Dattagupta Sharmishtha, Miles Lara L, Barnabei Matthew S, Fisher Charles R
Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA.
J Exp Biol. 2006 Oct;209(Pt 19):3795-805. doi: 10.1242/jeb.02413.
Lamellibrachia luymesi (Polychaeta, Siboglinidae) is a deep-sea vestimentiferan tubeworm that forms large bush-like aggregations at hydrocarbon seeps in the Gulf of Mexico. Like all vestimentiferans, L. luymesi obtains its nutrition from sulfide-oxidizing endosymbiotic bacteria, which it houses in an internal organ called the trophosome. This tubeworm has a lifespan of over 170 years and its survival is contingent upon the availability of sulfide during this long period. In sediments underlying L. luymesi aggregations, microbes produce sulfide by coupling sulfate reduction with hydrocarbon oxidation. L. luymesi acquires sulfide from the sediment using a root-like posterior extension of its body that is buried in the sediment. Its symbionts then oxidize the sulfide to produce energy for carbon fixation, and release sulfate and hydrogen ions as byproducts. It is critical for the tubeworm to eliminate these waste ions, and it could do so either across its vascular plume or across its root. In this study, we measured sulfate and proton elimination rates from live L. luymesi and found that they eliminated approximately 85% of the sulfate produced by sulfide oxidation, and approximately 67% of the protons produced by various metabolic processes, across their roots. On the basis of experiments using membrane transport inhibitors, we suggest that L. luymesi has anion exchangers that mediate sulfate elimination coupled with bicarbonate uptake. Roots could be the ideal exchange surface for eliminating sulfate and hydrogen ions for two reasons. First, these ions might be eliminated across the root epithelium using facilitated diffusion, which is energetically economical. Second, sulfate and hydrogen ions are substrates for bacterial sulfate reduction, and supplying these ions into the sediment might help ensure a sustained sulfide supply for L. luymesi over its entire lifespan.
鲁氏管栖蠕虫（多毛纲，西伯加林虫科）是一种深海须腕动物管虫，在墨西哥湾的碳氢化合物渗漏处形成大型灌木状群体。与所有须腕动物一样，鲁氏管栖蠕虫从硫化物氧化内共生细菌中获取营养，这些细菌存在于一个名为营养体的内部器官中。这种管虫的寿命超过170年，其生存取决于这一漫长时期内硫化物的可获得性。在鲁氏管栖蠕虫群体下方的沉积物中，微生物通过将硫酸盐还原与碳氢化合物氧化耦合来产生硫化物。鲁氏管栖蠕虫利用其埋在沉积物中的身体后部的根状延伸从沉积物中获取硫化物。然后，其共生体将硫化物氧化以产生能量用于碳固定，并释放硫酸盐和氢离子作为副产品。对于管虫来说，消除这些废物离子至关重要，它可以通过其血管羽或根部来做到这一点。在这项研究中，我们测量了活的鲁氏管栖蠕虫的硫酸盐和质子消除率，发现它们通过根部消除了大约85%的由硫化物氧化产生的硫酸盐，以及大约67%的由各种代谢过程产生的质子。基于使用膜转运抑制剂的实验，我们认为鲁氏管栖蠕虫有阴离子交换器介导硫酸盐消除并伴有碳酸氢盐摄取。根部可能是消除硫酸盐和氢离子的理想交换表面，原因有两个。首先，这些离子可能通过易化扩散穿过根上皮被消除，这在能量上是经济的。其次，硫酸盐和氢离子是细菌硫酸盐还原的底物，将这些离子供应到沉积物中可能有助于确保鲁氏管栖蠕虫在其整个寿命期间持续获得硫化物供应。
