Ultrastructural reinvestigation of the trophosome in adults of Riftia pachyptila (Annelida, Siboglinidae)

Abstract

The trophosome of adults of Rifia pachyptila (Vestimentifera) was reinvestigated using 3-dimensional ultrastructural reconstruction and quantitative morphological analysis. The symbionts make up 24.1 %, the symbiont-containing cells (bacteriocytes) are 70.5% of the trophosome's volume. The trophosome is composed of lobules that have a central axial blood vessel surrounded by a myoepitheiium containing bacteriocytes, in turn surrounded by an apolar tissue of bacteriocytes. Part of the splanchnic peritoneum lining the trunk coelom encases the bacteriocytes and forms a ramifying network of peripheral blood vessels. Based on the morphology and ultrastructure of the adult, we hypothesize a mesodermal rather than endodermal origin of trophosome and its constitute bacteriocytes. Some of the central bacteriocytes are part of the myoepithelium surrounding the axial blood vessel and act as stem cells for a proliferating tissue produced in the center and ultimately degraded at the periphery of each lobule. Similarly, the rod-shaped symbionts in the center act as stem cells and exhibit a simple cell cycle. Differentiation into cocci takes place in the median and peripheral zone. Lysis of cocci occurs in the degenerative zone.

“CandidatusThiobios zoothamnicoli,” an Ectosymbiotic Bacterium Covering the Giant Marine CiliateZoothamnium niveum

“…Transitions from rods to coccoid shapes are usually accompanied by changes in cell size, whereby either morphotype can be larger than the other. In the growth cycle of A. globiformis, for example, irregular rods in young cultures are replaced by smaller coccoid forms in older cultures (51), whereas the chemoautotrophic thiotrophic endosymbiont of the tubeworm Riftia pachyptila is rod shaped and changes by terminal differentiation into larger cocci, showing transitional stages between the two morphotypes (8,9), similar to the morphological stages observed for the Z. niveum ectosymbionts analyzed in this study.…”

Physiological homogeneity among the endosymbionts of Riftia pachyptila and Tevnia jerichonana revealed by proteogenomics

“…While relatively little is known about T. jerichonana and its symbionts, the Riftia symbiosis has been studied extensively in the past: adult worms lack a mouth and digestive tract (Jones, 1981b) and are therefore completely dependent on the symbionts, which were taxonomically classified as Gammaproteobacteria . Substrates for bacterial chemosynthesis, that is, oxygen, sulfide and carbon dioxide, are taken up from the diffuse flow fluids through the worm's plume and delivered to the symbionts, which are enclosed in specialized host cells (bacteriocytes) in an organ termed trophosome (Hand, 1987;Bright and Sorgo, 2003). Bacterial sulfide oxidation provides the energy that fuels CO 2 fixation into organic matter (Cavanaugh et al, 1981;Felbeck, 1981;Felbeck and Somero, 1982;Fisher and Childress, 1984;Childress et al, 1991;Girguis and Childress, 2006).…”

Identification and classification of the principal microflora of the sea pineapple Halocynthia roretzi using MALDI biotyping and 16S rRNA analysis

“…in Riftia pachy ptila (Cavanaugh et al 1981, Bright & Sorgo 2003, Olavius algarvensis (Dubilier et al 2001, Rueh land et al 2008, sponges (Vacelet & Donadey 1977, Friedrich et al 1999, molluscs (Kimbell & McFall-Ngai 2003, McFallNgai et al 2010, clams (Fisher 1990, Newton et al 2007, Southward 2009) and mussels (Distel & Cavanaugh 1994, Duperron et al 2009). The diversity of these associations is very broad, and there are still many questions about the origin and the exact relationship between the host and its symbionts.…”