1. DOE Joint Genome Institute, Walnut Creek, California 94598, USA
2. Lawrence Berkeley National Laboratory, Genomics Division, Berkeley, California 94720, USA
3. Max Planck Institute for Marine Microbiology, 28359 Bremen, Germany
4. International University Bremen, 28759 Bremen, Germany

Correspondence to: Edward M. Rubin^1,2Nicole Dubilier³ Correspondence and requests for materials should be addressed to N.D. (Email: ndubilie@mpi-bremen.de) or E.M.R. (Email: EMRubin@lbl.gov). The assembled sequences from the Olavius symbionts' metagenome have been deposited into the NCBI database under the project accession number AASZ00000000. The annotated Olavius symbionts' bins were incorporated into the metagenomics version of the US Department of Energy Joint Genome Institute Integrated Microbial Genomes/M (IMG/M; http://img.jgi.doe.gov/mS).

Abstract

Symbioses between bacteria and eukaryotes are ubiquitous, yet our understanding of the interactions driving these associations is hampered by our inability to cultivate most host-associated microbes. Here we use a metagenomic approach to describe four co-occurring symbionts from the marine oligochaete Olavius algarvensis, a worm lacking a mouth, gut and nephridia. Shotgun sequencing and metabolic pathway reconstruction revealed that the symbionts are sulphur-oxidizing and sulphate-reducing bacteria, all of which are capable of carbon fixation, thus providing the host with multiple sources of nutrition. Molecular evidence for the uptake and recycling of worm waste products by the symbionts suggests how the worm could eliminate its excretory system, an adaptation unique among annelid worms. We propose a model that describes how the versatile metabolism within this symbiotic consortium provides the host with an optimal energy supply as it shuttles between the upper oxic and lower anoxic coastal sediments that it inhabits.

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