|Olavius algarvensis symbiont metaproteome|
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The marine oligochaete worm Olavius algarvensis lacks both a digestive and an excretory system, relying instead on a symbiotic community of two gammaproteobacterial sulfur oxidizers and two deltaproteobacterial sulfate reducers. A metagenomic analysis yielded many novel insights into the metabolic potential of the symbionts and generated many hypotheses on how the symbionts support the host through recycling of waste products and de novo generation of organic compounds via autotrophy. However, many questions regarding how this symbiosis successfully thrives in its extremely nutrient and energy poor environment, were left unanswered.
Therfore we used cultivation independent methods - metaproteomics and metabolomics - to study the symbionts' and the host's metabolism under natural conditions. Using both gel-free and gel-based methods and density gradient centrifugation to enrich for each of the four symbionts, we were able to identify and relatively quantify 2289 symbiont proteins. Despite the lack of a genome sequence from O. algarvensis or any other gutless oligochaete, we were also able to identify 530 host proteins by cross species protein identification using genomes from related invertebrates. Additionally, we were able to identify and relatively quantify 97 metabolites. This combined metaproteomic and metabolomic study revealed novel insights into the O. algarvensis symbiosis including unusual pathways for energy conservation and the fixation of inorganic carbon.