Meeting Abstract

29.5  Friday, Jan. 4  Drilling for nutrition: The physiological mechanism of bone penetration by Osedax KATZ, S.*; TRESGUERRES, M.; ROUSE, G.W.; Scripps Institution of Oceanography, UCSD, San Diego; Scripps Institution of Oceanography, UCSD, San Diego; Scripps Institution of Oceanography, UCSD, San Diego skatz@ucsd.edu

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 also confirms this pattern. 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.