pathway have been determined. Using bioinformatic and genetic approaches, we have identified gcpE as a novel gene of the MEP pathway. The distribution of this gene in bacteria and plants strictly parallels that of the gene encoding 1-deoxy-D-xylulose 5-phosphate reductoisomerase, which catalyses the first committed step of the MEP pathway. Our data demonstrate that the gcpE gene is essential for the MEP pathway in Escherichia coli and indicate that this gene is required for the trunk line of the isoprenoid biosynthetic route.

Genetic evidence of branching in the isoprenoid pathway for the production of isopentenyl diphosphate and dimethylallyl diphosphate in Escherichia coli

An alternative mevalonate-independent pathway for isoprenoid biosynthesis has been recently discovered in eubacteria (including Escherichia coli) and plant plastids, although it is not fully elucidated yet. In this work, E. coli cells were engineered to utilize exogenously provided mevalonate and used to demonstrate by a genetic approach that branching of the endogenous pathway results in separate synthesis of the isoprenoid building units isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP). In addition, the IPP isomerase encoded by the idi gene was shown to be functional in vivo and to represent the only possibility for interconverting IPP and DMAPP in this bacterium.

Deuterium-labelled isotopomers of 2-C-methyl-D-erythritol as tools for the elucidation of the 2-C-methyl-D-erythritol 4-phosphate pathway for isoprenoid biosynthesis

Escherichia coli synthesizes its isoprenoids via the mevalonate-independent 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. The MC4100dxs::CAT strain, defective in deoxyxylulose-5-phosphate synthase, which is the first enzyme in this metabolic route, exclusively synthesizes its isoprenoids from exogenous 2-C-methyl-D-erythritol (ME) added to the culture medium. The fate of the hydrogen atoms in the MEP pathway was followed by the incorporation of [1,1-(2)H(2)]ME and [3,5,5,5-(2)H(4)]ME. The two C-1 hydrogen atoms of ME were found without any loss in the prenyl chain of menaquinone and/or ubiquinone on the carbon atoms derived from C-4 of isopentenyl diphosphate (IPP) and on the E-methyl group of dimethylallyl diphosphate (DMAPP), the C-5 hydrogen atoms on the methyl groups derived from IPP C-5 methyl group and the Z-methyl group of DMAPP. This showed that no changes in the oxidation state of these carbon atoms occurred in the reaction sequence between MEP and IPP. Furthermore, no deuterium scrambling was observed between the carbon atoms derived from C-4 and C-5 of IPP or DMAPP, suggesting a completely stereoselective IPP isomerase or no significant activity of this enzyme. The C-3 deuterium atom of [3,5,5,5-(2)H(4)]ME was preserved only in the DMAPP starter unit and was completely missing from all those derived from IPP. This finding, aided by the non-essential role of the IPP isomerase gene, suggests the presence in E. coli of two different routes towards IPP and DMAPP, starting from a common intermediate derived from MEP.

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.

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.

CO2 as main carbon source for isoprenoid biosynthesis via the mevalonate-independent methylerythritol 4-phosphate route in the marine diatoms Phaeodactylum tricornutum and Nitzschia ovalis

Isoprenoid biosynthesis was investigated in the two diatoms Phaeodactylum tricornutum and Nitzschia ovalis by labeling experiments performed in mixotrophic growth conditions with sodium [1-(13)C]acetate, 13CO2, [1-(13)C]glucose, sodium [3-(13)C]pyruvate and 1-deoxy-D-[5,5-(2)H2]xylulose. A clear dichotomy was found. Acetate was the preferred carbon source for the formation of the sterols in the cytoplasm via the mevalonate pathway. Carbon dioxide was the main source for phytol biosynthesis in the chloroplasts via the mevalonate-independent methylerythritol 4-phosphate pathway. The two diatoms showed the same compartmentation for isoprenoid biosynthesis as that previously found in higher plants, the red alga Porphyridium cruentum and the Chrysophyte Ochromonas danica.

On the absence of the glyceraldehyde 3-phosphate/pyruvate pathway for isoprenoid biosynthesis in fungi and yeasts

The biosynthesis of isopentenyl diphosphate, the central intermediate of isoprenoid formation, was investigated in the fungus Aschersonia aleyrodis and the yeast Rhodotorula glutinis. The incorporation of 13C-labeled glucose or acetate into their isoprenoids showed that ergosterol in both micro-organisms, ubiquinone in R. glutinis and dihydro-ubiquinone, beta-carotene and triterpenes of the hopane series in A. aleyrodis were synthesized via the mevalonate pathway. No evidence for the presence of the alternative mevalonate-independent glyceraldehyde 3-phosphate/pyruvate pathway was found.

Isoprenoid biosynthesis via the mevalonate-independent route, a novel target for antibacterial drugs?

Mevalonate was accepted as the universal precursor of all isoprenoids. This assertion was however revealed to be partially incorrect. Incorporation of 13C labeled acetate and glucose into bacterial triterpenoids of the hopane series allowed for the discovery and the partial elucidation of a novel biosynthetic pathway leading to isopentenyl diphosphate. The C5 skeleton of isoprenic units results from the condensation of (hydroxyethyl)thiamin on the carbonyl group of glyceraldehyde 3-phosphate, yielding D-1-deoxyxylulose 1-phosphate. A subsequent intramolecular rearrangement is involved in the formation of the branched isoprenic skeleton. 2C-Methyl-D-erythritol (or its mono- or diphosphate) was shown to be a putative intermediate. This pathway is widespread in bacteria including opportunistic pathogens or innocuous species related to well-known pathogens. In plants, it is involved in the formation of essential chloroplast isoprenoids (carotenoids, phytol, plastoquinone) and of probably most other plastid related isoprenoids of more restricted distribution (isoprene, mono- and diterpenoids). Therefore it potentially represents a novel target for antibacterial drugs and herbicides.

Distribution of the mevalonate and glyceraldehyde phosphate/pyruvate pathways for isoprenoid biosynthesis in unicellular algae and the cyanobacterium Synechocystis PCC 6714

Isopentenyl diphosphate, the universal isoprenoid precursor, can be produced by two different biosynthetic routes: either via the acetate/mevalonate (MVA) pathway, or via the more recently identified MVA-independent glyceraldehyde phosphate/pyruvate pathway. These two pathways are easily differentiated by incorporation of [1-13C]glucose and analysis of the resulting labelling patterns found in the isoprenoids. This method was successfully applied to several unicellular algae raised under heterotrophic growth conditions and allowed for the identification of the pathways that were utilized for isoprenoid biosynthesis. All isoprenoids examined (sterols, phytol, carotenoids) of the green algae Chlorella fusca and Chlamydomonas reinhardtii were synthesized via the GAP/pyruvate pathway, as in another previously investigated green alga, Scenedesmus obliquus, which was also shown in this study to synthesize ubiquinone by the same MVA-independent route. In the red alga Cyanidium caldarium and in the Chrysophyte Ochromonas danica a clear dichotomy was observed: as in higher plants, sterols were formed via the MVA route, whereas chloroplast isoprenoids (phytol in Cy. caldarium and O. danica and beta-carotene in O. danica) were synthesized via the GAP/pyruvate route. In contrast, the Euglenophyte Euglena gracilis synthesized ergosterol, as well as phytol, via the acetate/MVA route. Similar feeding experiments were performed with the cyanobacterium Synechocystis PCC 6714 using [1-13C]- and [6-13C]-glucose. The two isoprenoids examined, phytol and beta-carotene, were shown to have the typical labelling pattern derived from the GAP/pyruvate route.

Distribution of mevalonate and glyceraldehyde 3-phosphate/pyruvate routes for isoprenoid biosynthesis in some gram-negative bacteria and mycobacteria

Labeling experiments using [1-13C]acetate or [1-13C]glucose were performed with opportunistic pathogenic bacteria, with innocuous bacteria related to pathogenic species or with phytopathogenic species. The labeling pattern was determined in the isoprenic moiety of ubiquinone or menaquinone derivatives. These experiments showed that Acinetobacter, Citrobacter, Erwinia, Pseudomonas, Burkholderia, Ralstonia and Mycobacterium synthesize their isoprenoids via the mevalonate-independent glyceraldehyde 3-phosphate/pyruvate route. Enzymes of this novel bacterial metabolic route, which is apparently absent in vertebrates and man, therefore represent potential targets for a novel type of antibacterial drugs.

Mevalonate-derived isopentenyl diphosphate is the biosynthetic precursor of ubiquinone prenyl side chain in tobacco BY-2 cells

Study of the incorporation of 13C-labelled glucose or pyruvate into the isoprenoids of tobacco BY-2 cells allowed the biosynthetic origin of isopentenyl diphosphate to be determined. Sterols synthesized in the cytoplasm and the prenyl chain of ubiquinone Q10 located in mitochondria were derived from the same isopentenyl diphosphate pool, synthesized from acetyl-CoA through mevalonate, whereas the prenyl chain of plastoquinone was obtained from the mevalonate-independent glyceraldehyde 3-phosphate/pyruvate route, like all chloroplast isoprenoids from higher plants. These results are in accord with the compartmentation and complete enzymic independence of the biosynthesis of long-chain all-trans polyprenols in mitochondria and chloroplasts.

Cloning and characterization of a gene from Escherichia coli encoding a transketolase-like enzyme that catalyzes the synthesis of D-1-deoxyxylulose 5-phosphate, a common precursor for isoprenoid, thiamin, and pyridoxol biosynthesis

For many years it was accepted that isopentenyl diphosphate, the common precursor of all isoprenoids, was synthesized through the well known acetate/mevalonate pathway. However, recent studies have shown that some bacteria, including Escherichia coli, use a mevalonate-independent pathway for the synthesis of isopentenyl diphosphate. The occurrence of this alternative pathway has also been reported in green algae and higher plants. The first reaction of this pathway consists of the condensation of (hydroxyethyl)thiamin derived from pyruvate with the C1 aldehyde group of D-glyceraldehyde 3-phosphate to yield D-1-deoxyxylulose 5-phosphate. In E. coli, D-1-deoxyxylulose 5-phosphate is also a precursor for the biosynthesis of thiamin and pyridoxol. Here we report the molecular cloning and characterization of a gene from E. coli, designated dxs, that encodes D-1-deoxyxylulose-5-phosphate synthase. The dxs gene was identified as part of an operon that also contains ispA, the gene that encodes farnesyl-diphosphate synthase. D-1-Deoxyxylulose-5-phosphate synthase belongs to a family of transketolase-like proteins that are highly conserved in evolution.

Biosynthesis of isoprenoids in higher plant chloroplasts proceeds via a mevalonate-independent pathway

Isopentenyl diphosphate (IPP) is the biological C5 precursor of isoprenoids. By labeling experiments using [1-(13)C]glucose, higher plants were shown to possess two distinct biosynthetic routes for IPP biosynthesis: while the cytoplasmic sterols were formed via the acetate/mevalonate pathway, the chloroplast-bound isoprenoids (beta-carotene, lutein, prenyl chains of chlorophylls and plastoquinone-9) were synthesized via a novel IPP biosynthesis pathway (glyceraldehyde phosphate/pyruvate pathway) which was first found in eubacteria and a green alga. The dichotomy in isoprenoid biosynthesis in higher plants allows a reasonable interpretation of previous odd and inconclusive results concerning the biosynthesis of chloroplast isoprenoids, which so far had mainly been interpreted in the frame of models using compartmentation of the mevalonate pathway.

Bacterial triterpenoids of the hopane series from the prochlorophyte Prochlorothrix hollandica and their intracellular localization

35-O-beta-Galacturonopyranosyl-, 35-O-beta-3,5-anhydro-galacturonopyranosyl- and 35-O-alpha-altruronopyranosylbacteriohopanetetrol accompanied by their 2 beta-methyl homologues have been isolated from Prochlorothrix hollandica. We report here C35 triterpenoids of the hopane series in a prochlorophyte, a group of prokaryotic oxigenic phototrophs of the cyanobacterial lineage. Like many cyanobacteria, P. hollandica contains a mixture of non-methylated as well as 2 beta-methylhopanoids. After side-chain cleavage by periodic acid oxidation followed by sodium borohydride reduction, these hopanoids could be localized in cell walls and thylakoids, in accordance with their role as membrane stabilizers.

Biosynthesis of isoprenoids (carotenoids, sterols, prenyl side-chains of chlorophylls and plastoquinone) via a novel pyruvate/glyceraldehyde 3-phosphate non-mevalonate pathway in the green alga Scenedesmus obliquus

Isoprenoid biosynthesis was investigated in the green alga Scenedesmus obliquus grown heterotrophically on 13C-labelled glucose and acetate. Several isoprenoid compounds were isolated and investigated by 13C-NMR spectroscopy. According to the 13C-labelling pattern indicated by the 13C-NMR spectra, the biosynthesis of all plastidic isoprenoids investigated (prenyl side-chains of chlorophylls and plastoquinone-9, and the carotenoids beta-carotene and lutein), as well as of the non-plastidic cytoplasmic sterols, does not proceed via the classical acetate/mevalonate pathway (which leads from acetyl-CoA via mevalonate to isopentenyl diphosphate), but via the novel glyceraldehyde 3-phosphate/pyruvate route recently detected in eubacteria. Formation of isopentenyl diphosphate involves the condensation of a C2 unit derived from pyruvate decarboxylation with glyceraldehyde 3-phosphate and a transposition yielding the branched C5 skeleton of isoprenic units.

Structure elucidation and biosynthesis of 31-methylhopanoids from Acetobacter europaeus. Studies on a new series of bacterial triterpenoids

Apart from a mixture of bacteriohopanetetrols already found in other Acetobacter species, four new 3 beta-methylhopanoids have been isolated from Acetobacter europaeus. All of them present an ether linkage between a bacteriohopanetetrol or a bacteriohopanepentol and a carbapseudopentose moiety often found in bacterial hopanoids. Three of these ethers were shown by comparison with synthetic reference hopanoids to posess a supplementary methyl group at C31. This novel series of methylhopanoids may be the precursor of yet unidentified molecular fossils found in sediments. [methyl-2H3]Methionine was efficiently incorporated into the 31-methylhopanoids with retention of all three deuterium atoms in the transferred methyl group. This labelling pattern might be consistent with a rather rarely found methylation reaction of an enol.

Isoprenoid biosynthesis in bacteria: a novel pathway for the early steps leading to isopentenyl diphosphate

Incorporation of 13C-labelled glucose, acetate, pyruvate or erythrose allowed the determination of the origin of the carbon atoms of triterpenoids of the hopane series and/or of the ubiquinones from several bacteria (Zymomonas mobilis, Methylobacterium fujisawaense, Escherichia coli and Alicyclobacillus acidoterrestris) confirmed our earlier results obtained by incorporation of 13C-labelled acetate into the hopanoids of other bacteria and led to the identification of a novel biosynthetic route for the early steps of isoprenoid biosynthesis. The C5 framework of isoprenic units results most probably (i) from the condensation of a C2 unit derived from pyruvate decarboxylation (e.g. thiamine-activated acetaldehyde) on the C-2 carbonyl group of a triose phosphate derivative issued probably from dihydroxyacetone phosphate and not from pyruvate and (ii) from a transposition step. Although this hypothetical biosynthetic pathway resembles that of L-valine biosynthesis, this amino acid or its C5 precursors could be excluded as intermediates in the formation of isoprenic units.

Prokaryotic triterpenoids: O-alpha-D-glucuronopyranosyl bacteriohopanetetrol, a novel hopanoid from the bacterium Rhodospirillum rubrum

A novel hopanoid bearing a glucuronopyranosyl residue linked via an alpha-glycosidic bond to the hydroxyl group of C-35 in bacteriohopanetetrol was isolated, from the type strain of Rhodospirillum rubrum as well as from a mutant lacking blue carotenoid.

Localization and distribution of hopanoids in membrane systems of the cyanobacterium Synechocystis PCC 6714

Intracellular localization of triterpenic membrane stabilizers of the hopane series is described for the first time for a cyanobacterium. In Synechocystis PCC 6714, a bacteriohopanetetrol derivative (main compound) and diplopterol were detected in cell wall (CW) and thylakoid membrane (TM). Both hopanoids were enriched 4.5-fold and 9.0-fold in CW and outer membrane (OM) fractions, respectively, compared to TMs.

Prokaryotic triterpenoids. A novel hopanoid from the ethanol-producing bacterium Zymomonas mobilis

Among the triterpenoids of the bacterium Zymomonas mobilis a novel hopanoid, 32-oxobacteriohopane-33,34,35-triol beta-linked via its primary hydroxy group to glucosamine, has been isolated as a minor compound.

Prokaryotic hopanoids: the biosynthesis of the bacteriohopane skeleton. Formation of isoprenic units from two distinct acetate pools and a novel type of carbon/carbon linkage between a triterpene and D-ribose

Incorporation of 13C-labelled acetate into the hopanoids of the purple non-sulfur bacteria Rhodopseudomonas palustris and Rhodopseudomonas acidophila and the facultative methylotroph Methylobacterium organophilum showed that the bacteriohopane skeleton is built from an unique carbon/carbon linkage between the triterpenic hopane moiety and the C-5 carbon of a D-ribose derivative arising from the non-oxidative pentose phosphate pathway. Furthermore a probable compartmentation of the acetate metabolism could be observed in these bacteria. Whereas exogenous acetate was directly incorporated into the glucose derivatives and poly-(3-hydroxybutyrate), the isoprenic units were apparently solely synthesized from two acetate units arising from the glyoxylate cycle and a third one issued either from the glyoxylate cycle or from the Entner-Doudoroff pathway of glucose catabolism. Although an unknown biosynthetic pathway different from that usually proposed for isoprenoid biosynthesis can not be excluded, the former hypothesis explained all labelling patterns observed on the triterpenic skeleton.

Polyterpenoids as cholesterol and tetrahymanol surrogates in the ciliate Tetrahymena pyriformis

The tetracyclic sterol precursors, cyclolaudenol, cycloartenol and lanosterol, inhibit efficiently the tetrahymanol biosynthesis in the ciliate Tetrahymena pyriformis, as reported earlier for cholesterol and other sterols. The prokaryotic bacteriohopanetetrols have little effect, and diplopterol, another hopanoid, as well as the carotenoid, canthaxanthin, have no effect. In the presence of triparanol, a hypocholesterolemic drug inhibiting the squalene cyclase of T. pyriformis and modifying the fatty acid metabolism, the cells do not grow further, but growth can be restored by the addition to the culture medium of suitable polyterpenoids. Thus, growth in presence of triparanol (13 microM) is almost normal after addition of a sterol such as sitosterol and cyclolaudenol, and longer lag times and lower absorbances than those of untreated cultures are observed in presence of cyclartenol, lanosterol, euphenol (a lanosterol isomer), bacteriohopanetetrols and three carotenoids. No growth at all is observed in the presence of tetrahymanol and diplopterol, although these triterpenoids are the normal reinforcers of the ciliate, probably because of a poor bioavailability. Thus, structurally different polyterpenoids are (at least partially) functionally equivalent and capable of replacing tetrahymanol or sterols and might act as membrane reinforcers in T. pyriformis cells.

The hopanoids of the purple non-sulfur bacteria Rhodopseudomonas palustris and Rhodopseudomonas acidophila and the absolute configuration of bacteriohopanetetrol

Five complex hopanoids have been detected in the purple non-sulfur bacterium Rhodopseudomonas acidophila. Next to the polyfunctionalized methylcyclopentane bacteriohopanetetrol ether already isolated from Methylobacterium organophilum, 35-carbamoylbacteriohopane-32,33,34-triol, 34,35-dicarbamoylbacteriohopane-32,33-diol and two nucleoside analogues, (22R)-30-(5'-adenosyl)hopane and (22S)-30-(5'-adenosyl)hopane were isolated and identified by spectroscopic and chemical methods. In Rhodopseudomonas palustris, however, only 35-amino-bacteriohopane-32,33,34-triol was detected. Chemical correlation between adenosylhopane and bacteriohopanetetrol, as well as comparison of derivatives obtained from bacterial and synthetic hopanoids, permitted the determination of the configurations of all asymmetric centres of the side-chain of bacteriohopanetetrol as 22R, 32R, 33R and 34S. According to the stereochemistry, this side-chain could be a D-ribose derivative linked through its C-5 carbon atom to the hopane skeleton.

The action of the systemic fungicides tridemorph and fenpropimorph on sterol biosynthesis by the soil amoeba Acanthamoeba polyphaga

Tridemorph and fenpropimorph, two systemic fungicides known by their inhibitory effects on sterol biosynthesis in fungi and plants, were administered in vivo to the amoeba Acanthamoeba polyphaga. The compounds did not kill the cells, but modified completely their sterol pattern. Fungicide-exposed cells accumulated cyclopropylsterols indicating a partial blockage of the cyclopropane isomerase as in higher plants and delta 8-sterols indicating an inhibition of the delta 8----delta 7 isomerase as in fungi. Three new sterols, 4 alpha-methylergosta-9(11),24(28)-dienol, ergosta-6,8,22-trienol and poriferasta-6,8,22-trienol were isolated and identified, the former from control cells, the two latter from fungicide-treated cells. These results are in accordance with our previous results on the presence of cycloartenol as sterol precursor and confirm our hypothesis on a phylogenetic relationship of Acanthamoeba polyphaga with photosynthetic phyla.

Sterol biosynthesis via cycloartenol and other biochemical features related to photosynthetic phyla in the amoeba Naegleria lovaniensis and Naegleria gruberi

The sterols and sterol precursors of two amoebae of the genus Naegleria, Naegleria lovaniensis and Naegleria gruberi were investigated. Cycloartenol, the sterol precursor in photosynthetic organisms, is present in both amoebae. In N. lovaniesis, it is accompanied by lanosterol and parkeol, as well as by the 24,25-dihydro derivatives of these triterpenes. One of the most striking features of these amoebae is the accumulation of 4 alpha-methylsterols which are present in similar amounts as those of 4,4-desmethylsterols (3-5 mg/g, dry weight). 4 alpha-Methylergosta-7,22-dienol was identified as a new compound. Ergosterol was the major 4,4-desmethylsterol, accompanied by small amounts of C27 and other C28 sterols. Treatment of N. lovaniensis with fenpropimorph modified the sterol pattern of this amoeba and inhibited its growth. This fungicide, known to inhibit steps of sterol biosynthesis in fungi and plants, induced the disappearance of 4 alpha-methyl-delta 7-sterols and the appearance of the unusual delta 6,8,22-ergostatrienol as in A. polyphaga. These results might be explained by a partial inhibition of the delta 8----delta 7 isomerase, the small amounts of delta 7-sterols formed being converted into ergosterol which is still present in fenpropimorph-exposed cells. De novo sterol biosynthesis in N. lovaniensis was shown by incorporation of [1-14C]acetate into sterols and sterol precursors, especially cycloartenol. Lanosterol and parkeol were not significantly labelled. Furthermore, [3-3H]squalene epoxide was efficiently cyclized by a cell-free system of this amoeba into cycloartenol, and again no significant radioactivity was detected in lanosterol and parkeol. This shows that cycloartenol, the sterol precursor in plants and algae, is also the sterol precursor in Naegleria species, and that these amoebae, like A. polyphaga, are related by some biosynthetic pathways to photosynthetic phyla. Lanosterol, the sterol precursor in non-photosynthetic phyla (animal and fungi) and parkeol are more likely dead-ends of this biosynthetic pathway. The peculiar phylogenetic position of these protozoa was further emphasized by the action of indole acetic acid and other auxine-like compounds on their growth. Indeed amoebic growth was enhanced in the presence of these higher plant growth hormones. The differences in the sterol composition of the protozoa we have hitherto examined is related to their sensitivity toward polyene macrolide antibiotics.(ABSTRACT TRUNCATED AT 400 WORDS)

Microbial lipids betrayed by their fossils

Novel families of microbial lipids have been betrayed by their molecular fossils. They comprise the very widespread and varied hopanoids, and 'orphan' lipids. Membrane reinforcement appears to be universally achieved by these polyterpenoids; a hypothetical phylogenetic tree comprises the above, some postulated intermediates, bacterial carotenoids, cycloartenol, and finally cholesterol.

Enzymatic cyclization of all-trans pentaprenyl and hexaprenyl methyl ethers by a cell-free system from the protozoon Tetrahymena pyriformis. The biosynthesis of scalarane and polycyclohexaprenyl derivatives

A cell-free system from the protozoon Tetrahymena pyriformis capable of cyclizing squalene into tetrahymanol cyclizes all-trans pentaprenyl methyl ether to a scalarane-type sesterterpene and all-trans hexaprenyl methyl ether to bicyclo-, tricyclo-, tetracyclo- and pentacyclohexaprenyl methyl ethers, each corresponding to a possible cationic intermediate. The structures of the cyclization products have been determined by spectroscopic methods and are compatible with a biogenetic scheme involving polyprenyl ether cyclization. This is the first direct proof of an enzymatic cyclization of higher isoprenic alcohol derivatives, and we assume it was performed by the squalene-to-hopane cyclase of the protozoon. The formation of a scalarane-type sesterterpene from C25 polyprenyl methyl ether suggests that these terpenoids, whose presence is restricted to a few sponges, might be in fact microbial metabolites. Tricyclopolyprenyl derivatives have been identified in the organic matter from numerous sediments and they were interpreted as being chemical fossils of still unidentified microorganisms. The cyclization of hexaprenyl methyl ether is the first attempt of identification of these tricyclopolyprenol derivatives in living organisms.

Sterol biosynthesis de nova via cycloartenol by the soil amoeba Acanthamoeba polyphaga

The soil amoeba Acanthamoeba polyphaga is capable of synthesizing its sterols de novo from acetate. The major sterols are ergosterol and poriferasta-5,7,22-trienol. Furthermore C28 and C29 sterols of still unknown structure with an aromatic B-ring are also synthesized by the amoeba. The first cyclic sterol precursor is cycloartenol, which is the sterol precursor in all photosynthetic phyla. No trace of lanosterol, which is the sterol precursor in animals and fungi, could be detected. These results show that at least some of the biochemical processes of Acanthamoeba polyphaga might be phylogenetically related to those of unicellular algae. Addition of exogenous sterols to the culture medium does not influence the sterol biosynthesis and the sterol composition of the cells.

Novel hopanoids from the methylotrophic bacteria Methylococcus capsulatus and Methylomonas methanica. (22S)-35-aminobacteriohopane-30,31,32,33,34-pentol and (22S)-35-amino-3 beta-methylbacteriohopane-30,31,32,33,34-pentol

The major hopanoid of the methylotrophic bacteria Methylococcus capsulatus and Methylomonas methanica was identified by spectroscopic methods as (22S)-35-aminobacteriohopane-30,31,32,33,34-pentol. Minor companions were, in both bacteria, 35-aminobacteriohopane-31,32,33,34-tetrol and in Methylomonas methanica, 35-aminobacteriohopane-32,33,34-triol. In Methylococcus capsulatus the aminopentol and the aminotetrol were accompanied by their homologues possessing an extra methyl group at C-3. Bacterial hopanoids with a functionalized C-30 carbon atom such as these two new aminopentols are possible precursors of widespread C29 hopanoid chemical fossils.

Prokaryotic triterpenoids. New bacteriohopanetetrol cyclitol ethers from the methylotrophic bacterium Methylobacterium organophilum

Together with bacteriohopanetetrol, which is identical to bacteriohopanetetrol isolated from Bacillus acidocaldarius, three other bacteriohopane derivatives were isolated from the methylotrophic bacterium Methylobacterium organophilum. Three different kinds of polar moieties were found linked to the C-35 hydroxyl group of bacteriohopanetetrol: glucosamine linked through a glycosidic bond and two new polyhydroxylated methylcyclopentanoids differing one from each other by the presence of an amino or a guanidino group and linked through an ether bond. The significance of the presence of these compounds in terms of membrane reinforcement and DNA/triterpenoid interactions is discussed.

Prokaryotic triterpenoids. 2. 2 beta-Methylhopanoids from Methylobacterium organophilum and Nostoc muscorum, a new series of prokaryotic triterpenoids

2 beta-Methylhopanoids, a new series of triterpenoids was identified from two prokaryotes. 2 beta-Methyldiplopterol was isolated from the methylotrophic bacterium Methylobacterium organophilum, and three different 2 beta-methylbacteriohopanepolyols from the cyanobacterium Nostoc muscorum. The structures of these compounds was deduced by direct comparison with 2 beta-methyldiplopterol synthesized from 22-hydroxyhopan-3-one.

Prokaryotic triterpenoids. 1. 3 beta-Methylhopanoids from Acetobacter species and Methylococcus capsulatus

3 beta-Methylbacteriohopanepolyol derivatives were isolated from three bacteria, Acetobacter pasteurianus ssp. pasteurianus, Methylococcus capsulatus and Nostoc muscorum, and identified by spectroscopic methods and direct comparison with 3 beta-methyldiplopterol and 3 beta-methylhopan-29-ol synthesized from 22-hydroxyhopan-3-one. The 3 beta-methylhopanoid content of A. pasteurianus ssp. pasteurianus could be dramatically increased (up to 60% of the total hopanoid content) by addition of L-methionine, the actual methyl donor, to the culture medium.

Prokaryotic triterpenoids. 3. The biosynthesis of 2 beta-methylhopanoids and 3 beta-methylhopanoids of Methylobacterium organophilum and Acetobacter pasteurianus ssp. pasteurianus

The incorporation of L-[methyl-3H,14C]methionine or L-(methyl-2H3)methionine into 2 beta-methyldiplopterol of Methylobacterium organophilum and various 3 beta-methylhopanoids of Acetobacter pasteurianus ssp. pasteurianus showed that all three hydrogen atoms of the transferred methyl group are retained in the triterpenoids. These methylations are compatible with a methylation substrate such as a delta 2-hopanoid in the case of the 2 beta-methylhopanoid biosynthesis and of a delta 2-hopanoid or squalene in the case of the formation of 3 beta-methylhopanoids. The intervention of intermediates possessing an exomethylene group or a cyclopropane ring is excluded.