Distinctive Compounds Research Articles

Insights into antioxidant activities and anti-skin-aging potential of callus extract from Centella asiatica (L.)

Formation of oxidative stress in dermal fibroblasts plays crucial roles in aging processes of skin. The use of phytochemicals that can promote capacity of fibroblasts to combat oxidative stress is an attractive strategy to prevent skin aging and promote skin beauty. Centella asiatica has been used to treat multitude of diseases for centuries. Previous investigations demonstrated that extracts from C. asiatica have a broad range of beneficial activities through their antioxidant activity. Hence, the extract from this medicinal plant could be a great candidate for anti-skin-aging agent. Callus culture offers a powerful platform for sustainable, rapid and large-scale production of phytochemicals to serve extensive demands of pharmaceutical and cosmeceutical industries. Here, we demonstrated the application of callus culture of Centella asiatica to produce bioactive metabolites. The 50% ethanolic extract of callus culture has distinctive features of chemical compositions and biological profiles. Information from HPTLC-DPPH and HPLC analysis suggested that the callus extract comprises distinctive antioxidant compounds, compared with those isolated from authentic plant. Moreover, results from cell culture experiment demonstrated that callus extract possesses promising antioxidant and anti-skin-aging activities. Pre-treatment with callus extract attenuated H2O2-induced-cytotoxicity on human dermal fibroblasts. The results from RT-qPCR clearly suggested that the upregulation of cellular antioxidant enzymes appeared to be major contributor for the protective effects of callus extract against oxidative stress. Moreover, supplementation with callus extract inhibited induction of matrix metalloprotease-9 following H2O2 exposure, suggesting its potential anti-skin-aging activity. Our results demonstrate the potential utility of C. asiatica callus extract as anti-skin-aging agent in cosmeceutical preparations.

Hydrogen Based Compounds as Energetic Catalysts for Liquid Rocket Engines: Implications and Applications

In the current scenario of space propulsion, liquid propellants have significantly proved useful in the upper stage rocket engines. Over the past couple decades, the world had inclined positively towards cryogenic fuel(s) viz., liquid oxygen and liquid hydrogen due to their high specific impulse. A higher specific impulse implies lower duration to achieve design cruise velocity for a given rocket initial and instantaneous mass. Liquid hydrogen and liquid oxygen as fuel and oxidizer can generate one of the highest enthalpy release in combustion, producing a specific impulse of up to 450 seconds at an effective exhaust velocity of 4.4 kilometres per second. Whereas, selected disadvantages are encountered in the form of storage and production. This indicates overdependence on cryogenic propellants and has necessitated the active research effort for better alternatives. As an interesting alternative, the combination of Dinitrogen Tetroxide (N2O4) and Monomethyl Hydrazine (MMH) have been used for many space applications owing to an extreme storage stability and hypergolic nature. Present study aims to express the effect of hydrogen-based compounds on the rocket performance. Four distinctive compounds from two groups of hydrogen-based compounds are tested with the varying oxidizer and fuel proportions to obtain a new, cost-effective and user-friendly composition that can be prepared at room temperature. The investigation attempt and explains the effect of hydrogen based energetic propellants using N2O4 and MMH as the base composition for upper stage performance. The work is motivated by the need of efficient space operations with attractive propulsive alternatives to minimize over-dependence on cryogenics, which will ultimately result in cost effectiveness. Various energetic materials were tested with the base composition by using standard NASA-CEA complex chemical equilibrium model. The performance was evaluated in terms of variation in specific impulse and characteristic velocity both of which are significant parameters. To, validate the practical utility, the role of chamber pressure, supersonic area ratio and optimal Oxidizer to fuel ratio (O/F) was determined. The work led to two interesting findings, a composition of beryllium hydride with base composition for high performance of rockets and the negative impact of hydrogen on liquid propellants.

Secondary Metabolite Differences between Naturally Grown and Conventional Coarse Green Tea

Crop culture conditions are one of the important interfaces between food, the environment, and health, and an essential research area for maintaining social-ecological integrity. In recent years, it has been reported that the difference in culture conditions between monoculture with external inputs (in cultura) and self-organized ecological niches (in natura) is significant for the resulting physiological property of plants. It has also been suggested that there exist metabolic proxies in various foods that can separate these two culture conditions, which does not depend on a single component but on the distribution of various compounds. However, little has been studied in a time series of replicated production to quantify the reproducibility of these metabolomic features associated with culture conditions. In this study, we obtained metabolome data of coarse green tea (Camellia sinensis) grown in the same region in Japan under both in cultura and in natura culture conditions over the course of six years, and constructed a list of multiple components that separated the effects of culture conditions by statistical analysis, and estimated the metabolic functions of the compounds that contributed to the separation. The results suggest that naturally grown samples are rich in allelochemicals, such as phytochemicals, alkaloids, phenylpropanoids, steroids, as well as the compounds related to microorganisms and vitamin B6 that imply the interactions with the soil microbiome. The estimated physiological functions of the distinctive compounds suggest that the in natura crop production is not only beneficial with known properties of maintaining ecosystem health such as soil functions and pathogen control, but also for the augmentation of the plant secondary metabolites that support long-term health protective effects.

Coffee (Coffea arabica L.) by-Products as a Source of Carotenoids and Phenolic Compounds—Evaluation of Varieties With Different Peel Color

Analysis of pulp and peels of Arabica coffee varieties with different external fruit color allowed the identification of 16 phenolic compounds using high-performance liquid chromatography with diode array detection and electrospray ionization multiple-stage mass spectrometry (HPLC-DAD-ESI-MSn). Nine chlorogenic acids, three flavan-3-ols, the xanthone mangiferin, the flavonol rutin and two anthocyanins were tentatively identified and quantified. 5-O-Caffeoylquinic acid together with a putative (epi)catechin hexoside were the predominant phenolics detected in the coffee varieties analyzed in this work. Whereas 3- and 4-caffeoylquinic acids, as well as 5-O-feruloylquinic acid were consistently found in higher quantities in the pulp than in the peels when individual varieties were compared, the opposite was found for the other phenolic compounds detected. Complementary, GC-MS after alkaline hydrolysis and trimethylsilylation permitted the identification of more than 30 constituents, including phenolic compounds and other benzenoids, caffeine, and diverse carboxylic acids. Detected anthocyanins were cyanidin-3-O-glucoside and cyanidin-3-O-rutinoside. Anthocyanin contents in orange-colored berries were lower than those in red fruits, while no anthocyanins were found in yellow-colored fruit. Among non-anthocyanin pigments, we found β-carotene and lutein in all varieties, along with other chloroplast-specific carotenoids in some accessions. In addition, saponification evidenced the presence of several xanthophyll esters. Both, chlorophyll a and b, were detected in the peels of all varieties, while only chlorophyll b was observed in the pulp. Thus, the color of yellow-peeled varieties is due to carotenoids, while that of orange and red-peeled varieties is due to both carotenoids as well as low and high levels of anthocyanins, respectively. Present results point out to the potential use of by-products of particular coffee varieties with differences in the external fruit color as a source of distinctive bioactive compounds, including anthocyanins and carotenoids, with health benefits.

Engineering the Unicellular Alga Phaeodactylum tricornutum for Enhancing Carotenoid Production.

Microalgae represent a promising resource for the production of beneficial natural compounds due to their richness in secondary metabolites and easy cultivation. Carotenoids feature among distinctive compounds of many microalgae, including diatoms, which owe their golden color to the xanthophyll fucoxanthin. Carotenoids have antioxidant, anti-obesity and anti-inflammatory properties, and there is a considerable market demand for these compounds. Here, with the aim to increase the carotenoid content in the model diatom Phaeodactylum tricornutum, we exploited genetic transformation to overexpress genes involved in the carotenoid biosynthetic pathway. We produced transgenic lines over-expressing simultaneously one, two or three carotenoid biosynthetic genes, and evaluated changes in pigment content with high-performance liquid chromatography. Two triple transformants over-expressing the genes Violaxanthin de-epoxidase (Vde), Vde-related (Vdr) and Zeaxanthin epoxidase 3 (Zep3) showed an accumulation of carotenoids, with an increase in the fucoxanthin content up to four fold. Vde, Vdr and Zep3 mRNA and protein levels in the triple transformants were coherently increased. The exact role of these enzymes in the diatom carotenoid biosynthetic pathway is not completely elucidated nevertheless our strategy successfully modulated the carotenoid metabolism leading to an accumulation of valuable compounds, leading the way toward improved utilization of microalgae in the field of antioxidants.

Novel analytical approach to find distinctive odor compounds from garlic cloves infested by the potato-rot nematode Ditylenchus destructor using gas chromatography–olfactometry (GC–O) with heart-cut enrichment system

The potato-rot nematode Ditylenchus destructor (Tylenchida: Anguinidae) causes severe damage to garlic production in Japan. Nematode-contaminated garlic seed cloves are often used for planting, because nematode-infested cloves are difficult to discriminate from healthy ones. To be able to find nematode-infested garlic in a nondestructive way, here this study introduced a novel analytical system of GC–O and GC–MS with heart-cut enrichment technique. The objective of this research was to find an analytical approach to identify the existence of subjectively perceptible odors which derive from the garlic infested with the nematode and to evaluate the effectiveness of those novel analytical systems. Ten odor activities associated with nematode-infested garlic were detected by the system, and “allyl methyl sulfide” and “2-methyl-1-butanol” were identified as major odor compounds (1-propanethiol was candidate). This result suggests that the novel analytical technique introduced in this study delivered sufficient data to identify the odor compounds from infested garlics. Two distinctive odor compounds might be used as indicators to detect nematode-infested garlic cloves with nondestructive way.

Lichens in Genus Parmelia: An Overview and their Application.

Parmelia that belongs to the Parmeliaceae Family is a foliose lichen combined with one or two groups of fungi in Phylum Ascomycota or Basidiomycota and algae, which might be green algae or blue-green algae (cyanobacteria). It is generally called "Stone Flower," "Charila," "Pattharphool," or "Shilaaapushpa" in India. Lichen can be generally found growing on walls, old trees and spread largely across India, especially in the mountain area. It is a source of edible organisms for people residing in some regions of Nepal and it is also cultivated in hillsides of Kashmir. It has been found that lichen contains a lot of distinctive chemical compounds such as evernic acid, lecanoric acid, lobaric acid, norstictic acid, physodic acid, and salazinic acid. Some species of this lichen are recommended traditionally for controlling diseases such as boils, bronchitis, inflammations, excessive salivation, toothache, vomiting, etc. It has also applied as an indicator for biomonitoring, astringent, carminative, demulcent, bitter, resolvent, emollient, laxative, sporofic, sedative, diuretic and considered for treating sores, bronchitis, excessive salivation, vomiting, tooth-ache, boils and inflammations. It has been utilized for preparing traditional food and acts as a bioindicator for air pollution and radiation. It shows antibacterial, antioxidant, antimycobacterial and antifungal activities, including haemolytic, anaesthetic, spasmolytic and antispasmodic and antitumour activities. It also has several unique phytoconstituents that could be in charge of different therapeutic activities, but the majority of them are still unexplored. The review mainly focuses on various facets, such as common names, synonyms, traditional uses, botanical descriptions, and pharmacological activities of seven species of Parmelia.

Functional Characterization of the Grapevine γ-Glutamyl Transferase/Transpeptidase (E.C. 2.3.2.2) Gene Family Reveals a Single Functional Gene Whose Encoded Protein Product Is Not Located in Either the Vacuole or Apoplast.

γ-glutamyl transferases/transpeptidases (E.C. 2.3.2.2, GGTs) are involved in the catabolism of many compounds that are conjugated to glutathione (GSH), which have a variety of roles. GSH can act as storage and transport vehicle for reduced sulfur; it is involved in the detoxification of xenobiotics and also acts as a redox buffer by utilizing its thiol residue to protect against reactive oxygen species, which accumulate in response to biotic and abiotic stress. Furthermore, many distinctive flavor and aroma compounds in Sauvignon blanc wines originate from odorless C5- and C6-GSH conjugates or their GGT catabolized derivatives. These precursors are then processed into their volatile forms by yeast during fermentation. In many plant species, two or more isoforms of GGTs exist that target GSH-conjugates to either the apoplast or the vacuole. A bioinformatics approach identified multiple GGT candidates in grapevine (Vitis vinifera). However, only a single candidate, VvGGT3, has all the conserved residues needed for GGT activity. This is intriguing given the variety of roles of GSH and GGTs in plant cells. Characterization of VvGGT3 from cv. Sauvignon blanc was then undertaken. The VvGGT3 transcript is present in roots, leaves, inflorescences, and tendril and at equal abundance in the skin, pulp, and seed of mature berries and shows steady accumulation over the course of whole berry development. In addition, the VvGGT3 transcript in whole berries is upregulated upon Botrytis cinerea infection as well as mechanical damage to leaf tissue. VvGGT3-GFP fusion proteins transiently over-expressed in onion cells were used to study subcellular localization. To confirm VvGGT3 activity and localization in vivo, the fluorescent γ-glutamyl-7-amido-4-methylcoumarin substrate was added to Nicotiana benthamiana leaves transiently over-expressing VvGGT3. In combination, these results suggest that the functional VvGGT3 is associated with membrane-like structures. This is not consistent with its closely related functionally characterized GGTs from Arabidopsis, radish and garlic.

Mass spectrometry-based metabolomics approach to reveal differential compounds in pufferfish soups: Flavor, nutrition, and safety

Some Eastern Asian countries deem pufferfish – especially its muscle – a culinary delight. Herein, molecular mass fingerprinting of soups prepared by Takifugu flavidus, Takifugu obscurus and Takifugu rubripes was established via matrix-assisted laser desorption/ionization – mass spectrometry (MALDI MS). Soup samples were directly analyzed by MALDI MS to collect mass spectra within 0–700 Da in a quick way, followed by principal component analysis to distinguish the different soups and to find out the distinctive compounds among the soups. High performance liquid chromatography – tandem MS (HPLC-MS/MS) was applied to identify the compounds. Nineteen compounds were identified from the HPLC-MS/MS data by using METLIN database. Through literature mining, we found that these compounds are closely related to the flavor, nutrition, and safety of pufferfish soups. This method can also be used as a facile way to distinguish between different pufferfish fillets when morphological characters have been damaged or destroyed.

Nitrogen-Centered Concave Molecules with Double Fused Pentagons.

Distinctive concave compounds bearing a nitrogen core and double fused pentagons were synthesized with a palladium-catalyzed intramolecular coupling of 1-chloro-8 H-indolo[3,2,1- de]acridine as the key step. Structural analysis confirmed the formation of bowl-shaped molecules. Experimental characterizations and theoretical calculations reveal the incorporation of nitrogen is crucial to alleviate the pentagon fusing strain, as well as in property regulation.

In Vitro Anticollagenase and Antielastase Activities of Essential Oil of Helichrysum italicum subsp. italicum (Roth) G. Don.

The chemical composition of the essential oil of flowering aerial parts of Helichrysum italicum subsp. italicum cultivated in central Italy, Marche region, was analyzed by means of gas chromatography-mass spectrometry. Seventy-eight components, accounting for 98.71% of the whole essential oil composition, were identified and quantified. Neryl acetate showed the largest relative abundance in the composition, accounting for 15.75% of the oil, followed by α-pinene (8.21%); 4,6,9-trimethyl-8-decene-3,5-dione, (Italidione I), (7.34%); ar-curcumene and β-selinene (5.37%); γ-curcumene (4.83%); nerol (4.75%); α-selinene (4.68%); limonene (4.55%); linalool (4.42%), and 2,4,6,9-tetramethyl-8-decene-3,5-dione (Italidione II), (4.26%). The oil inhibited in vitro collagenase and elastase activities, with IC50 values of 36.99 ± 1.52 and 135.43 ± 6.32 μg/mL, respectively. Neryl acetate, nerol, and linalool, distinctive compounds of the oil obtained from this plant, tested alone or in mixture, at the same percentages shown in the essential oil, exhibited no activity against the two enzymes. On the contrary, α-pinene and limonene, tested alone and in mixture, showed inhibitory activity on both collagenase and elastase.

Zerovalent Rhodium and Iridium Silatranes Featuring Two-Center, Three-Electron Polar σ Bonds.

Species with 2-center, 3-electron (2c/3e- ) σ bonds are of interest owing to their fascinating electronic structures and potential for interesting reactivity patterns. Report here is the synthesis and characterization of a pair of zerovalent (d9 ) trigonal pyramidal Rh and Ir complexes that feature 2c/3e- σ bonds to the Si atom of a tripodal tris(phosphine)silatrane ligand. X-ray diffraction, continuous wave and pulse electron paramagnetic resonance, density-functional theory calculations, and reactivity studies have been used to characterize these electronically distinctive compounds. The data available highlight a 2c/3e- bonding framework with a σ*-SOMO of metal 4- or 5dz 2 parentage that is partially stabilized by significant mixing with Si (3pz ) and metal (5- or 6pz ) orbitals. Metal-ligand covalency thus buffers the expected destabilization of transition-metal (TM)-silyl σ*-orbitals by d-p mixing, affording well-characterized examples of TM-main group, and hence polar, 2c/3e- σ "half-bonds".

Zerovalent Rhodium and Iridium Silatranes Featuring Two‐Center, Three‐Electron Polar σ Bonds

AbstractSpecies with 2‐center, 3‐electron (2c/3e−) σ bonds are of interest owing to their fascinating electronic structures and potential for interesting reactivity patterns. Report here is the synthesis and characterization of a pair of zerovalent (d9) trigonal pyramidal Rh and Ir complexes that feature 2c/3e− σ bonds to the Si atom of a tripodal tris(phosphine)silatrane ligand. X‐ray diffraction, continuous wave and pulse electron paramagnetic resonance, density‐functional theory calculations, and reactivity studies have been used to characterize these electronically distinctive compounds. The data available highlight a 2c/3e− bonding framework with a σ*‐SOMO of metal 4‐ or 5dz2 parentage that is partially stabilized by significant mixing with Si (3pz) and metal (5‐ or 6pz) orbitals. Metal‐ligand covalency thus buffers the expected destabilization of transition‐metal (TM)‐silyl σ*‐orbitals by d–p mixing, affording well‐characterized examples of TM–main group, and hence polar, 2c/3e− σ “half‐bonds”.

Electrostatic Spray Ionization-Mass Spectrometry for Direct and Fast Wine Characterization.

Due to the globally existed and economically motivated adulteration including mislabeling and/or blending, fast wine characterization is important in wine industry. Herein, we developed an electrostatic spray ionization-mass spectrometry (ESTASI-MS)-based method to distinguish wines. Wine samples were directly analyzed by ESTASI-MS without any pretreatment. Microdroplets of wine were deposited on a plastic plate for analysis. The collection of each mass spectrometric datum can be accomplished in 1–2 min without any need of pretreatment to the sample, followed by principle component analysis to discriminate wines with different labels and vintages. Long-term storage of wine was simulated and characterized by utilizing the method. High-performance liquid chromatography-MS was further applied to identify the distinctive compounds in wines to indicate their difference. We found that the method can offer a strategy for quick wine analysis, which is of practical value in wine industry for wine classification and aging control.

Distribution of Saponins in the Sea Cucumber Holothuria lessoni; the Body Wall Versus the Viscera, and Their Biological Activities.

Sea cucumbers are an important ingredient of traditional folk medicine in many Asian countries, which are well-known for their medicinal, nutraceutical, and food values due to producing an impressive range of distinctive natural bioactive compounds. Triterpene glycosides are the most abundant and prime secondary metabolites reported in this species. They possess numerous biological activities ranging from anti-tumour, wound healing, hypolipidemia, pain relieving, the improvement of nonalcoholic fatty livers, anti-hyperuricemia, the induction of bone marrow hematopoiesis, anti-hypertension, and cosmetics and anti-ageing properties. This study was designed to purify and elucidate the structure of saponin contents of the body wall of sea cucumber Holothuria lessoni and to compare the distribution of saponins of the body wall with that of the viscera. The body wall was extracted with 70% ethanol, and purified by a liquid-liquid partition chromatography, followed by isobutanol extraction. A high-performance centrifugal partition chromatography (HPCPC) was conducted on the saponin-enriched mixture to obtain saponins with a high purity. The resultant purified saponins were analyzed using MALDI-MS/MS and ESI-MS/MS. The integrated and hyphenated MS and HPCPC analyses revealed the presence of 89 saponin congeners, including 35 new and 54 known saponins, in the body wall in which the majority of glycosides are of the holostane type. As a result, and in conjunction with existing literature, the structure of four novel acetylated saponins, namely lessoniosides H, I, J, and K were characterized. The identified triterpene glycosides showed potent antifungal activities against tested fungi, but had no antibacterial effects on the bacterium Staphylococcus aureus. The presence of a wide range of saponins with potential applications is promising for cosmeceutical, medicinal, and pharmaceutical products to improve human health.

Synthesis of sulfonyloxy furoxans via hydroxyfuroxan ammonium salts

Furoxans are distinctive heteroaromatic compounds in that they are potentially capable of releasing nitric oxide under physiological conditions. In order to utilize the furoxan scaffold for the development of functional molecules, synthetically relevant functional groups are required for access to diverse furoxans. In this report, a facile route to furoxans with sulfonyloxy groups, which are halide surrogates, has been developed. The key features of this strategy include the synthesis and utilization of bench-stable hydroxyfuroxan salts, the use of sulfonyl anhydrides in the sulfonylation step instead of sulfonyl chlorides, and the photochemical isomerization of one regioisomer to another in order to gain access to both.

Translation of innovative chemistry into screening libraries: an exemplar partnership from the European Lead Factory

The identification of high-quality starting points for drug discovery is an enduring challenge in medicinal chemistry. Yet, the chemical space explored in discovery programmes tends be limited by the narrow toolkit of robust methods that are exploited in discovery workflows. The European Lead Factory (ELF) was established in 2013 to boost early-stage drug discovery within Europe. In this Feature, we describe an exemplar partnership that has led to the addition of 21119 distinctive screening compounds to the ELF Joint European Compound Library. The partnership could serve as a blueprint for the translation of innovative academic chemistry into discovery programmes.

Study of Transferability of Rubus Microsatellite Markers to Hybrid Boysenberry

Boysenberry, a Rubus hybrid between loganberry and a trailing blackberry, possesses distinctive polyphenol compounds, which have demonstrated positive biological effects on human health. Several new boysenberry genotypes have recently been developed from mutation breeding technology. In this study, a total of 103 SSR markers developed from expressed sequence tag (EST) and genomic libraries in blackberry and red raspberry were tested for cross-amplifications in 10 boysenberry genotypes. All primer pairs successfully produced amplification products, ranging from 1 to 4 loci per primer. Eleven polymorphic SSR markers (RH_MEa0007aB01, RH_MEa12cE03, RH_MEa14bF07, RH_MEa15aD04, RH_MEa13cF08, ERubLR_SQ01_N03, ERubLR_ SQ053_H01, ERubLR_SQ191_A05, RubfruitG7, Rubusr43a, and RiM019) were detected among boysenberry genotypes, while polymorphic loci were not detected in 92 markers. Polymorphism information content (PIC) and genetic diversity (GD) values ranged from 0.160 to 0.580 and from 180 to 0.640, with average values of 0.359 and 0.407, respectively, in the 11 polymorphic markers. According to a cluster analysis, all the mutant boysenberry genotypes can be classified into one category. Although the level of genetic diversity revealed by SSR markers in 10 boysenberry genotypes was low, these SSR markers will be useful for future genetic diversity, cultivar identification, QTL mapping, and gene cloning studies in boysenberry.

Making C-N and C-P bonds on the quinone derivatives through the assistance of silver-mediated C-H functionalization processes

Several multi-substituted 1,4-benzoquinone (BQ) derivatives, 4, 5, and 6, possessing C-N and C-P bonds were prepared through the assistance of silver-mediated C-H functionalization processes and characterized by spectroscopic methods. The crystal structures of some selected products were determined by X-ray diffraction methods as well. Reaction pathways are proposed to account for the formations of products from 4 to 5 then to 6. Three rather structurally distinctive compounds, 8b, 9, and 10, were obtained individually from the reactions of di-substituted compound 4aa under specified conditions. Crystal structures of these three compounds have shown that the scaffolding of each compound contains multiple fused rings. Attempts to reduce specifically the PO bond of the -P(O)Ph2 on a di-substituted 1,4-naphthoquinone N4aa to a P,N-bidentate hemilabile ligand resulted in an unexpected over-reduced compound 11. As revealed from the crystal structure of it, one of the ketone groups was completely reduced to CH2 and the other one was reduced to C-OH; yet, the targeted PO bond remains intact.

Nectar-inhabiting microorganisms influence nectar volatile composition and attractiveness to a generalist pollinator.

The plant microbiome can influence plant phenotype in diverse ways, yet microbial contribution to plant volatile phenotype remains poorly understood. We examine the presence of fungi and bacteria in the nectar of a coflowering plant community, characterize the volatiles produced by common nectar microbes and examine their influence on pollinator preference. Nectar was sampled for the presence of nectar-inhabiting microbes. We characterized the headspace of four common fungi and bacteria in a nectar analog. We examined electrophysiological and behavioral responses of honey bees to microbial volatiles. Floral headspace samples collected in the field were surveyed for the presence of microbial volatiles. Microbes commonly inhabit floral nectar and the common species differ in volatile profiles. Honey bees detected most microbial volatiles tested and distinguished among solutions based on volatiles only. Floral headspace samples contained microbial-associated volatiles, with 2-ethyl-1-hexanol and 2-nonanone - both detected by bees - more often detected when fungi were abundant. Nectar-inhabiting microorganisms produce volatile compounds, which can differentially affect honey bee preference. The yeast Metschnikowia reukaufii produced distinctive compounds and was the most attractive of all microbes compared. The variable presence of microbes may provide volatile cues that influence plant-pollinator interactions.