An autoradiographic examination of carbon fixation, transfer and utilization in the Riftia pachyptila symbiosis

Riftia pachyptila, the giant vestimentiferan tubeworm from the East Pacific Rise, harbors abundant chemolithoautotrophic, sulfide-oxidizing bacteria in an internal organ, the trophosome. Several facts, such as the lack of a digestive system in the host, stable carbon isotope values and net carbon dioxide uptake all suggest that the tubeworms obtain the bulk of their nutrition from their symbionts. Using tissue autoradiography, we investigated the mode of nutritional transfer between symbionts and host, and the site of early incorporation of symbiont fixed-carbon in the host. Fast labeling in the trophosome clearly demonstrates that the symbionts are the primary site of carbon fixation. Appearance of label in some symbiont-free host tissues in as little as 15 min indicates that the symbionts release a significant amount of organic carbon immediately after fixation. The organic carbon is largely incorporated into specific, metabolically active host tissues such as fast-growing body regions in the trunk and plume, and into tube-secreting glands. In addition to immediate release of fixed carbon by the symbionts, there is evidence of a second possible nutritional mode, digestion of the symbionts, which is consistent with previous suggestions based on trophosome ultrastructure. Results suggest that symbiont-containing host cells migrate in a predictable pattern within trophosome lobules and that symbiont division occurs predominately in the center of a lobule, followed eventually by autolysis/digestion at the periphery of the lobule. Received: 1 July 1999 / Accepted: 30 December 1999     

The sensitive and selective determination of aluminium by spectrofluorimetric detection after complexation with N-o-vanillidine-2-amino-p-cresol

A simple, easy to use and selective spectrofluorimetric method for the determination of trace levels of aluminium has been developed. A new Schiff base, N-o-vanillidine-2-amino-p-cresol (OVAC), has been synthesized and its fluorescence activity with aluminium investigated. Based on this chelation reaction, a spectrofluorimetric method has been developed for the determination of aluminium in samples buffered at pH 4.0 using acetic acid-sodium acetate. The chelation reaction between Al(iii) and N-o-vanillidine-2-amino-p-cresol was very fast, requiring only 20 min at room temperature to complex completely. The excitation and emission wavelengths were 423.0 and 553.0 nm, respectively, at which the OVAC-Al complex gave the maximum fluorescence intensity at pH 4.0 in a 50% ethanol-50% water medium. The interference from fluoride ions was minimized by the addition of Be(2+). Other ions were found not to interfere at the concentrations likely to be found in natural waters. Under these conditions, the calibration plot was linear up to 1000 microg L(-1) (r = 0.999). The limit of detection (3sigma) for the determination of Al(iii) was 0.19 microg L(-1) and the precision for multiple determinations of 3 ng mL(-1) Al(iii) prepared in ultra-pure water was found to be 0.29% (n = 16). The Schiff base ligand could be used to determine ultra-trace aluminium from natural waters. Analysis of environmental certified reference materials showed good agreement with the certified values. The procedure was found to be equally applicable to both fresh water and saline solutions (including sea water) using either normal external calibration or the standard additions method.     

Methane Ice Worms: Hesiocaeca methanicola Colonizing Fossil Fuel Reserves

 During a research cruise in July 1997 in the Gulf of Mexico we discovered a gas hydrate approximately 1 m thick and over 2 m in diameter which had recently breached the sea floor at a depth of 540 m. The hydrate surface visible from the submarine was considerably greater than that of any other reported hydrate. Two distinct color bands of hydrate were present in the same mound, and the entire exposed surface of the hydrate was infested (2500 individuals/m²) with 2 to 4 cm-long worms, since described as a new species, Hesiocaeca methanicola, in the polychaete family Hesionidae (Desbruyères and Toulmond 1998). H. methanicola tissue stable isotope values are consistent with a chemoautotrophic food source. No evidence of chemoautotrophic symbionts was detected, but geochemical data support the presence of abundant free living bacteria on the hydrate. The activities of the polychaetes, grazing on the hydrate bacteria and supplying oxygen to their habitats, appears to contribute to the dissolution of hydrates in surface sediments. Received: 16 August 1999 / Accepted in revised form: 19 January 2000     

An economic model of the US aluminium market

An economic model of the US aluminium industry is constructed and estimated with annual data over the period 1960–1978. The authors' analysis shows that both the short- and long-term price elasticities of demand are relatively low, and that demand is highly dependent on aluminium end-use activity. A forecasting exercise is also undertaken, and the errors of forecast calculated.     

Translocation of fixed carbon from symbiotic bacteria to host tissues in the gutless bivalve Solemya reidi

Naturally-occurring lipophilic inducers of larval settlement and metamorphosis wer isolated and identified for Phragmatopoma californica, a gregarious tube worm from southern California. Organic solvent extraction of the sand/organic cement matrix of tubes diminished the inducing capacity of the tube matrix. The inducing capacity was restricted to a single, highly active, HPLC-purified fraction of the organic solvent extract. Chemical analysis of this fraction revealed a mixture of free fatty acids (FFAs), dominated by eicosapentaenoic acid (20:5, 20%), palmitic acid (16:0, 14%) and palmitoleic acid (16:1, 12%). In assays of the nine FFAs that each contributed 3% or more to the active fraction, only 16:1, 18:2, 20:4 and 20:5 induced larval settlement and metamorphosis, while the others were ineffective. The larval response was contact-dependent, highly specific, and concentration-dependent, with a significant response to 16:1 and 20:4 at as low as 10 g FFA spread onto 1 g of sand (surface area 36 cm²). Active FFAs were extracted at approximately 14 g g^-1 sand from the tube matrix, although the levels encountered by larvae in nature are believed to be higher.