Wissenschaft
Using a marine annelid worm as a tiny model of outsourcing
Olavius algarvensis feels most at home in the sandy sea beds surrounding the Mediterranean island Elba and has been a subject of research for some time –. at the Max-Planck Institute (MPI) for Marine Microbiology in Bremen. The tiny annelid worm is of interest most of all because it neither possesses a mouth, intestines, a stomach, nor kidney-like organs. For food intake and waste disposal, it uses bacteria, for which it plays the role of landlord. As the Bremen-based scientists recently reported in Nature magazine, the genomes of four of the symbiotic bacteria from the inside of the worm have been decoded.
To decode the hereditary properties behind such an intense partnership, and to assign the individual, mixed sequences to each particular organism gave the scientists an extremely difficult task. The main problem is that the scientists cannot let the symbiotic microorganisms grow individually. Therefore they have fallen back on metagenome analysis with which individual genomes are decoded without needing to isolate the respective organism.
New procedure for metagenome analysis
But the classical procedures employed in genome analysis cannot simply be used in metagenome analysis. Much like a collection of mixed texts by different authors, the individual passages must be assigned to the correct author. In order to guarantee that this is achieved without error, Hanno Teeling, a German researcher at the MPI for Marine Microbiology, has developed a new mathematical algorithm, called the Binning procedure. It is based on the assumption that the succession patterns of the individual DNA components differ from organism to organism. From the frequency of certain combinations, it is possible to reconstruct individual fragments in sub-groups (Bins), and for these to be reconstructed again in individual genomes. With this, the researchers in Bremen have found the key for a more detailed analysis of the symbioses underlying Olavius algarvensis.
Outsourcing experts as model for space research
The tiny worm is an annelid worm (class: oligochaete) which is settled by lots of microorganisms, partaking in a symbiotic relationship with their host. As is the case with many other symbioses, the worm has thereby greatly reduced its digestion system, and the functions of mouth, stomach and intestines have been taken over by the symbiotic bacteria. However, Olavius algarvensis takes its outsourcing strategy to the limits, as it doesn’t even possess kidney-like organs, the so-called nephridia. All processes to do with food intake and waste disposal are delegated entirely. Thus, Olavius algarvensis is a highly interesting model as an almost entirely self-sufficient mini biosphere. Research into larger comparable systems is being informed by these insights, for instance, the longer space flights that will be necessary if man is to travel to other planets like Mars.
Landlord-symbiont relations efficient over the smallest areas
As the German MPI Symbiosis researcher group under Nicole Dubilier, together with their US-American colleagues at the Joint Genome Institute (JGI), have reported in Nature magazine (online publication, 17 September), four bacteria can be found working together in Olavius algarvensis: two sulfur bacteria (Gammaproteobacterium) and two sulfate reducers (Deltaproteobacterium). Using metagenome analysis, the researchers were able to reconstruct the respective metabolisms of the individual organisms and, with this, uncover which methods were employed by the bacteria depended on the environmental Influences. It turned out that the worm, with its symbionts, possesses a form of mini power station, which operates for the mutual advantage for everybody involved. The sulfate-reducing bacteria produces reduced sulfur connections for example, which the sulfur-oxidizing bacteria can then use again as an energy source. Thus, the symbionts feed themselves, and each other. Surprisingly, the researchers also stated that all four of the worm’s symbionts, like plants, can absorb carbon dioxide, as well as decomposing poisonous metabolic products, such as urea and ammonium.
In this way, they contribute to the recycling of valuable nitrogen. What is more, the worm ensures for the fact that, in each case, the various bacteria are exposed to an optimal energy input, by moving between upper (oxygen-rich) and lower (oxygen-poor) coastal sediments. "The small worm Is an Ideal modell for the efficient use of limited resources by cooperating with and coordinating microbial communities over a tiny area ", says Nicole Dubilier, summarizing the results. Other not-yet-published studies have also discovered that the sulfate-reducing bacteria discovered in Olavius algarvensis also clearly appear as symbionts in other gutless worms, and thereby possibly play a substantial role in the outsourcing strategy of these marine host organisms.
