Identification of odor blend used by Caenorhabditis elegans for pathogen recognition.

Identification of odor blend used by Caenorhabditis elegans for pathogen recognition.

Chem Senses. 2018 Jan 24;:

Authors: Worthy S, Rojas G, Taylor C, Glater EE

Abstract
Animals have evolved specialized pathways to detect appropriate food sources and avoid harmful ones. Caenorhabditis elegans can distinguish among the odors of various species of bacteria, its major food source, but little is known about what specific chemical cue or combination of chemical cues C. elegans uses to detect and recognize different microbes. Here, we examine the strong innate attraction of C. elegans for the odor of the pathogenic bacterium, Serratia marcescens. This initial attraction likely facilitates ingestion and infection of the C. elegans host. Using solid-phase microextraction and gas chromatography coupled with mass spectrometry, we identify five volatile odors released by S. marcescens and identify those that are attractive to C. elegans. We use genetic methods to show that the amphid chemosensory neuron, AWCON, senses both S. marcescens-released 2-butanone and acetone and drives attraction to S. marcescens. In C. elegans, pairing a single odor with food deprivation results in a reduced attractive response for that specific odor. We find that pairing the natural odor of S. marcescens with food deprivation results in a reduced attraction for the natural odor of S. marcescens and a similar reduced attraction for the synthetic blend of acetone and 2-butanone. This result indicates that only two odorants represent the more complex odor bouquet of S. marcescens. Although bacterial-released volatiles have long been known to be attractive to C. elegans, this study defines for the first time specific volatile cues that represent a particular bacterium to C. elegans.

PMID: 29373666 [PubMed - as supplied by publisher]

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Wiring taste receptor cells to the central gustatory system.

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Wiring taste receptor cells to the central gustatory system.

Oral Dis. 2018 Jan 24;:

Authors: Spielman AI, Brand JG

Abstract
Taste receptor cells in the tongue are epithelial in nature and turnover frequently. Taste receptor cell-associated neurons carrying bitter, sweet or sour signals never turnover and are hardwired to specific gustatory centers in the brain. How can ever-changing bitter or sweet receptors find never-changing neurons that must match the specificity of the signal? This article reviews a recent paper published in Nature (Lee et al., 2017, 548:330-333) that identified two molecules belonging to the semaphorin axon guidance family of molecules (SEMA3A and SEMA7A) that help maintain the "labelled line principle" between peripheral bitter or sweet receptors and their respective central projection area in the gustatory center. This article is protected by copyright. All rights reserved.

PMID: 29363231 [PubMed - as supplied by publisher]

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Neurobiology of TRP Channels

Neurobiology of TRP Channels

Book. 2017

Authors: Emir TLR

Abstract
The transient receptor potential (TRP) channels were first described in Drosophila, in which photoreceptors carrying trp gene mutations exhibited a transient voltage response to continuous light stimulation (Minke, 1977; Montell et al., 1985). Mammalian TRP channels have six subfamilies including TRPC, TRPV, TRPM, TRPA, TRPML, and TRPP (Clapham, 2003), with about 28 mammalian subfamily members, most of which have splicing variants. All TRP channels have six transmembrane domains with the N- and C-terminal regions located inside the cell and are assembled as tetramers to form nonselective cation-permeable pores (Liao et al., 2014). TRP channels are expressed in a wide variety of tissues, and they are commonly embedded either in the membrane surface or cytosolic organelles, such as endosomes and lysosomes. Activation of TRP channels generally promotes excitability of excitable cells and Ca2+ influx in many forms of cellular processes in both excitable and nonexcitable cells. The skin is divided into three layers: (1) The epidermis, the outermost layer of skin, provides a waterproof barrier and creates the skin tone. Although the most abundant cells of the epidermis are keratinocytes, there are also nonepithelial immune cells present in the epidermis, such as Langerhans cells and dendritic epidermal T cells (DETCs). (2) The dermis, directly under the epidermis, contains tough connective tissue, hair follicles (HFs), and sweat glands. The dermis also hosts different subtypes of T cells that recirculate through skin-draining lymph nodes and are involved in normal immunity as well as inflammatory skin diseases such as psoriasis (Bos et al., 1987; Streilein, 1983). In addition to T cells, the dermis is enriched with tissue macrophages and dendritic cells that originate from the yolk sac and self-renew within the skin under inflammatory conditions (Jenkins, 2011). Together with cutaneous innate immune cells, the circulating monocytes traffic through the skin to survey the environment and transport antigens to the draining lymph nodes (Jakubzick et al., 2013). (3) The deeper subcutaneous tissue (hypodermis) is made of fat and connective tissue. In the skin, TRP channels are not only expressed in sensory nerve endings but also in many nonneuronal cell populations including keratinocytes and skin-resident immune cells (Figure 6.1). Various TRP channels participate in the formation and maintenance of skin barrier, HF growth, and cutaneous immunological and inflammatory processes, thereby maintaining skin homeostasis as well as contributing to many types of skin disorders (Figure 6.2). More importantly, several skin-expressing TRP channels act as the first-order sensors of temperature, mechanical, and chemical stimuli and mediate our senses of temperature, touch, itch, and pain under both physiological and pathological conditions.

PMID: 29356485

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Phylogenetic patterns of trait and trait plasticity evolution: Insights from amphibian embryos.

Phylogenetic patterns of trait and trait plasticity evolution: Insights from amphibian embryos.

Evolution. 2018 Jan 18;:

Authors: Relyea RA, Stephens PR, Barrow LN, Blaustein AR, Bradley PW, Buck JC, Chang A, Collins JP, Crother B, Earl J, Gervasi SS, Hoverman JT, Hyman O, Lemmon EM, Luhring TM, Michelson M, Murray C, Price S, Semlitsch RD, Sih A, Stoler AB, VandenBroek N, Warwick A, Wengert G, Hammond JI

Abstract
Environmental variation favors the evolution of phenotypic plasticity. For many species, we understand the costs and benefits of different phenotypes, but we lack a broad understanding of how plastic traits evolve across large clades. Using identical experiments conducted across North America, we examined prey responses to predator cues. We quantified five life history traits and the magnitude of their plasticity for 23 amphibian species/populations (spanning three families and five genera) when exposed to no cues, crushed-egg cues, and predatory crayfish cues. Embryonic responses varied considerably among species and phylogenetic signal was common among the traits whereas phylogenetic signal was rare for trait plasticities. Among trait-evolution models, the Ornstein Uhlenbeck (OU) model provided the best fit or was essentially tied with Brownian motion. Using the best fitting model, evolutionary rates for plasticities were higher than traits for three life history traits and lower for two. These data suggest that the evolution of life history traits in amphibian embryos is more constrained by a species' position in the phylogeny than by life history plasticity. The fact that an OU model of trait evolution was often a good fit to patterns of trait variation may indicate adaptive optima for traits and their plasticities. This article is protected by copyright. All rights reserved.

PMID: 29345312 [PubMed - as supplied by publisher]

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Structure-function relationships of olfactory and taste receptors.

Structure-function relationships of olfactory and taste receptors.

Chem Senses. 2018 Jan 12;:

Authors: Behrens M, Briand L, de March CA, Matsunami H, Yamashita A, Meyerhof W, Weyand S

Abstract
The field of chemical senses has made major progress in understanding the cellular mechanisms of olfaction and taste in the past two decades. However, the molecular understanding of odour and taste recognition is still lagging far behind and will require solving multiple structures of the relevant full-length receptors in complex with native ligands to achieve this goal. However, the development of multiple complimentary strategies for the structure determination of G protein-coupled receptors (GPCRs) makes this goal realistic. The common conundrum of how multi-specific receptors that recognize a large number of different ligands results in a sensory perception in the brain will only be fully understood by a combination of high-resolution receptor structures and functional studies. This review discusses the first steps on this pathway, including biochemical and physiological assays, forward genetics approaches, molecular modelling and the first steps towards the structural biology of olfactory and taste receptors.

PMID: 29342245 [PubMed - as supplied by publisher]

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Effects of task demands on olfactory, auditory and visual event-related potentials suggest similar top-down modulation across senses.

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Effects of task demands on olfactory, auditory and visual event-related potentials suggest similar top-down modulation across senses.

Chem Senses. 2018 Jan 08;:

Authors: Andersson L, Sandberg P, Olofsson J, Nordin S

Abstract
A widely held view is that top-down modulation of sensory information relies on an amodal control network that acts through the thalamus to regulate incoming signals. Olfaction lacks a direct thalamic projection, which suggests that it may differ from other modalities in this regard. We investigated the late positive complex (LPC) amplitudes of event-related potentials (ERP) from 28 participants, elicited by intensity-matched olfactory, auditory and visual stimuli, during a condition of focused attention, a neutral condition, and a condition in which stimuli were to be actively ignored. Amplitudes were largest during the attend condition, lowest during the ignore condition, with the neutral condition in between. A Bayesian analysis resulted in strong evidence for similar effects of task across sensory modalities. We conclude that olfaction, despite its unique neural projections, does not differ from audition and vision in terms of task-dependent neural modulation of the LPC.

PMID: 29325013 [PubMed - as supplied by publisher]

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Activation of nuclear receptor PXR impairs glucose tolerance and dysregulates GLUT2 expression and subcellular localization in liver.

Activation of nuclear receptor PXR impairs glucose tolerance and dysregulates GLUT2 expression and subcellular localization in liver.

Biochem Pharmacol. 2018 Jan 05;:

Authors: Hassani-Nezhad-Gashti F, Rysä J, Kummu O, Näpänkangas J, Buler M, Karpale M, Hukkanen J, Hakkola J

Abstract
Pregnane X receptor (PXR) is a nuclear receptor that senses chemical environment and is activated by numerous clinically used drugs and environmental contaminants. Previous studies have indicated that several drugs known to activate PXR appear to induce glucose intolerance. We now aimed to reveal the role of PXR in drug-induced glucose intolerance and characterize the mechanisms involved. We used PXR knockout mice model to investigate the significance of this nuclear receptor in the regulation of glucose tolerance. PXR ligand pregnenolone-16ɑ-carbonitrile (PCN) impaired glucose tolerance in the wildtype mice but not in the PXR knockout mice. Furthermore, DNA microarray and bioinformatics analysis of differentially expressed genes and glucose metabolism relevant pathways in PCN treated primary hepatocytes indicated that PXR regulates genes involved in glucose uptake. PCN decreased the expression of glucose transporter 2 (GLUT2) in mouse liver and in the wildtype mouse hepatocytes but not in the PXR knockout cells. Data mining of published chromatin immunoprecipitation-sequencing results indicate that Glut2 gene is a direct PXR target. Furthermore, PCN induced internalization of GLUT2 protein from the plasma membrane to the cytosol in the liver in vivo and repressed glucose uptake in the primary hepatocytes. Our results indicate that the activation of PXR impairs glucose tolerance and thus PXR represents a novel diabetogenic pathway. PXR activation dysregulates GLUT2 function by two different mechanisms. These findings may partly explain the diabetogenic effects of medications and environmental contaminants.

PMID: 29309761 [PubMed - as supplied by publisher]

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Odorant Receptor Desensitization in Insects.

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Odorant Receptor Desensitization in Insects.

J Exp Neurosci. 2017;11:1179069517748600

Authors: Guo H, Smith DP

Abstract
Insects and other arthropods transmit devastating human diseases, and these vectors use chemical senses to target humans. Understanding how these animals detect, respond, and adapt to volatile odorants may lead to novel ways to disrupt host localization or mate recognition in these pests. The past decade has led to remarkable progress in understanding odorant detection in arthropods. Insects use odorant-gated ion channels, first discovered in Drosophila melanogaster, to detect volatile chemicals. In flies, 60 "tuning" receptor subunits combine with a common subunit, Orco (odorant receptor coreceptor) to form ligand-gated ion channels. The mechanisms underlying odorant receptor desensitization in insects are largely unknown. Recent work reveals that dephosphorylation of serine 289 on the shared Orco subunit is responsible for slow, odor-induced receptor desensitization. Dephosphorylation has no effect on the localization of the receptor protein, and activation of the olfactory neurons in the absence of odor is sufficient to induce dephosphorylation and desensitization. These findings reveal a major component of receptor modulation in this important group of disease vectors, and implicate a second messenger feedback mechanism in this process.

PMID: 29308015 [PubMed]

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Decreased electrogustometric taste sensitivity in patients with acquired olfactory dysfunction.

Decreased electrogustometric taste sensitivity in patients with acquired olfactory dysfunction.

Rhinology. 2018 Jan 07;:

Authors: Han P, Georgi M, Cuevas M, Haehner A, Gudziol V, Hummel T

Abstract
BACKGROUND: Cross-modal chemosensory dysfunction between olfaction and gustation is not well known.
METHODOLOGY: 180 participants were classified into three groups (60 with olfactory dysfunction, 60 with gustatory dysfunction and 60 healthy controls without chemosensory dysfunction). Olfactory functions were obtained with Sniffin Sticks; gustatory function was measured by suprathreshold gustatory stimuli (taste sprays) and a quasi-threshold measure of taste function (taste strips) for five taste qualities (sweet, salty, sour, bitter and umami). Electric taste threshold was measured using electrogustometry (EGM). In addition, group differences in dietary behaviors were investigated with a specifically designed questionnaire.
RESULTS: Patients with olfactory dysfunction had increased electric taste thresholds and decreased scores for the umami taste strip test as compared to healthy controls. Overall there was no major difference between patients with chemosensory dysfunction and healthy controls regarding dietary behaviors, although some patients certainly exhibited dietary problems. Importantly, patients with taste loss, but not patients with smell loss, exhibited a higher degree of depression than controls.
CONCLUSION: Patients with olfactory dysfunction showed decreased taste sensitivity which suggested an interaction between the chemical senses taste, trigeminal function, and olfaction. This provides the basis for including both smell and taste psychophysical assessment in clinical practices. In addition, patients with taste loss appeared to suffer most from chemosensory dysfunction.

PMID: 29306960 [PubMed - as supplied by publisher]

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Enhancement of saltiness perception by monosodium glutamate taste and soy sauce odor: a near-infrared spectroscopy study.

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Enhancement of saltiness perception by monosodium glutamate taste and soy sauce odor: a near-infrared spectroscopy study.

Chem Senses. 2018 Jan 03;:

Authors: Onuma T, Maruyama H, Sakai N

Abstract
Previous studies have reported that the umami taste of monosodium L-glutamate (MSG) and salty-smelling odors (e.g., soy sauce, bacon, sardines) enhance the perception of saltiness. This study aimed to investigate the neural basis of the enhancement of saltiness in human participants using functional near-infrared spectroscopy (fNIRS). University students who had passed a taste panel test participated in this study. Sodium chloride solutions were presented with or without either 0.10% MSG or the odor of soy sauce. The participants were asked to drink a cup of the stimulus and to evaluate only saltiness intensity in Experiment 1, as well as other sensory qualities in Experiment 2, and temporal brain activity was measured using fNIRS. In Experiment 3, the participants were asked to evaluate saltiness intensity using the time-intensity (TI) method, and the response of the parotid salivary glands was measured using fNIRS. The fNIRS data showed that the added MSG and soy sauce enhanced the hemodynamic response in temporal brain regions, including the frontal operculum, but no effect on the hemodynamic salivary responses was detected. These results indicate that the perceived enhancement of saltiness occurs in the brain region that is involved in central gustatory processing. Furthermore, the results of the sensory evaluations suggest that enhancement of saltiness by the addition of MSG is mainly based on fusion of the salty-like property of MSG and saltiness of NaCl, whereas enhancement by the addition of soy sauce odor is mainly based on modulation of the temporal dynamics of saltiness perception.

PMID: 29304190 [PubMed - as supplied by publisher]

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Testing olfactory function and mapping the structural olfactory networks in the brain.

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Testing olfactory function and mapping the structural olfactory networks in the brain.

Dan Med J. 2018 Jan;65(1):

Authors: Fjældstad A

Abstract
We perceive the world through our senses. The dependence on these sensory stimuli becomes obvious when we see a visually impaired individual with a guide dog or an individual using sign language. However, individuals with olfactory deficits suffer from a more concealed impairment without any opportunity for diagnostics or treatment in the Danish healthcare system. Around a fifth of the population experience olfactory deficits, of which 1-2% are functionally anosmic. The personal consequences for anosmics can be extensive, lacking not only in hedonic yield related to eating and drinking, but also the socialization during dinners can become niggling. Similarly, social attraction and repulsion can be affected, however, effects linger beyond social consequences and quality of life. An olfactory deficit is a common early symptom in several neurologic, neurodegenerative, and psychiatric diseases. These associations may be due to the central location of the primary olfactory cortex, tugged in and between hedonic hotspots of the brain, and its hard-wired structural connections to key hubs of consciousness and memory in the brain. 
A better knowledge of olfactory receptors and odour perception has emerged during the past few decades. This has given rise to a deeper understanding of the etiologies behind olfactory deficits, to the anticipation of utilising the diagnostic potential of olfaction as a prodromal marker of disease, and ultimately to the prospect of improving treatment options for these patients. Much has been accomplished within the field, but much is still beyond our grasp. 
In Denmark, the focus on olfaction and olfactory testing has been scarce, at best. The first step of my PhD was therefore a review in Danish, published in the most widely distributed and read Danish journal, "Ugeskrift for Læger", in order to raise awareness on olfactory testing and on a clinical olfactory focus in Central Denmark Region. Secondly, we validated a tool for assessing olfactory function in Danish. The Danish 12-odourant "Sniffin' Sticks" identification test (SIT-12) was modified, validated and published, which allowed us to focus on other aspects of olfactory perception and olfactory testing.
 One focus has been to investigate the possible role of overlapping volatile chemical molecules in differentiating closely related descriptors. This study was conducted in order to emphasize the need for a meticulous approach when conducting validation stud-ies of olfactory tests, especially the need for revalidation after a modification process.
 Another focus has been on investigating the differences between olfactory identification abilities in adolescents relative to adults. Previous international studies have shown that the identification skills of adolescents are significantly different from their adult compatriots. Earlier validation studies on adolescents have used the adult version of odorant descriptors as the starting point. In our study we examine the role of odour familiarity in the difference between adult and adolescent identification abilities.
 The main focus of this PhD has been to develop a method for evaluating central olfactory patency and processing, where indi-vidual preferences and sensitivity to specific odours could be removed from the equation, as these parameters has proven trou-blesome in functional neuroimaging of the olfactory system. We identified that a reference area for investigating primary olfactory processing in neuroimaging included several non-primary struc-tures and lacked the structural neural connections to key secondary olfactory areas. Consequently, we redefined the template for olfac-tory processing by combining findings from anatomical and func-tional neuroimaging studies. This has led to the creation of a struc-tural olfactory fingerprint, which is already integrated in six on-going studies as a tool to investigate pathologic and benign chang-es in structural olfactory pathways.
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PMID: 29301613 [PubMed - in process]

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Olfaction, Philosophy and the Missing Object.

Olfaction, Philosophy and the Missing Object.

Chem Senses. 2017 Dec 30;:

Authors: Lindemann B

PMID: 29300892 [PubMed - as supplied by publisher]

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Role of Endocannabinoids on Sweet Taste Perception, Food Preference, and Obesity-related Disorders.

Role of Endocannabinoids on Sweet Taste Perception, Food Preference, and Obesity-related Disorders.

Chem Senses. 2017 Dec 25;43(1):3-16

Authors: Tarragon E, Moreno JJ

Abstract
The prevalence of obesity and obesity-related disorders such as type 2 diabetes (T2D) and metabolic syndrome has increased significantly in the past decades, reaching epidemic levels and therefore becoming a major health issue worldwide. Chronic overeating of highly palatable foods is one of the main responsible aspects behind overweight. Food choice is driven by food preference, which is influenced by environmental and internal factors, from availability to rewarding properties of food. Consequently, the acquisition of a dietary habit that may lead to metabolic alterations is the result of a learning process in which many variables take place. From genetics to socioeconomic status, the response to food and how this food affects energy metabolism is heavily influenced, even before birth. In this work, we review how food preference is acquired and established, particularly as regards sweet taste; towards which flavors and tastes we are positively predisposed by our genetic background, our early experience, further lifestyle, and our surroundings; and, especially, the role that the endocannabinoid system (ECS) plays in all of this. Ultimately, we try to summarize why this system is relevant for health purposes and how this is linked to important aspects of eating behavior, as its function as a modulator of energy homeostasis affects, and is affected by, physiological responses directly associated with obesity.

PMID: 29293950 [PubMed - in process]

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Interactions of Lemon, Sucrose and Citric Acid in Enhancing Citrus, Sweet and Sour Flavors.

Interactions of Lemon, Sucrose and Citric Acid in Enhancing Citrus, Sweet and Sour Flavors.

Chem Senses. 2017 Dec 25;43(1):17-26

Authors: Veldhuizen MG, Siddique A, Rosenthal S, Marks LE

Abstract
Flavorants such as lemon extract that activate olfactory receptors may also evoke or enhance flavor qualities such as sour and sweet that are typically considered gustatory. Similarly, flavorants such as sucrose and citric acid that activate gustatory receptors may enhance flavors such as citrus that are typically considered olfactory. Here, we ask how lemon extract, sucrose, and citric acid, presented separately and together, affect sweet, sour, and citrus flavors. We accomplished this by testing, in the same 12 subjects, lemon extract and sucrose (Experiment 1), lemon extract and citric acid (Experiment 2), and lemon extract, sucrose, and citric acid (Experiment 3). Results showed that both lemon extract and citric acid increased the ratings of citrus and sour intensity. Lemon extract did not affect sweet, but citric acid did, mainly in Experiment 3. Sucrose systematically increased only sweet intensity and modulated the effect of lemon extract on sour. The most robust multiquality effect was the enhancement of sour by lemon extract. These outcomes suggest, first, a role played by experience with the statistical associations of gustatory and olfactory flavorants and, second, that lemon flavor is complex, having citrus and sour qualities that may not be fully separable in perception.

PMID: 29293949 [PubMed - in process]

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Sweet Emotion: The Role of Odor-induced Context in the Search Advantage for Happy Facial Expressions.

Sweet Emotion: The Role of Odor-induced Context in the Search Advantage for Happy Facial Expressions.

Chem Senses. 2017 Dec 23;:

Authors: Damjanovic L, Wilkinson H, Lloyd J

Abstract
The current study investigated the extent to which the concurrent presentation of pleasant and unpleasant odors could modulate the perceptual saliency of happy facial expressions in an emotional visual search task. Whilst a search advantage for happy faces was found in the no odor and unpleasant odor conditions, it was abolished under the pleasant odor condition. Furthermore, phasic properties of visual search performance revealed the malleable nature of this happiness advantage. Specifically, attention towards happy faces was optimized at the start of the visual search task for participants presented with pleasant odors, but diminished towards the end. This pattern was reversed for participants in the unpleasant odor condition. These patterns occur through the emotion-inducing capacities of odors and highlight the circumstances in which top-down factors can override perceptually salient facial features in emotional visual search.

PMID: 29293901 [PubMed - as supplied by publisher]

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Macroalgal-bacterial interactions: Role of dimethylsulfoniopropionate in microbial gardening by Ulva (Chlorophyta).

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Macroalgal-bacterial interactions: Role of dimethylsulfoniopropionate in microbial gardening by Ulva (Chlorophyta).

Mol Ecol. 2017 Dec 31;:

Authors: Kessler RW, Weiss A, Kuegler S, Hermes C, Wichard T

Abstract
The marine macroalga Ulva mutabilis (Chlorophyta) develops into callus-like colonies consisting of undifferentiated cells and abnormal cell walls under axenic conditions. U. mutabilis is routinely cultured with two bacteria, the Roseovarius sp. MS2 strain and the Maribacter sp. MS6 strain, which release morphogenetic compounds and ensure proper algal morphogenesis. Using this tripartite community as an emerging model system, we tested the hypothesis that the bacterial-algal interactions evolved as a result of mutually taking advantage of signals in the environment. Our study aimed to determine whether cross-kingdom cross-talk is mediated by the attraction of bacteria through algal chemotactic signals. Roseovarius sp. MS2 senses the known osmolyte dimethylsulfoniopropionate (DMSP) released by Ulva into the growth medium. Roseovarius sp. is attracted by DMSP and takes it up rapidly such that DMSP can only be determined in axenic growth media. As DMSP did not promote bacterial growth under the tested conditions, Roseovarius benefited solely from glycerol as the carbon source provided by Ulva. Roseovarius quickly catabolized DMSP into methanethiol (MeSH) and dimethylsulfide (DMS). We conclude that many bacteria can use DMSP as a reliable signal indicating a food source and promote the subsequent development and morphogenesis in Ulva. This article is protected by copyright. All rights reserved.

PMID: 29290092 [PubMed - as supplied by publisher]

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