Pity the poor worm; struggle for Phylum Annelida survival more complex than previously thought

By Nicolette Smith - 07 Mar 2011 14:4:0 GMT
Pity the poor worm; struggle for Phylum Annelida survival more complex than previously thought

What sort of personality traits do you associate with worms? Presumably not 'risk-takers', gamblers' or 'adrenaline junkies'? Not many people would confess to an admiration for the worm species, and yet a recent study backed by the Biotechnology and Biological Sciences Research Council (BBSRC) has shown that worms are the ultimate gamblers; a type of worm known as a Nematode plays a high-risk game…with disease resistance.

The Nematode or 'Roundworm' variety of worm – a creature less than 2mm in length – is faced with the ultimate survival choice: it must choose bacterial immunity to one microbial infection over and above another which also poses a physiological threat. Nematodes build a 'made to order' immune system; a high-risk strategy which leaves them extremely vulnerable to disease. The precarious nature of life as a worm had not previously been recognised, and the new study, which was published in the Journal PLoS ONE Today, has brought a whole new realm of understanding to the much-underestimated worm family.

Dr Robin May, who organised the research, emphasised the complex survivalist instinct of the worm’s immune system: ''This finding was a real surprise. These worms have quite a simple immune system, so when we deleted a gene which we already knew provided resistance to a type of fungus; we were amazed to find that the worms became more resistant to Salmonella bacteria. It seems that evolving resistance to the fungus came at the cost of making the worms more vulnerable to other diseases.''

Dr May went on to explain: ''Whilst scientists have seen this phenomenon, where there is a see-saw balance between immunity to different diseases, in more complex animals before, it has never been shown in anything as simple as a nematode worm. We think that this phenomenon evolved separately in C. elegans indicating that this trade-off is important across the animal kingdom.''

Managing an immune system is something which we generally take for granted, but for an animal it monopolises rather a lot of physical energy. The physical cost associated with this general maintenance can be great, and can considerably weaken the animal's strength. In order to prevent this associated weakness, many animals carry out some form of 'cost'/'benefit' analysis, whereby the constant maintenance of the immune system weakens the animal and increases its vulnerability to certain diseases. It really is a case of 'out of the frying pan, into the fire.'

The study showed that Nemotodes reduced their resistance to Salmonella as an immune system 'sacrifice', and in return their immune response to Cryptococcus was fortified. Researchers removed a gene from the worm, Lys-7, a gene which actively reduces microbes via the production of lysozymes (enzymes which break down bacterial cell walls). Dr May emphasised the utility of the research:''We're not quite sure why losing this lysozyme makes the worms better equipped to fight off Salmonella. One possibility is that losing the gene gives other parts of immune system a boost, or perhaps Salmonella normally turns on its defence mechanisms in response to the presence of this lysozyme.''

Whatever the reason, the study has shed new light on our auto-immune response to hostile bacterial infections; the fungal infection Cryptcoccus Neomans is a pathogen which adversely affects humans suffering from diseases such as AIDs, in which the immune response has been weakened. The Chief Executive of the BBSRC, Douglas Kell, had this to say of the wide-reachinng implications of the study's findings: ''Understanding how the immune system works and how it has evolved in different animals will be important in dealing with a number challenges facing society, from chronic inflammation reducing people's quality of life in old age, to crop pests developing resistance to pesticides.''

Whatever the implications, the study has brought about a new-found respect for the little worm.