Goffredi S K, Childress J J, Desaulniers N T, Lallier F J
Marine Science Institute, University of California, Santa Barbara, CA 93106, USA.
J Exp Biol. 1997 Oct;200(Pt 20):2609-16. doi: 10.1242/jeb.200.20.2609.
Deep-sea hydrothermal vents are home to a variety of invertebrate species, many of which host chemosynthetic bacteria in unusual symbiotic arrangements. The vent tubeworm Riftia pachyptila (Vestimentifera) relies upon internal chemolithoautotrophic bacterial symbionts to support its large size and high growth rates. Because of this, R. pachyptila must supply sulfide to the bacteria, which are far removed from the external medium. Internal H2S ([H2S+HS-+S2-]) can reach very high levels in R. pachyptila (2-12mmoll-1 in the vascular blood), most of which is bound to extracellular hemoglobins. The animal can potentially take up sulfide from the environment via H2S diffusion or via mediated uptake of HS-, or both. It was expected that H2S diffusion would be the primary sulfide acquisition mechanism, paralleling the previously demonstrated preferential uptake of CO2. Our data show, however, that the uptake of HS- is the primary mechanism used by R. pachyptila to obtain sulfide and that H2S diffusion into the worm apparently proceeds at a much slower rate than expected. This unusual mechanism may have evolved because HS- is less toxic than H2S and because HS- uptake decouples sulfide and inorganic carbon acquisition. The latter occurs via the diffusion of CO2 at very high rates due to the maintenance of an alkaline extracellular fluid pH. H2S accumulation is limited, however, to sulfide that can be bound by the hemoglobins, protecting the animal from sulfide toxicity and the symbionts from sulfide inhibition of carbon fixation.
深海热液喷口是多种无脊椎动物物种的栖息地，其中许多物种以不同寻常的共生方式容纳着化能合成细菌。喷口管虫厚壳贻贝（Vestimentifera）依靠其体内的化能无机自养细菌共生体来维持其庞大的体型和高生长速率。正因如此，厚壳贻贝必须向远离外部介质的细菌供应硫化物。在厚壳贻贝体内，内部硫化氢（[H₂S + HS⁻ + S²⁻]）可达到很高的水平（血管血液中为2 - 12 mmol·l⁻¹），其中大部分与细胞外血红蛋白结合。这种动物可能通过H₂S扩散或通过介导的HS⁻摄取，或者两者兼而有之，从环境中摄取硫化物。预计H₂S扩散将是主要的硫化物获取机制，这与先前证明的对CO₂的优先摄取情况类似。然而，我们的数据表明，HS⁻的摄取是厚壳贻贝获取硫化物的主要机制，而且H₂S向虫体内的扩散显然比预期的要慢得多。这种不同寻常的机制可能已经进化出来，因为HS⁻的毒性比H₂S小，而且HS⁻的摄取使硫化物和无机碳的获取解耦。后者是由于维持碱性细胞外液pH值而通过CO₂的高速扩散发生的。然而，H₂S的积累仅限于能够被血红蛋白结合的硫化物，从而保护动物免受硫化物毒性的影响，并保护共生体免受硫化物对碳固定的抑制。
