Exometabolomics

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A model exometabolomic experiment set up from liquid culture, for LC-MS (A), and from agar plates, for MSI (B). Figure 1 Exometabolomics summary 121514 3.png
A model exometabolomic experiment set up from liquid culture, for LC–MS (A), and from agar plates, for MSI (B).

Exometabolomics, also known as 'metabolic footprinting', [1] [2] is the study of extracellular metabolites and is a sub-field of metabolomics. [3]

Contents

While the same analytical approaches used for profiling metabolites apply to exometabolomics, including liquid-chromatography mass spectrometry (LC-MS), nuclear magnetic resonance (NMR) and gas chromatography–mass spectrometry (GC–MS), analysis of exometabolites provides specific challenges and is most commonly focused on investigation of the transformations of exogenous metabolite pools by biological systems. [3] Typically, these experiments are performed by comparing metabolites at two or more time points, for example, spent vs. uninoculated/control culture media; this approach can differentiate different physiological states of wild-type yeast and between yeast mutants. [1] Since, in many cases, the exometabolite (extracellular) pool is less dynamic than endometabolite (intracellular) pools (which are often perturbed during sample processing) and chemically defined media can be used, it reduces some of the experimental challenges of metabolomics. [4]

Exometabolomics is also used as a complementary tool with genomic, transcriptomic [5] and proteomic data, to gain insight into the function of genes and pathways. Additionally, exometabolomics can be used to measure polar molecules being consumed or released by an organism, and to measure secondary metabolite production. [6] [7]

History

The study of extracellular metabolites has been prevalent in scientific literature. [8] [9] [10] However, global exometabolite profiling was only realized with recent advances allowing for improved chromatographic separation and detection of hundreds to thousands of compounds by the mid-2000s. [7] The first work to demonstrate the biological relevance of comparative profiling of exometabolite pools was not until 2003, when the term "metabolite footprinting" was coined by Jess Allen and coworkers. [1] [7] This work attracted a great deal of interest in the community, particularly for characterization of microbial metabolism. [2] The idea of the "exometabolome" encompassing the components of the exometabolite pool was not introduced until 2005. [11]

Recent advances in mass spectrometry imaging have allowed for spatial localization of released metabolites. [12] As the field of microbiology becomes increasingly more centered on microbial community structure, exometabolomics has provided for rapid understanding of metabolic interactions between two or more species. [13] Recently, exometabolomics has been used to design co-culture systems. [14] Because the analysis of extracellular metabolites allows for the predictions and determinations of metabolite exchange, exometabolomics analyses can be used for understanding community ecological networks. [15]

Analytical technologies

In principle, any technologies used for metabolomics can be used for exometabolomics. However, liquid chromatography–mass spectrometry (LC–MS) has been the most widely used. [3] As with typical metabolomic measurements, metabolites are identified based on accurate mass, retention time, and their MS/MS fragmentation patterns, in comparison to authentic standards. Chromatographies typically used are hydrophilic interaction liquid chromatography for the measurement of polar metabolites, [16] or reversed-phase (C18) chromatography for the measurement of non-polar compounds, lipids, and secondary metabolites. [17] Gas chromatography–mass spectrometry can also be used to measure sugars and other carbohydrates, and to obtain complete metabolic profiles. [18]

Because LC–MS does not give spatial data on metabolite localization, it can be complemented with mass spectrometry imaging (MSI). [3]

Applications

Exometabolomic techniques have been used in the following fields:

Functional genomics

Metabolite utilization to annotate function of unknown genes. [19]

Bioenergy

In lignocellulosic feedstock studies. [20]

Agriculture and food

Characterization of plant root exometabolites to determine how exometabolites affect Plant-growth promoting rhizobacteria. [21]

Metabolic footprinting of yeast strains for identification of yeast strains optimal for enhancing fermentation performance and positive attributes in wine. [22]

Health

Differentiating healthy versus cancerous bladder cells with metabolic footprinting. [23]

Footprinting, in combination with other techniques, for early recognition of outbreak and strain characterization. [24]

Studying aging with C. elegans exometabolomics. [25]

Extracellular metabolite analysis to evaluate pathogenic mechanism of intracellular protozoal parasite. [26]

Analysis of carbon cycling

Global carbon fixation, phytoplankton/dinoflaggelate interactions, and exometabolomics. [27]

Microbial communities

Interaction of E. coli exometabolites with C. elegans affects life span. [28]

Bacteria and yeast in dairy systems. [13]

Bioremediation

Metabolic niche partitioning

In 2010, exometabolomics analysis of the cyanobacterium, Synechococcus sp. PCC 7002 by Baran, et al. revealed that this photoautotroph could deplete a diverse pool of exogenous metabolites. [29] A follow-up exometabolomics study on sympatric microbial isolates from biological soil crust, which exist in communities with cyanobacteria in the desert soils of the Colorado Plateau, suggested that metabolite niche partitioning exists in these communities, where each isolate only utilizes 13-26% of metabolites from the soil [30]

Secondary metabolites

Metabolic footprinting for determination of antifungal substances' mode of action [31]

See also

Related Research Articles

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Metabolomics is the scientific study of chemical processes involving metabolites, the small molecule substrates, intermediates, and products of cell metabolism. Specifically, metabolomics is the "systematic study of the unique chemical fingerprints that specific cellular processes leave behind", the study of their small-molecule metabolite profiles. The metabolome represents the complete set of metabolites in a biological cell, tissue, organ, or organism, which are the end products of cellular processes. Messenger RNA (mRNA), gene expression data, and proteomic analyses reveal the set of gene products being produced in the cell, data that represents one aspect of cellular function. Conversely, metabolic profiling can give an instantaneous snapshot of the physiology of that cell, and thus, metabolomics provides a direct "functional readout of the physiological state" of an organism. There are indeed quantifiable correlations between the metabolome and the other cellular ensembles, which can be used to predict metabolite abundances in biological samples from, for example mRNA abundances. One of the ultimate challenges of systems biology is to integrate metabolomics with all other -omics information to provide a better understanding of cellular biology.

<span class="mw-page-title-main">Metabolome</span>

The metabolome refers to the complete set of small-molecule chemicals found within a biological sample. The biological sample can be a cell, a cellular organelle, an organ, a tissue, a tissue extract, a biofluid or an entire organism. The small molecule chemicals found in a given metabolome may include both endogenous metabolites that are naturally produced by an organism as well as exogenous chemicals that are not naturally produced by an organism.

<span class="mw-page-title-main">Liquid chromatography–mass spectrometry</span> Analytical chemistry technique

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<span class="mw-page-title-main">Metabolic flux analysis</span> Experimental fluxomics technique

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<span class="mw-page-title-main">Surface-assisted laser desorption/ionization</span>

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<span class="mw-page-title-main">Golm Metabolome Database</span>

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<span class="mw-page-title-main">Single-cell analysis</span> Testbg biochemical processes and reactions in an individual cell

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<span class="mw-page-title-main">Gary Siuzdak</span> American chemist

Gary Siuzdak is an American chemist best known for his work in the field of metabolomics, activity metabolomics, and mass spectrometry. His lab discovered indole-3-propionic acid as a gut bacteria derived metabolite in 2009. He is currently the Professor and Director of The Center for Metabolomics and Mass Spectrometry at Scripps Research in La Jolla, California. Siuzdak has also made contributions to virus analysis, viral structural dynamics, as well as developing mass spectrometry imaging technology using nanostructured surfaces. The Siuzdak lab is also responsible for creating the research tools eXtensible Computational Mass Spectrometry (XCMS), METLIN, METLIN Neutral Loss and Q-MRM. As of January 2021, the XCMS/METLIN platform has over 50,000 registered users.

<span class="mw-page-title-main">Secondary electrospray ionization</span>

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<span class="mw-page-title-main">XCMS Online</span> Bioinformatics software

XCMS Online is a cloud version of the original eXtensible Computational Mass Spectrometry (XCMS) technology, created by the Siuzdak Lab at Scripps Research. XCMS introduced the concept of nonlinear retention time alignment that allowed for the statistical assessment of the detected peaks across LCMS and GCMS datasets. XCMS Online was designed to facilitate XCMS analyses through a cloud portal and as a more straightforward way to analyze, visualize and share untargeted metabolomic data. Further to this, the combination of XCMS and METLIN allows for the identification of known molecules using METLIN's tandem mass spectrometry data, and enables the identification of unknown via similarity searching of tandem mass spectrometry data. XCMS Online has also become a systems biology tool for integrating different omic data sets. As of January 2021, the XCMSOnline /METLIN platform has over 44,000 registered users.

<span class="mw-page-title-main">Roy Goodacre</span> British Metabolomic expert and Mass Spectrometrist

Royston "Roy" Goodacre is Chair in Biological Chemistry at the University of Liverpool. With training in both Microbiology and Pyrolysis-Mass Spectrometry, Goodacre runs a multidisciplinary Metabolomics and Raman spectroscopy research group in the Institute of Systems, Molecular and Integrative Biology (ISMIB), and leads ISMIB's Centre for Metabolomics Research and the Laboratory for Bioanalytical Spectroscopy.

<span class="mw-page-title-main">Markus Ralser</span> Italian biologist

Markus Ralser is an Italian biologist. His main research interest is metabolism of microorganisms. He is also known for his work on the origin of metabolism during the origin of life, and proteomics.

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