The Volatilome: A Vital Piece of the Complete Soil Metabolome

Soils harbor complex biological processes intertwined with metabolic inputs from microbes and plants. Measuring the soil metabolome can reveal active metabolic pathways, providing insight into the presence of specific organisms and ecological interactions. A subset of the metabolome is volatile; how...

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Bibliographic Details
Published in:	Frontiers in environmental science Vol. 9
Main Authors:	Honeker, Linnea K., Graves, Kelsey R., Tfaily, Malak M., Krechmer, Jordan E., Meredith, Laura K.
Format:	Journal Article
Language:	English
Published:	Lausanne Frontiers Research Foundation 23-04-2021 Frontiers Media S.A
Subjects:	Aerosols Analytical methods Aromatic hydrocarbons Atmospheric chemistry Bias Biodegradation Biological activity Biosynthesis Chromatography Cyclotron resonance Diterpenes Environmental degradation Environmental science Fourier transforms FT-ICR-MS Gas chromatography Gases GC-MS Mass spectrometry Mass spectroscopy Mathematical analysis Measurement methods Measurement techniques Metabolic pathways Metabolism Metabolites Metabolomics NMR Nuclear magnetic resonance Organic compounds Peatlands Resonance Scientific imaging Soil analysis soil metabolome soil microbial processes Soils VOCs Volatile organic compounds Volatility volatilome
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Summary:	Soils harbor complex biological processes intertwined with metabolic inputs from microbes and plants. Measuring the soil metabolome can reveal active metabolic pathways, providing insight into the presence of specific organisms and ecological interactions. A subset of the metabolome is volatile; however, current soil studies rarely consider volatile organic compounds (VOCs), contributing to biases in sample processing and metabolomic analytical techniques. Therefore, we hypothesize that overall, the volatility of detected compounds measured using current metabolomic analytical techniques will be lower than undetected compounds, a reflection of missed VOCs. To illustrate this, we examined a peatland metabolomic dataset collected using three common metabolomic analytical techniques: nuclear magnetic resonance (NMR), gas chromatography-mass spectroscopy (GC-MS), and fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). We mapped the compounds to three metabolic pathways (monoterpenoid biosynthesis, diterpenoid biosynthesis, and polycyclic aromatic hydrocarbon degradation), chosen for their activity in peatland ecosystems and involvement of VOCs. We estimated the volatility of the compounds by calculating relative volatility indices (RVIs), and as hypothesized, the average RVI of undetected compounds within each of our focal pathways was higher than detected compounds ( p < 0.001). Moreover, higher RVI compounds were absent even in sub-pathways where lower RVI compounds were observed. Our findings suggest that typical soil metabolomic analytical techniques may overlook VOCs and leave missing links in metabolic pathways. To more completely represent the volatile fraction of the soil metabolome, we suggest that environmental scientists take into consideration these biases when designing and interpreting their data and/or add direct online measurement methods that capture the integral role of VOCs in soil systems.
ISSN:	2296-665X 2296-665X
DOI:	10.3389/fenvs.2021.649905