The sulfide this worm needs is created by a consortium of bacteria and archaea that live in the deep sea cold sediments surrounding the seep where the worm lives. These chemoautotrophs use energy from hydrocarbons to reduce sulfate to sulfide, which L. luymesi absorbs through its unique "roots," extensions of its body that it tunnels into the sediments. However, current measurements of sulfide and sulfate fluxes in the water near the vents do not match the observed tubeworm colony size and individual longevity, leading Cordes et al. to propose that L. luymesi also uses its roots to release sulfate back to the microbial consortia from which it draws its sulfide. Without this return of sulfate, the model predicts an average lifespan of only 39 years in a colony of 1,000 individuals; with it, survival increases to over 250 years, matching the longevity of actual living tubeworms.
To date, the proposed return of sulfate to the sediments through the roots is only a hypothesis--albeit one with much to support it--that still awaits direct confirmation. By providing a model in which this hypothetical interaction provides real benefits and explains real observations, the authors hope to stimulate further research into the biology of the enigmatic and beautiful L. luymesi.
Citation: Cordes EE, Arthur MA, Shea K, Arvidson RS, Fisher CR (2005) Modeling the mutualistic interactions betw een tubeworms and microbial consortia. PLoS Biol 3(3): e77.