Structure and absolute configuration of an unsaturated anteiso fatty acid from Bacillus megaterium

Furan Fatty Acids in Some 20 Fungi Species: Unique Profiles and Quantities

Furan fatty acids (FuFAs) are a group of excellent antioxidants in food. Since data in fungi were scarce, 37 commercial or collected edible and meadow fungi were analyzed on FuFA patterns and contents. FuFA amounts in fresh fungi ranged from not detectable (n = 2) to 40 mg/100 g fungi dry weight. Fresh samples of the popular edible fungi genera Agaricus and Pleurotus showed comparable FuFA contents of 9.0-33 mg/100 g fungi dry weight. The unique FuFA profile of the fungi was dominated by 9-(3,4-dimethyl-5-pentylfuran-2-yl)-nonanoic acid (9D5). In addition, the uncommon 9-(3,4-dimethyl-5-butylfuran-2-yl)-nonanoic acid (9D4) was present in 30% of the samples with contents of up to 0.2 mg/100 g fungi dry weight. Countercurrent separation techniques were used to isolate the main FuFA 9D5, to verify the presence of 9D4, and to determine ultra-traces of 11-(3,4-dimethyl-5-pentylfuran-2-yl)-undecanoic acid (11D5), which may have been assimilated by the fungi from the substrate.

The discovery of combined toxicity effects and mechanisms of hexaconazole and arsenic to mice based on untargeted metabolomics

The high detected frequencies of hexaconazole (Hex) and arsenic (As) increased the probabilities of their co-existence in agricultural products. However, the combined toxicity effect and mechanism of action for these two pollutants were still unclear. In this study, an untargeted metabolomics method with ultra high performance liquid chromatography and tandem mass spectrometry (UPLC-MS/MS) was developed to monitor the changes of endogenous metabolites and metabolism pathways in mice liver. Our study revealed that significant differences in metabolomics profiles were observed after Hex, As, and Hex+As exposure for 90 d. Hex exposure altered 54 metabolites and 11 pathways significantly which were mainly lipid-related. For As exposure, 63 metabolites and 9 pathways were affected most of which were amino acid-related. Hex+As induced 93 metabolites changes with 34% was lipids and lipid-like molecules and 22% was organic acids and derivatives. Hex+As exposure shared the pathways that altered by Hex and As indicated that the interaction of Hex and As might be independent action. The results of this study could provide an important insight for understanding the mechanism of combined toxicity for Hex and As and be helpful for evaluating their health risk to human.

Detailed analysis of the fatty acid composition of six plant-pathogenic bacteria

Bacteria show distinct and characteristic fatty acid (FA) patterns which can be modified by environmental conditions. In this study, we cultivated six plant-pathogenic bacteria of agricultural concern and performed a detailed analysis of the fatty acid composition. The study covered four strains of the gram-negative Xanthomonas campestris pathovar (pv) campestris (Xcc), Xanthomonas perforans (Xp), Acidovorax citrulli (Ac) and Pseudomonas syringae pv. tomato (Pst), and two strains of the gram-positive Clavibacter michiganensis subsp. michiganensis (Cmm) and Streptomyces scabies (Ssc). After cultivation, freeze-dried bacteria samples were transesterified and analysed by gas chromatography with mass spectrometry in full scan and selected ion monitoring (SIM) modes. Altogether, 44 different FAs were detected in the six strains with individual contributions of 0.01-43.8% to the total FAs. The variety in the six strains ranged between 12 and 31 individual FAs. The FA composition of Xcc, Xp, Cmm and Ssc were dominated by iso- and anteiso-fatty acids (especially i15:0, a15:0, i16:0), which is typical for most bacteria. In contrast to this, Ac and Pst showed only saturated and monounsaturated FAs. Four of the six bacteria showed similar FA patterns as reported before in the literature. Differences were observed in the case of Cmm where many more FAs were detected in the present study. In addition, to the best of our knowledge, the FA pattern of Xp was presented for the first time.

Valuable furan fatty acids in soybeans and soy products

Furan fatty acids (FuFAs) are valuable minor compounds in our food with excellent antioxidant properties. Naturally occurring FuFAs are characterised by a central furan moiety with one or two methyl groups in β-/β’-position of the heterocycle (monomethyl- or M-FuFAs and dimethyl- or D-FuFAs). Comparably high concentrations of D-/M-FuFAs were reported in soybeans, but soy is often consumed as a processed product, such as full-fat soy flour and flakes, soy drink, tofu and texturised soy protein (TSP). Due to the chemical lability of D-/M-FuFAs, e.g. in the presence of light or oxygen, a degradation during the processing is possible. For this purpose, freshly harvested soybeans (n = 4) and differently processed soybean products (n = 22) were analysed on FuFAs. Three FuFAs, i.e. 11-(3,4-dimethyl-5-pentylfuran-2-yl)-undecanoic acid (11D5), 9-(3,4-dimethyl-5-pentylfuran-2-yl)-nonanoic acid (9D5), and 9-(3-methyl-5-pentylfuran-2-yl)-nonanoic acid (9M5), were identified and quantified in all fresh soybeans and most of the processed soy products (n = 20). A trend towards lower D-/M-FuFA contents in higher processed products was observable. Lower FuFA concentrations were usually accompanied with a decrease of the share of the less stable D-FuFAs (9D5, 11D5) in favour of the M-FuFA 9M5. Furthermore, one or two 3,4-nonmethylated furan fatty acids (N-FuFAs), i.e. 8-(5-hexylfuran-2-yl)-octanoic acid (8F6) and partly 7-(5-heptylfuran-2-yl)-heptanoic acid (7F7), were detected in all processed products, but not in the freshly harvested soybeans. Our results indicate that D-/M-/N-FuFAs may serve as suitable markers for both, careful manufacturing processes and adequate storage conditions of soy products.

Acyl-chain selectivity and physiological roles of Staphylococcus aureus fatty acid-binding proteins

Fatty acid (FA) kinase produces acyl-phosphate for the synthesis of membrane phospholipids in Gram-positive bacterial pathogens. FA kinase consists of a kinase protein (FakA) that phosphorylates an FA substrate bound to a second module, an FA-binding protein (FakB). Staphylococcus aureus expresses two distinct, but related, FakBs with different FA selectivities. Here, we report the structures of FakB1 bound to four saturated FAs at 1.6-1.93 Å resolution. We observed that the different FA structures are accommodated within a slightly curved hydrophobic cavity whose length is governed by the conformation of an isoleucine side chain at the end of the tunnel. The hydrophobic tunnel in FakB1 prevents the binding of cis-unsaturated FAs, which are instead accommodated by the kinked tunnel within the FakB2 protein. The differences in the FakB interiors are not propagated to the proteins' surfaces, preserving the protein-protein interactions with their three common partners, FakA, PlsX, and PlsY. Using cellular thermal shift analyses, we found that FakB1 binds FA in vivo, whereas a significant proportion of FakB2 does not. Incorporation of exogenous FA into phospholipid in ΔfakB1 and ΔfakB2 S. aureus knockout strains revealed that FakB1 does not efficiently activate unsaturated FAs. FakB2 preferred unsaturated FAs, but also allowed the incorporation of saturated FAs. These results are consistent with a model in which FakB1 primarily functions in the recycling of the saturated FAs produced by S. aureus metabolism, whereas FakB2 activates host-derived oleate, which S. aureus does not produce but is abundant at infection sites.

Peak AAA fatty acid homolog contaminants present in the dietary supplement l-Tryptophan associated with the onset of eosinophilia-myalgia syndrome

The eosinophilia-myalgia syndrome (EMS) outbreak that occurred in the USA and elsewhere in 1989 was caused by the ingestion of Showa Denko K.K. (SD) L-tryptophan (L-Trp). "Six compounds" detected in the L-Trp were reported as case-associated contaminants. Recently the final and most statistically significant contaminant, "Peak AAA" was structurally characterized. The "compound" was actually shown to be two structural isomers resulting from condensation reactions of L-Trp with fatty acids derived from the bacterial cell membrane. They were identified as the indole C-2 anteiso (AAA₁-343) and linear (AAA₂-343) aliphatic chain isomers. Based on those findings, we utilized a combination of on-line HPLC-electrospray ionization mass spectrometry (LC-MS), as well as both precursor and product ion tandem mass spectrometry (MS/MS) to facilitate identification of a homologous family of condensation products related to AAA₁-343 and AAA₂-343. We structurally characterized eight new AAA₁-XXX/AAA₂-XXX contaminants, where XXX represents the integer molecular ions of all the related homologs, differing by aliphatic chain length and isomer configuration. The contaminants were derived from the following fatty acids of the bacterial cell membrane, 5-methylheptanoic acid (anteiso-C8:0) for AAA₁-315; n-octanoic acid (n-C8:0) for AAA₂-315; 6-methyloctanoic acid (anteiso-C9:0) for AAA₁-329; n-nonanoic acid (n-C9:0) for AAA₂-329; 10-methyldodecanoic acid (anteiso-C13:0) for AAA₁-385; n-tridecanoic acid (n-C13:0) for AAA₂-385; 11-methyltridecanoic acid (anteiso-C14:0) for AAA₁-399; and n-tetradecanoic acid (n-C14:0) for AAA₂-399. The concentration levels for these contaminants were estimated to be 0.1-7.9 μg / 500 mg of an individual SD L-Trp tablet or capsule The structural similarity of these homologs to case-related contaminants of Spanish Toxic Oil Syndrome (TOS) is discussed.

Structure determination of disease associated peak AAA from l-Tryptophan implicated in the eosinophilia-myalgia syndrome

The eosinophilia-myalgia syndrome (EMS) outbreak of 1989 that occurred in the USA and elsewhere was caused by the ingestion of l-Tryptophan (L-Trp) solely manufactured by the Japanese company Showa Denko K.K. (SD). Six compounds present in the SD L-Trp were reported to be case-associated contaminants. However, "one" of these compounds, Peak AAA has remained structurally uncharacterized, despite the fact that it was described as "the only statistically significant (p=0.0014) contaminant". Here, we employ on-line microcapillary-high performance liquid chromatography-electrospray ionization mass spectrometry (LC-MS), and tandem mass spectrometry (MS/MS) to determine that Peak AAA is in fact two structurally related isomers. Peak AAA₁ and Peak AAA₂ differed in LC retention times, and were determined by accurate mass-LC-MS to both have a protonated molecular ion (MH⁺⁾ of mass 343.239Da (Da), corresponding to a molecular formula of C₂₁H₃₀N₂O_2, and possessing eight degrees of unsaturation (DoU) for the non-protonated molecule. By comparing the LC-MS and LC-MS-MS retention times and spectra with authentic synthetic standards, Peak AAA₁ was identified as the intermolecular condensation product of L-Trp with anteiso 7-methylnonanoic acid, to afford (S)-2-amino-3-(2-((S,E)-7-methylnon-1-en-1-yl)-1H-indol-3-yl)propanoic acid. Peak AAA₂ was determined to be a condensation product of L-Trp with decanoic acid, which produced (S)-2-amino-3-(2-((E)-dec-1-en-1-yl)-1H-indol-3-yl)propanoic acid.

Unexpected Formation of Low Amounts of (R)-Configurated anteiso-Fatty Acids in Rumen Fluid Experiments

Anteiso-fatty acids (aFA) with odd carbon number are a class of branched-chain fatty acids (BCFA) mainly produced by bacteria. Bacterial sources are also made responsible for their occurrence in the low percent-range in lipids of ruminants (meat and milk) and fish. aFAs are chiral molecules and typically occur predominantly in form of (S)-enantiomers, and their primary precursor has been noted to be isoleucine. Yet, low proportions of (R)-aFAs were also detected in fish and cheese samples. Here we investigated the potential formation of (R)-aFAs by means of incubation experiments with rumen fluid from fistulated cows. Supplementation of rumen fluid with both L- and DL-isoleucine, resulted in a significant (α <0.05) increase of the aFA concentrations but in both cases enantiopure (S)-aFAs were observed. By contrast, incubations without addition of any isoleucine lead to a significant (α <0.05) formation of small proportions of (R)-aFAs similarly to those previously observed in fish and cheese. These results were consistently reproduced in three different years with rumen fluid from different cows fed different diets. All findings point to the existence of a further biosynthesis pathway of aFAs with different stereospecificity than the classic one using isoleucine as primer.

Combined urea-thin layer chromatography and silver nitrate-thin layer chromatography for micro separation and determination of hard-to-detect branched chain fatty acids in natural lipids

A simple, fast and efficient procedure was developed for micro separation and enrichment of branched chain fatty acids (BCFA) from natural products using successive thin layer chromatography (TLC) technique coupling novel urea-TLC with AgNO3-TLC, which rely on the formation of urea adduction and AgNO3 bonding in methanol. These natural lipids contain a significant amount of straight chain fatty acids (FA). Fresh and fast urea-TLC and AgNO3-TLC plate making techniques were developed with more even coating and less coating material contamination before being utilized for separation. Goat milk fat was used as a model. Various experimental parameters that affect urea-TLC and AgNO3-TLC separation of BCFA were investigated and optimized, including coating of urea, concentration of original oil sample, mobile phase and sample application format. High efficiency of removal of straight chain FA was achieved with a low amount of sample in an easy and fast way. A total BCFA mix with much higher purity than previous studies was successfully achieved. The developed method has also been applied for the concentration and analysis of BCFA in cow milk fat and Anchovy oil.