"Dissolving" a hard problem: Osedax’s way of bone penetration

Annelids belonging to Siboglinidae lack a gut and obtain nutrition via bacterial symbionts housed in a specialized organ called the trophosome. While most siboglinids host chemoautotrophic symbionts, which allow them to thrive in reducing habitats such as hydrothermal vents or methane seeps, Osedax exploits vertebrate bones lying on the seafloor. Furthermore in contrast to other siboglinids, Osedax house heterotrophic Oceanospirillales bacteria in their posterior body, which is modified into so-called ‘roots’. These roots penetrate and ramify through the bone, which serves as their food source (Goffredi et al., 2007). However, Osedax lack any obviously bioabrasive structures and the physiological mechanism of bone erosion and nutrient absorption has been virtually unknown. The ultrastructure of the root epidermis suggests secretory/absorptive functions of this region and we hypothesized Osedax demineralize the bone by secreting acid, followed by absorption of bone collagen and lipids for nutrition. Our analysis of putative acid-secreting proteins, namely vacuolar H+-ATPase (VHA) and carbonic anhydrase (CA), by immunohistochemistry and quantitative immunoblotting, shows preferential location and high abundance of VHA in the root epidermal cells. Analysis of transcriptome data of the root vs. the trunk region revealed intra- and extracellular carbonic anhydrases and several subunits of VHA. They were significantly higher expressed in the roots compared to trunk (VHA subunit A 2.5-fold, VHA subunit B 5-fold, 3 different forms of CA 100- to 500-fold). CA is co-occuring with VHA in the root epidermis, and additionally found in other cells and body regions, suggesting CA is also involved in maintaining acid/base balance throughout the worm. These results support our hypothesis on bone erosion via acid secretion by Osedax, which is similar to chemical mechanisms employed for boring by some gastropods and for bone demineralization by human osteoclasts.

Your format preference:: 
Oral Presentation
Would you be interested in publishing this conference paper in a special issue of Marine Ecology?: 
No
First Name: 
Sigrid
Last Name: 
Katz
Telephone: 
+1 (858) 990 4383
Affiliation: 
Scripps Institution of Oceanography, University of California San Diego
First Name: 
Martin
Last Name: 
Tresguerres
Affiliation: 
Scripps Institution of Oceanography, University of California San Diego
First Name: 
Greg W.
Last Name: 
Rouse
Affiliation: 
Scripps Institution of Oceanography, University of California San Diego
Choose keywords that are most applicable to your abstract. (Three maximum.): 
Trophic relations (including symbiosis)
Physiology
Abstract ID: 
CBE5-143