Comparative phytochemical analysis of four Mexican Nymphaea species

Four Mexican Nymphaea species, N. ampla, N. pulchella, N. gracilis and N. elegans belonging to subgenera Brachyceras were analyzed. In this work two 5-glycosyl isoflavones, 7,3',4'-trihydroxy-5-O-beta-D-(2''-acetyl)-xylopyranosylisoflavone (1) and 7,3',4'-trihydroxy-5-O-alpha-L-rhamnopyranosylisoflavone (2), were isolated from N. ampla and N. pulchella, respectively, together with other known 3-glycosyl flavones and triterpene saponins from the same four species. The structures were elucidated by 1D and 2D NMR, FABMS, and other spectroscopic analyses. These results confirmed that the four species were different from each other and established that N. pulchella represents a different taxa than N. ampla. In addition, the 5-glycosyl isoflavones could be considered as a taxonomic character of this group of plants.

Identification and functional analysis of dTDP-glucose-4,6-dehydratase gene and its linked gene cluster in an aminoglycoside antibiotics producer of Streptomyces tenebrarius H6

Streptomyces tenebrarius H6 produces a variety of aminoglycoside antibiotics, such as apramycin, tobramycin, and kanamycin B. Primers were designed according to the highly conserved sequences of the dTDP-glucose-4,6-dehydratase genes, and a 0.6-kb PCR product was obtained from S. tenebrarius H6 genomic DNA. With the 0.6-kb PCR product as a probe, a BamHI 7.0-kb fragment was isolated. DNA sequence analysis of the 7.0-kb fragment revealed four ORFs and an incomplete ORF. In search of databases, the deduced product of one ORF (orfE) showed 62% identity to the dTDP-glucose-4,6-dehydratase, StrE of S. griseus. Three other ORFs (orfG1, orfG2, and orfGM) showed 55%, 62%, and 42% similarities, respectively, to glycosyltransferase from Clostridium acetobutylicum and mannosyltransferase from Xanthomonas axonopodis pv. citri str. 306 and glycosyltransferase from Pseudomonas putida KT2440. Upstream of the orfE was an incomplete ORF, and the deduced product showed 56% similarity to dTDP-4-dehydrorhamnose, StrL from S. griseus. The function of the orfE gene was studied by targeted gene disruption. The resulting mutant failed to produce tobramycin and kanamycin B, but still produced apramycin, suggesting that the orfE gene and linked gene cluster are essential for the biosynthesis of tobramycin and kanamycin B in S. tenebrarius H6.

Antineoplastic Agents. 510. Isolation and structure of dolastatin 19 from the Gulf of California sea hare Dolabella auricularia

The Gulf of California shell-less mollusc Dolabella auricularia has been found to contain a new 14-membered macrocyclic lactone linked to a 2,4-di-O-methyl-l-alpha-rhamnopyranoside, designated dolastatin 19 (1). The new cancer cell growth inhibitor (1, 8.33 x 10(-8)% yield) was obtained by bioassay (P388 lymphocytic leukemia and human cancer cell lines) directed isolation, accompanied by debromoaplysiatoxin (9.17 x 10(-7)% yield) and anhydrodebromoaplysiatoxin (2.0 x 10(-7)% yield). The structures were determined on the basis of analyses of high-resolution mass spectra and high-field NMR data. All the relative stereochemistry for the chiral centers was designated by utilizing NMR techniques.

[A new lignan glycoside from the flower of Castanea mollissima Blume]

AIM

To study the bioactive constituents of the flower of Castanea mollissima Blume.

METHODS

Compounds were isolated and purified by column chromatography of silica gel and TLC. Structures were determined by various spectroscopic data, including IR, 1HNMR and 13CNMR, EIMS, FABMS and HMBC as well as comparison of the data with those reported in literatures.

RESULTS

Five compounds were isolated and elucidated as myricetin (I), quercetin (II), gallic acid (III), 4-quinolinone-2-caboxylic acid (IV), (+) -isolariciresinol-9'-O-alpha-L-rhamnoside (V).

CONCLUSION

These compounds were separated from the flower for the first time and compound V is a new compounds, named chestnutlignansoide.

Effect of electrolytes on the surface behavior of rhamnolipids R1 and R2

The surface behavior of solutions of the rhamnolipids, R1 and R2, were investigated in the absence and presence of an electrolyte (NaCl) through surface tension measurements and optical microscopy at pH 6.8. The NaCl concentrations studied are 0.05, 0.5 and 1M. Electrolytes directly affect the carboxylate groups of the rhamnolipids. The solution/air interface has a net negative charge due to the dissociated carboxylate ions at pH 6.8 with strong repulsive electrostatic forces between the rhamnolipid molecules. This negative charge is shielded by the Na(+) ions in the electrical double layer in the presence of NaCl, causing the formation of a close-packed monolayer, and a decrease in CMC, and surface tension values. The maximum compaction is observed at 0.5M NaCl concentrations for R1 and R2 monolayers, with the R1 monolayer more compact than R2. The larger spaces left below the hydrophobic tails of R1 with respect to that of R2, due to the missing second rhamnosyl groups are thought to be responsible for the higher compaction. The rigidity of both R1 and R2 monolayers increases with the electrolyte concentration. The rigidity of the R1 monolayer is greater than that of R2 at all NaCl concentrations due to the lower hydrophilic character of R1. The variation of CMC values as a function of NaCl concentration obtained from the surface tension measurements and critical packing parameter (CPP) calculations show that spherical micelles, bilayer and rod like micelles are formed in the rhamnolipid solutions as a function of the NaCl concentration. The results of optical microscopy supported these aggregation states indicating lamellar nematic liquid crystal, cubic lamellar and hexagonal liquid crystal phases in R1 and R2 solutions depending on the NaCl concentration.

Isolation of flavonol rhamnosides fromloranthus tanakae and cytotoxic effect of them on human tumor cell lines

Loranthus tanakae Fr. et Sav. (Loranthaceae) is a species of mistletoe, a semiparasitic plant growing on the branches of Quercus and Betula species as host trees. In our ongoing search for bioactive compounds from endemic species in Korea, we have investigated to isolate the chemical constituents responsible for the antitumor effect of the MeOH extract of L. tanakae. The ethylacetate soluble part of the MeOH extract demonstrated a marginal inhibition on the proliferation of the tumor cell lines such as A549 (non small cell lung), SK-OV-3 (ovary), SK-MEL-2 (melanoma), XF498 (central nerve system), and HCT-15 (colon) in vitro. Thus, the activity-guided isolation procedure upon the ethylacetate soluble part of the extract has been carried out and finally four flavonoid rhamnopyranosides (1-4) were isolated as active principle. The structures of 1-4 were elucidated by the physicochemical and spectral data as rhamnetin 3-O-alpha-L-rhamnoside (1), quercetin 3-O-alpha-L-rhamnoside (2), rhamnocitrin 3-O-alpha-L-rhamnoside (3), and kaempferol 3-O-alpha-L-rhamnoside (4).

Synthesis of alkyl-alpha-L-rhamnosides by water soluble alcohols enzymatic glycosylation

The synthesis of alkyl-alpha-rhamnosides by alpha-rhamnosidase was studied using rhamnose and rhamnosides, particularly the flavonoid naringin, as glycosylation agents, and water soluble alcohols as acceptors. The reaction products were analyzed by HPLC chromatography and identified by 13C y 1H NMR. The glycosylation of alcohols by reverse hydrolysis was maximum for 40% methanol, 30% ethanol, 10% propanol and 20% isopropanol. Under optimum conditions the yield of rhamnose to alkyl-alpha-rhamnoside transformation decreased from 68% for methyl-alpha-rhamnoside to 10% for isopropyl-alpha-rhamnoside. The time course of rhamnosylations produced using naringin as the donor was comparable with that of the reverse hydrolysis obtained at the same molar concentration of the donor. The flavonoids and their derivatives remaining in the solution after the glycosylation were removed by ion exchange QEAE chromatography at pH 10. These results indicate that both, reverse hydrolysis and glycosylation by naringin are acceptable procedures for the enzymatic synthesis of short chain length alkyl-alpha-L-rhamnosides.

Two new phenylpropanoid esters of rhamnose from Lagotis yunnanensis

Two new phenylpropanoid esters of rhamnose, lagotoside B (1) and lagotoside C (2), together with three known compounds (3-5), were isolated from Lagotis yunnanensis. The structures of 1 and 2 were elucidated by spectroscopic methods. Compounds 3-5 have been obtained from this species for the first time.

Structure of the N-acetyl-l-rhamnosamine-containing O-polysaccharide of Proteus vulgaris TG 155 from a new Proteus serogroup, O55

The O-polysaccharide of the lipopolysaccharide (LPS) of Proteus vulgaris TG 155 was found to contain 2-acetamido-2,6-dideoxy-L-mannose (N-acetyl-L-rhamnosamine, L-RhaNAc), a monosaccharide that occurs rarely in Nature. The following structure of the O-polysaccharide was established by NMR spectroscopy, including 2D COSY, TOCSY, ROESY and 1H,13C HSQC experiments, along with chemical methods: [carbohydrate structure in text] Rabbit polyclonal O-antiserum against P. vulgaris TG 155 reacted with both core and O-polysaccharide moieties of the homologous LPS but showed no cross-reactivity with other LPS from the complete set of serologically different Proteus strains. Based on the unique O-polysaccharide structure and the serological data, we propose classifying P. vulgaris TG 155 into a new, separate Proteus O-serogroup, O55.

Glycosylation of N-acetylglucosamine: imidate formation and unexpected conformation

[structure: see text] Rhamnosylation in mild conditions of a disaccharide containing N-acetylglucosamine afforded the imidate 6 while at higher temperature and concentration of promoter trisaccharide 7 was isolated. The kinetic imidate 6 was independently rearranged in 50% yield to the thermodynamic trisaccharide 7. Comparative NMR studies of 7 in CDCl(3) and DMSO-d(6) suggest the formation of a nonchair conformation in CDCl(3). The structure of 7 was confirmed through the independent synthesis of the N-acetylacetamido trisaccharide 11.

Chemoenzymatic syntheses of (-)-1-deoxymannojirimycin (DMJ) and its naturally occurring 6-O-alpha-L-rhamnopyranosyl glycoside

The naturally occurring sugar mimetic alkaloids 1-deoxymannojirimycin (DMJ, 1) and 6-O-alpha-L-rhamnopyranosyl-DMJ (2) have each been prepared in a completely stereoselective manner from the cis-1,2-dihydrocatechol 3, itself obtained in enantiomerically pure form by microbial oxidation of chlorobenzene.

The 4,6-O-[alpha-(2-(2- iodophenyl)ethylthiocarbonyl)benzylidene] protecting group: stereoselective glycosylation, reductive radical fragmentation, and synthesis of beta-D-rhamnopyranosides and other deoxy sugars

[reaction: see text] In the thioglycoside/BSP/Tf(2)O glycosylation method, the 4,6-O-[alpha-(2-(2-iodophenyl)ethylthiocarbonyl)benzylidene] group enforces beta-selectivity in mannopyranosylations. Following glycosylation, treatment with Bu(3)SnH in toluene at reflux affords regioselective, reductive fragmentation to the 6-deoxy-beta-mannosides (beta-rhamnosides). Applied to glucosides, the radical fragmentation provides 6-deoxyglucosides, whereas 4-deoxygalactosides are the preferred products in the galactose series. The radical fragmentation is fully compatible with the presence of benzyl and p-methoxybenzyl ethers and with acetate esters

Direct synthesis of the beta-l-rhamnopyranosides

The direct formation of beta-l-rhamnopyranosides by means of thioglycoside donors protected with a 2-O-sulfonate ester and, ideally, a 4-O-benzoyl ester, is reported. Activation is achieved with the combination of 1-benzenesulfinyl piperidine and triflic anhydride in the presence of 2,4,6-tri-tert-butylpyrimidine. Selectivities vary from moderate to good, and the sulfonyl group is easily removed post-glycosylation with sodium amalgam in 2-propanol.

Primary cell wall composition of bryophytes and charophytes

Major differences in primary cell wall (PCW) components between non-vascular plant taxa are reported. (1) Xyloglucan: driselase digestion yielded isoprimeverose (the diagnostic repeat unit of xyloglucan) from PCW-rich material of Anthoceros (a hornwort), mosses and both leafy and thalloid liverworts, as well as numerous vascular plants, showing xyloglucan to be a PCW component in all land plants tested. In contrast, charophycean green algae (Klebsormidium flaccidium, Coleochaete scutata and Chara corallina), thought to be closely related to land plants, did not contain xyloglucan. They did not yield isoprimeverose; additionally, charophyte material was not digestible with xyloglucan-specific endoglucanase or cellulase to give xyloglucan-derived oligosaccharides. (2) Uronic acids: acid hydrolysis of PCW-rich material from the charophytes, the hornwort, thalloid and leafy liverworts and a basal moss yielded higher concentrations of glucuronic acid than that from the remaining land plants including the less basal mosses and all vascular plants tested. Polysaccharides of the hornwort Anthoceros contained an unusual repeat-unit, glucuronic acid-alpha(1-->3)-galactose, not found in appreciable amounts in any other plants tested. Galacturonic acid was consistently the most abundant PCW uronic acid, but was present in higher concentrations in acid hydrolysates of bryophytes and charophytes than in those of any of the vascular plants. Mannuronic acid was not detected in any of the species surveyed. (3) Mannose: acid hydrolysis of charophyte and bryophyte PCW-rich material also yielded appreciably higher concentrations of mannose than are found in vascular plant PCWs. (4) Mixed-linkage glucan (MLG) was absent from all algae and bryophytes tested; however, upon digestion with licheninase, PCW-rich material from the alga Ulva lactuca and the leafy liverwort Lophocolea bidentata yielded penta- to decasaccharides, indicating the presence of MLG-related polysaccharides. Our results show that major evolutionary events are often associated with changes in PCW composition. In particular, the acquisition of xyloglucan may have been a pre-adaptive advantage that allowed colonization of land.

DNA gyrase interaction with coumarin-based inhibitors: the role of the hydroxybenzoate isopentenyl moiety and the 5'-methyl group of the noviose

DNA gyrase is a major bacterial protein that is involved in replication and transcription and catalyzes the negative supercoiling of bacterial circular DNA. DNA gyrase is a known target for antibacterial agents since its blocking induces bacterial death. Quinolones, coumarins, and cyclothialidines have been designed to inhibit gyrase. Significant improvements can still be envisioned for a better coumarin-gyrase interaction. In this work, we obtained the crystal costructures of the natural coumarin clorobiocin and a synthetic analogue with the 24 kDa gyrase fragment. We used isothermal titration microcalorimetry and differential scanning calorimetry to obtain the thermodynamic parameters representative of the molecular interactions occurring during the binding process between coumarins and the 24 kDa gyrase fragment. We provide the first experimental evidence that clorobiocin binds gyrase with a stronger affinity than novobiocin. We also demonstrate the crucial role of both the hydroxybenzoate isopentenyl moiety and the 5'-alkyl group on the noviose of the coumarins in the binding affinity for gyrase.

Hepatoprotective phenylpropanoids from Scrophularia buergeriana roots against CCl(4)-induced toxicity: action mechanism and structure-activity relationship

Phenylpropanoids isolated from the roots of Scrophularia buergeriana MIQ. (Scrophulariaceae) protected primary cultures of rat hepatocytes from toxicity induced by carbon tetrachloride (CCl(4) ). In this report, we show that two of these phenylpropanoids, 4-O-E- p-methoxycinnamoyl-alpha-L-rhamnopyranoside ester ( 1) and p-methoxycinnamic acid ( 3) have significant hepatoprotective activity; another phenylpropanoid used for comparison, isoferulic acid ( 11), was equally active. To determine the mechanism(s) by which these three phenylpropanoids exerted their hepatoprotective activity, we measured activities of enzymes involved in the glutathione (GSH) redox system and assayed the level of hepatic mitochondrial GSH. The GSH levels in primary cultures of rat hepatocytes were significantly reduced with CCl(4) insult, but were significantly preserved by the treatment with these three phenylpropanoids. The activities of glutathione disulfide reductase and glutathione-S-transferase which normally decrease in CCl(4) -injured rat hepatocytes were significantly preserved by the treatment with these three phenylpropanoids. In addition, in CCl(4) -injured rat hepatocytes, the increased formation of malondialdehyde, a byproduct of lipid peroxidation, was reduced by the treatment with these phenylpropanoids. We determined the essential structural moiety within these three phenylpropanoids needed to exert hepatoprotective activity. The alpha,beta-unsaturated ester moiety seemed to be essential for exerting hepatoprotective activity.

Some amino sugars structurally related to 6-deoxymannojirimycin precursors prepared from methyl 6-deoxy-2,3-O-isopropylidene-alpha-D-lyxo-hexofuranosid-5-ulose and methyl 2,3-O-isopropylidene-alpha-D-lyxo-pentodialdo-1,4-furanoside

Methyl (5S)-5-C-amino-5-cyano-5-deoxy-2,3-O-isopropylidene-alpha-D-lyxofuranoside has been synthesised from methyl 2,3-O-isopropylidene-alpha-D-lyxo-pentodialdo-1,4-furanoside, applying the Strecker synthesis. Analogously, methyl (5S) and (5R)-5-C-amino-5-cyano-5,6-dideoxy-2,3-O-isopropylidene-alpha-D-lyxo-hexofuranosides were prepared from methyl 6-deoxy-2,3-O-isopropylidene-alpha-D-lyxo-hexofuranosid-5-ulose. The 5-S configuration was unambiguously determined by single-crystal X-ray diffraction analysis of corresponding N-acetyl derivatives. Conformations of five-membered rings are discussed. The conversion of N-acetylated amino nitriles to N-acetylamino acid ethyl ester and amide, respectively, is also described.

Genes for the biosynthesis of spinosyns: applications for yield improvement in Saccharopolyspora spinosa

Spinosyns A and D are the active ingredients in an insect control agent produced by fermentation of Saccharopolyspora spinosa. Spinosyns are macrolides with a 21-carbon, tetracyclic lactone backbone to which the deoxysugars forosamine and tri-O-methylrhamnose are attached. The spinosyn biosynthesis genes, except for the rhamnose genes, are located in a cluster that spans 74 kb of the S. spinosa genome. DNA sequence analysis, targeted gene disruptions and bioconversion studies identified five large genes encoding type I polyketide synthase subunits, and 14 genes involved in sugar biosynthesis, sugar attachment to the polyketide or cross-bridging of the polyketide. Four rhamnose biosynthetic genes, two of which are also necessary for forosamine biosynthesis, are located outside the spinosyn gene cluster. Duplication of the spinosyn genes linked to the polyketide synthase genes stimulated the final step in the biosynthesis--the conversion of the forosamine-less pseudoaglycones to endproducts. Duplication of genes involved in the early steps of deoxysugar biosynthesis increased spinosyn yield significantly.

Enantioselective synthesis of N-Cbz-protected 6-amino-6-deoxymannose, -talose, and -gulose

The enantioselective synthesis of three 6-amino-6-deoxy sugars has been achieved in six to eight steps from furfural. A sequence of diastereoselective oxidation and reduction reactions produced Cbz-protected 6-aminomannose from furfuryl alcohol 3. The incorporation of a Mitsunobu reaction into the reaction sequence allows for the selective synthesis of both N-Cbz-protected 6-aminotalose and 6-aminogulose. The overall procedure allows for the synthesis of either enantiomer of these three aminosugars. [reaction: see text]

Synthesis and structure determination of some sugar amino acids related to alanine and 6-deoxymannojirimycin

(5'R)-5'-Methyl-5'-[methyl (4S)-2,3-O-isopropylidene-beta-L-erythrofuranosid-4-C-yl]-imidazolidin-2',4'-dione was synthesised starting from methyl 6-deoxy-2,3-O-isopropylidene-alpha-D-lyxo-hexofuranosid-5-ulose applying the Bucherer-Bergs reaction. Its 5'-R configuration was confirmed by X-ray crystallography. Corresponding alpha-amino acid-methyl (5R)-5-amino-5-C-carboxy-5,6-dideoxy-alpha-D-lyxo-hexofuranoside (alternative name: 2-[methyl (4S)-2,3-O-isopropylidene-beta-L-erythrofuranosid-4-C-yl]-D-alanine) was obtained from the above hydantoin by acid hydrolysis of the isopropylidene group followed by basic hydrolysis of the hydantoin ring. Total deprotection afforded 5-C-carboxy-6-deoxymannojirimycin. Analogously, methyl (5S)-5-amino-5-C-carboxy-5,6-dideoxy-alpha-L-lyxo-hexofuranoside and 5-C-carboxy-6-deoxy-L-mannojirimycin were prepared from the corresponding (5'S)-5'-methyl-5'-[methyl (4R)-2,3-O-isopropylidene-beta-D-erythrofuranosid-4-C-yl]-imidazolidin-2',4'-dione starting from methyl 6-deoxy-2,3-O-isopropylidene-alpha-L-lyxo-hexofuranosid-5-ulose.

Beta-selective O-rhamnosylation with a rhamnosyl trichloroacetimidate that has the 4C1 conformation

A beta-selective rhamnosylation reaction was accomplished by using 2-O-benzyl-3-O-tert-butyldimethylsilyl-4-O-tertbutyldiphenylsilyl-alpha-L-rhamnopyranosyl trichloroacetimidate and a catalytic amount of 9-borabicylco[3.3.1]nonyl trifluoromethanesulfonate. The rhamnosyl donor has the 4C1 ring conformation to change the general high alpha-selectivity of the rhamnosylation reactions.

Swarming of Pseudomonas aeruginosa is dependent on cell-to-cell signaling and requires flagella and pili

We describe swarming in Pseudomonas aeruginosa as a third mode of surface translocation in addition to the previously described swimming and twitching motilities. Swarming in P. aeruginosa is induced on semisolid surfaces (0.5 to 0.7% agar) under conditions of nitrogen limitation and in response to certain amino acids. Glutamate, aspartate, histidine, or proline, when provided as the sole source of nitrogen, induced swarming, while arginine, asparagine, and glutamine, among other amino acids, did not sustain swarming. Cells from the edge of the swarm were about twice as long as cells from the swarm center. In both instances, bacteria possessing two polar flagella were observed by light and electron microscopy. While a fliC mutant of P. aeruginosa displayed slightly diminished swarming, a pilR and a pilA mutant, both deficient in type IV pili, were unable to swarm. Furthermore, cells with mutations in the las cell-to-cell signaling system showed diminished swarming behavior, while rhl mutants were completely unable to swarm. Evidence is presented for rhamnolipids being the actual surfactant involved in swarming motility, which explains the involvement of the cell-to-cell signaling circuitry of P. aeruginosa in this type of surface motility.

A rhamnolipid biosurfactant reduces cadmium toxicity during naphthalene biodegradation

A model cocontaminated system was developed to determine whether a metal-complexing biosurfactant, rhamnolipid, could reduce metal toxicity to allow enhanced organic biodegradation by a Burkholderia sp. isolated from soil. Rhamnolipid eliminated cadmium toxicity when added at a 10-fold greater concentration than cadmium (890 microM), reduced toxicity when added at an equimolar concentration (89 microM), and had no effect at a 10-fold smaller concentration (8.9 microM). The mechanism by which rhamnolipid reduces metal toxicity may involve a combination of rhamnolipid complexation of cadmium and rhamnolipid interaction with the cell surface to alter cadmium uptake.

Role of rhamnolipid biosurfactants in the uptake and mineralization of hexadecane in Pseudomonas aeruginosa

A study was undertaken to investigate the mechanisms for biosurfactant-enhanced hexadecane uptake into Pseudomonas aeruginosa. Two strains of Ps. aeruginosa were studied, one producing rhamnolipids (PG201) and the other rhamnolipid deficient (UO299). Rhamnolipids produced by PG201 acted to increase the solubility of n-hexadecane in the culture medium (from 1.84 to 22.76 microg l(-1). Rates of(l4)C-n-hexadecane uptake and mineralization were higher in PG201 than in UO299. However, the degree of difference was lower than expected. Additional studies were carried out on the cell surface properties of the two strains. During growth on n-hexadecane, the cell surface hydrophobicity of both PG201 (50.5%) and UO299 (33.7%) increased compared with that observed in water-soluble growth substrates (7-8%). Studies were also carried out to ascertain any energy requirements for the transport of n-hexadecane into Ps. aeruginosa cells. The addition of CCCP (an inhibitor of cytochrome oxidase which thereby blocks oxidative phosphorylation) at a range of concentrations caused a marked decrease in n-hexadecane uptake, indicating that n-hexadecane uptake in Ps. aeruginosa is an energy-dependent process. These studies support the hypothesis of alkane transport into microbial cells by direct contact with larger alkane droplets and by pseudosolubilization. Also, it appears that both mechanisms occur simultaneously.

Decreased virulence of a strain of Pseudomonas aeruginosa O12 overexpressing a chromosomal type 1 beta-lactamase could be due to reduced expression of cell-to-cell signaling dependent virulence factors

Pseudomonas aeruginosa produces a large variety of virulence factors and is characterized by its capacity to rapidly develop resistance when exposed to antibiotics. In order to evaluate a possible correlation between acquired resistance to antibiotics and virulence, we examined the virulence of four isogenic variants of P. aeruginosa O12 that differ in their resistance phenotypes to various beta-lactam antibiotics in a mouse model of acute pneumonia. Strains overproducing a chromosomal type 1 beta-lactamase were less virulent in both immunocompetent and immunosuppressed animals. Whereas the production of the exopolysaccharide alginate was similar between the four strains, extracellular virulence factors (elastase, rhamnolipid) that are controlled by the cell-to-cell signaling system circuit were detected in reduced amounts in the supernatant of the two isolates overproducing type 1 beta-lactamase. These results suggest that strains overexpressing the chromosomal type 1 beta-lactamase could be less virulent because of a reduction of cell-to-cell signaling dependent virulence factor production.