Published online 16 December 2008 | Nature | doi:10.1038/news.2008.1309

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The year of the worm?

The earthworm is finally inching its way into the genomic age.

EarthwormThe draft genome of the earthworm is expected next year.Punchstock

Interest in the humble earthworm seems to have seen a revival of late. Stephen Stürzenbaum from Kings College London and his team are hoping to unveil its draft genome next year, and Stürzenbaum tells Nature News why he has written a review on the topic for Proceedings of the Royal Society B1.

What was the motivation behind this paper?

When I started my PhD my, if you want, claim to fame was to be one of the first to do some molecular genetics on earthworms. With time more people have done it and now we've changed the earthworm from being a sentinel soil organism that is used for eco-toxicology studies to an organism with some genetic data.

Next year is Charles Darwin's [200th] birthday, and as Darwin was a fellow of the Royal Society — one of the 'old, clever guys' — we thought a review in a Royal Society journal would beautifully complement his [last] work, [on earthworms]2.

Do you feel that the earthworm has been neglected in preference to say, the roundworm Caenorhabditis elegans?

It's all down to who you talk to. If you talk to a soil biologist or an eco-toxicologist, they would immediately say 'yes, we know a lot about the earthworm, we've done a lot with it, it's a useful organism, an essential organism'. However, if you talk to a C. elegans person they would immediately say from a model organism point of view the earthworm is totally neglected.

Drosophila and C. elegans are fantastic organisms that are used a lot — beautiful genetic tools. However in terms of biological relevance there's a question mark. Not biology as in human biology, there's enough evidence to link C. elegans to human disease. However, 'true' biology, as in animal biology. There scientists from the earthworm community would say that C. elegans is a lab rat, nothing else.

Why do you say in your paper that the earthworm could become a "genetic model organism" for environmental soil science?

Punch caricature of DarwinPunch Magazine played on Darwin's links with worms in this famous 1882 caricature.Punch

The earthworm has been used for toxicity testing but up until now researchers used a bucket and spade approach. You'd take some soil, put some earthworms in and count how many died to determine the LC50 [the concentration at which 50% of the organisms die]. There you are —that's what we know. However by determining the genetic basis of the earthworm we can now devise more refined testing.

Having said that, if you look at gene conservation, an earthworm is closer to a human than C. elegans is. So Darwin was right: 'man is but a worm'.

So what will the draft sequence bring?

We're sequencing like mad. So far we've got about 1.5x coverage of the genome. We're aiming for up to five-fold coverage.

Currently a worm biologist will look at an worm and say yes it is Lumbricus rubellus, Lumbricus terrestris, or whatever. However we're finding that – and these are unpublished results – that there are cryptic species [species that seem identical but are genetically unique], and that some lineages are resistant to pollution whereas others aren't.

So if we're to do a tox-test and randomly pick worms and test them and by chance pick the wrong lineage we could over- or underestimate toxicity. We need good genetic information. 

  • References

    1. Stürzenbaum, S. R., Andre, J., Kille, P., & Morgan, A. J. Proc. R. Soc. B doi:10.1098/rspb.2008.1510 (2008).
    2. Darwin, C. The Formation of Vegetable Mould Through the Action of Worms With Observations on Their Habits (1891).
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