Coexistense of multiple endosysmbionts in the tubeworm Lamellibrachia satsuma revealed by comparative metagenomic analysis

Abstract

Lamellibrachia satsuma is a small vestimentiferan tubeworm, one of the common members of faunal communities in the Kagosima Bay. These tubeworms are nourished by bacterial endosymbionts growing in a specialized tissue called the trophosome. Two samples from different cluster of Lamellibrachia satsuma of the seep were studied. Metagenomic library were constructed using Illumina HiSeq 2000 platform from the trophosome. Comparative metagenomics analysis carried out with the data annotated from MG-RAST by STAMP software. The analysis suggest that the tubeworm harbor mostly γ-proteobacterial endosymbiont in all tubeworms irrespective of different location, but in one sample, presence of &#61541 -proteobacterial endosymbiont provide a new direction regarding acquisition of endosymbiont by the tubeworm based on different geographical location and environmental microflora surrounding the vestimentiferan habitat. The endosymbionts contain all genes required for oxidizing reduced sulfur compounds (H2S to SO4) mediated through the cytoplasmic enzyme adenylylsulfate reductase (AprA/AprB). The endosymbiont harbors genes for two different carbon fixation pathways, the Calvin cycle as well as the rTCA cycle, as has been reported in the endosymbiont of the various tubeworms of vent and seep communities. This study suggests that, endosymbiont uptake inorganic material supplied by tubeworm and transform in to organic compounds which fulfil the energy requirement of the tube worm despite of presence of different class of endosymbionts. Studying the role of coexisting endosymbionts from the metagenome is still a challenge, which is yet to be studied.