Distinguishing pollutant-induced stresses from spatial and temporal environmental heterogeneity - a metabolomic approach to stress ecology

Lead Research Organisation: Imperial College London
Department Name: Dept of Surgery and Cancer


If proteins form the machinery of a cell, then small molecule metabolites are the cell's currency, forming the flows of information (signalling), energy and nutrients that regulate many of the most important biological functions. The accounting of these metabolites - by listing in an unbiased fashion all the metabolites present in a biological sample - is called metabolomics. Because of the central nature of metabolism in the control of physiology, the metabolites that are present in cells and organisms are very sensitive to environmental variation (e.g. differences in soil chemistry, climate, etc.). In recent years, the development of analytical methods to identify a large sub-set of the metabolites present in cells has held promise that such analyses could be used to establish which environmental influences were affecting an organism's health. This is important because human activity now means that in much of the developed, and increasingly the developing, world, the condition of the environment has been changed meaning that species are living within ecosystems that are no longer 'pristine'. One example of the effects of man on the environment is the presence in much of the developed and, increasingly, developing world, of a 'grey veil' of contamination resulting from domestic and industrial pollution. To date the metabolomics approach has been used mostly in laboratory-based studies to identify the responses of a range of species to environmental stresses. These stresses include pollution, as well as 'natural' factors like temperature extremes and disease. While these results have been extremely promising, a potential criticism is that it may not be as successful in the real world as it is in the lab. This is primarily because in the natural environment there are large variations in environmental factors (e.g. climate, soil/ water chemistry, interactions with other organisms), which will all also affect metabolite levels. This may make it difficult, if not impossible, to separate the effects of the factor being studied (e.g. environmental pollution) from the 'metabolic noise' created by the effects of all the other varying environmental factors. In this project we are aiming to specifically to test how reliable metabolomics can be to study the effects of soil pollution on natural populations. We will study a common British earthworm species: earthworms are good 'sentinel' species for soil contamination, as they .are both sensitive to pollution, and play an important ecological role in most soils. Initially, we will sample worms at several different times throughout the year from a wide range of clean sites across the country. This will tell us about the variety of metabolic responses that can be found in worms living under comparatively unpolluted conditions. Next we will conduct a series of laboratory experiments to understand the effects of a range of environmental factors (e.g. different soil acidity, moisture levels, soil type, temperature) on worm metabolic physiology. This will help us interpret the variations we see in our field-collected individuals: what kind of natural stresses were they under? Finally we will measure metabolites in worms collected from a set of known polluted sites (contaminated with toxic heavy metals and/or organic chemicals) at different times through the year. This will allow us to answer the fundamental question, can we reliably distinguish worms from clean and polluted sites, even though the sites themselves and the climatic condition at the time of collections are highly varied? On completion, our study will provide an extensive and high-quality dataset that could be used as a baseline for future research. Further, the results we will obtain will be of considerable academic interest to both physiologist and environmental scientists. Finally our results may, in the long run, lead to the development of methods to monitor and assess the changing state of our environment.


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Description Some data remain to be processed and papers to be published, so I expect this list to be updated in the future.

However, some key findings we have already established include:

1. a validated and reliable method for measuring metabolites from earthworms to use as environmental biomarkers.

2. identification of a suite of positively-charged metabolites in earthworms (betaines) that generally play a role in protecting against osmotic stress, and are not usually found in soil animals.

3. Characterisation of a set of compounds (which we have named 'drilodefensins') that allow earthworms to digest polyphenol-rich plant material. This has major implications for the role of earthworms in contributing to the turnover of terrestrial carbon.

4. Insight into the association of metabolome profiles with genotypes in wild earthworm populations, with implications for understanding cryptic speciation. We have also identified species-discriminatory metabolites from earthworm coelomic fluid, which include unusual metabolites (some unique - and potentially pharmacologically active).

5. The overall driver of metabolomic phenotype in earthworms is the site from which they are derived. The reasons are not fully clear but I expect it to be down to a large extent to a combination of plasticity and microevolution. One important consequence is that we now understand much better how to apply metabolomics in an environmental monitoring type context: it is misleading to analyse animals taken from a single site - or a transect across a single site - and make general conclusions about metabolic relations to toxicity. This implies that a majority of previous studies in the field are not valid, and should change the way that scientists interested in ecotoxicometabolomics set up studies in the future.
Exploitation Route The earthworm drilodefensins are potent surfactants that are chemically more like synthetic surfactants than 'normal' biosurfactants, yet they can be degraded rapidly by earthworm enzymes. This could have future biotech implications.
Sectors Agriculture, Food and Drink,Chemicals,Environment

Description Our published paper on earthworm digestion of polyphenol-rich plant material raised a lot of public interest - the article has an altmetrics score of 278. This included popularisation through a television news item, as well as interviews for both local and national radio programmes.
First Year Of Impact 2015
Sector Environment
Impact Types Societal

Title Metabolite extraction from earthworm model organism 
Description In depth optimization of techniques for sampling metabolites from Lumbricus rubellus for metabolomic analysis 
Type Of Material Biological samples 
Year Produced 2012 
Provided To Others? Yes  
Impact Publication on this technique in journal Metabolomics. 
Description Bruker Daltonics 
Organisation Bruker Corporation
Country United States 
Sector Private 
PI Contribution Providing samples and intellectual input for imaging analysis
Collaborator Contribution Providing methods and instrument access for MALDI-FT-ICR-MS imaging
Impact Paper submitted but still under review
Start Year 2013
Description Interviews and presentations for drilodefensin research 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Publication of our paper on earthworm drilodefensins led to substantial public interest. This included newspaper articles in the national and international press (including The Guardian, the Financial Times, the Washington Post, and Le Figaro), television interviews (for London-area local news), and radio interviews (for national and local radio, including BBC Scotland).
Year(s) Of Engagement Activity 2015
URL https://nature.altmetric.com/details/4361277