龜山島淺海熱泉怪方蟹的硫化氫轉換與後續運輸機制研究

Abstract

海底熱泉旁通常具有高濃度硫化氫釋放，而硫化氫會抑制生物的呼吸代謝，進而限制生物的生存。在此環境生存的生物，諸如深海熱泉中的螃蟹、貽貝、鬚腕類生物已知具備特殊的細胞解硫機制。然而，龜山島周遭的淺海熱泉組成，有別於典型的海底熱泉系統，在此區域棲息的硫磺怪方蟹(Xenograpsus testudinatus)對硫化物的耐受與適應機制，亦多屬推測並缺乏系統性的探討。 本論文研究目的旨在瞭解硫磺怪方蟹在其原生高硫環境是如何有效地進行硫化氫相關的解毒機制。實驗結果發現：怪方蟹血液具有亞磺酸(hypotaurine)與硫代牛磺酸(thiotaurine)的存在；在高硫環境中，怪方蟹第三、五對鰓的牛磺酸運輸蛋白(taurine transporter, TAUT，可運輸taurine、hypotaurine、thiotaurine)之表現量明顯高於無硫環境馴養的個體。以上結果皆暗示怪方蟹可能具備將S2-與hypotaurine代謝生合成thiotaurine，以降低硫毒性再進行運輸的適應能力。此外，本研究亦發現在原生高硫環境生存的怪方蟹鰓中，與硫運輸相關的表皮膜蛋白solute carrier family 26 member 11 (SLC26A11)基因與蛋白表現量均顯著高於無硫馴養的實驗個體。此結果暗示硫化氫氧化後形成毒性較低的硫酸根產物，可藉由鰓表皮細胞底膜的SLC26A11將硫酸根離子運輸至血液。根據以上結果我們推論：硫磺怪方蟹具有特殊的硫轉換機制，並在其鰓表皮上具有專一的硫相關運輸蛋白，可有效地降低生存在高硫環境中持續存在的毒性緊迫，以利在熱泉環境中生存。

The shallow-water hydrothermal vent system of Kueishan Island off the coast of Taiwan has been described as one of the most acidic vents in the world, discharging water with a high content of sulfur compounds. Sulfide is an inhibitor of cytochrome oxidase activity thus abolishes aerobic respiration. To survive in this toxic habitats, the vent crab, Xenograpsus testudinatus, may show a range of physiological feature to cope with sulfide-rich environment. In this study, we found the presence of hypotaurine and thiotaurine in the hemolymph, and transcript expressions of taurine transporter (taut) in the 3rd and 5th gill pair are significantly higher in native sulfidic environment than in non-sulfide treated seawater. Protein expression of TAUT in the 5th pair gill showed the similar appearance. These results inferred that X. testudinatus gills are capable to catabolize hypotaurine and S2- thus synthesize thiotaurine to reduce cellular toxicity. In addition, highly expressions of sulfur transport-related solute carrier 26A11 (SLC26A11), was found in gills of native habitants. It implies that sulfide may be oxidized to sulfate then transported by SLC26A11 in gill epithelium. Accordingly, X. testudinatus have evolved efficient sulfide detoxification mechanisms in gill epithelium to minimize sulfide-induced toxic stress under hydrothermal vent system.