Effects of sulphide on anoxia-driven mortality and anaerobic metabolism in the ark shell Anadara kagoshimensis

Reduction in survival under hypoxic conditions in the presence of sulphide has been repeatedly demonstrated in various benthic invertebrates. However, the reason for this reduction has not yet been clearly elucidated. In this study, the effects of sulphide accumulation on anoxic survival and anaerobic metabolism were investigated in the ark shell Anadara kagoshimensis. Ark shells from western Japan were experimentally exposed to 3 sulphide-accumulation levels under sustained anoxic conditions: accumulated H2S treatment (static incubation), decreased H2S treatment (semi-static incubation with daily replacement of incubation media), and inhibited H2S treatment (static incubation with the addition of antibiotics). Moreover, the effect of antibiotics on anoxic survival was examined under sulphide exposure. The decreased H2S and inhibited H2S treatments resulted in 1.5- and 3-fold increase in the anoxic survival time, respectively, when compared with the accumulated H2S treatment. Under anoxic sulphide exposure, the antibiotics addition did not affect survival time, suggesting the shorter survival time in the accumulated H2S incubation was probably due to sulphide toxicity. Glycogen consumption and propionate accumulation, which indicate activation of anaerobic metabolism, were observed in both accumulated and inhibited H2S treatments. However, glycogen consumption was significantly higher in the accumulated H2S treatment after a significant sulphide accumulation was detected in the incubation media. In addition, survival in the accumulated H2S treatment decreased rapidly, whereas no significant mortality was observed in the inhibited H2S throughout the experiment. These results likely suggest that the accelerated anoxic-driven mortality in sulphide-rich environments was partly due to the faster breakdown of glycogen.

Ebselen Analogues Reduce 2-chloroethyl Ethyl Sulphide Toxicity in A-431 Cells

Vesicants are potent blistering agents. The prototype vesicant is sulphur mustard gas, first used in World War I, which still has no effective antidote. We used a mustard gas surrogate 2-chloroethyl ethyl sulphide (CEES) to study the ability of resveratrol (RES) and pterostilbene (PTS), two well-established stilbene antioxidants, ebselen (EB-1), an organoselenium compound, and three EB-1 analogues (EB-2, EB-3, and EB-4) to reduce CEES toxicity in human epidermoid carcinoma cells (A-431). Following a 24-hour incubation of a toxic concentration of CEES (1000 μmol L-1), we used the MTT [3-(4,5-dimethylthiazol- 2-yl)-2,5-diphenyltetrazolium bromide] test to analyse cell viability. Different concentrations of test antioxidants alone (15 μmol L-1, 30 μmol L-1 or 60 μmol L-1) did not decrease cell viability. Treatment with CEES and test antioxidants for 24 h showed that only EB-1 and its analogues EB-2, EB-3, and EB-4 but not the stilbene compounds could rescue the cells from death. EB-1 and EB-4 were the most effective at reducing CEES cytotoxicity and did so in a concentration-dependent manner, while EB-2 and EB-3 demonstrated the least protective effect. In summary, the data described herein indicate that organoselenium antioxidants, especially EB-4, may prove useful as countermeasures to blistering agents.

Role of physico-chemical environment on gastropod assemblages at hydrothermal vents on the East Pacific Rise (13°N/EPR)

Deep-sea hydrothermal vents display extreme and highly variable environmental conditions that are expected to be among the most important factors structuring associated benthic populations and communities. We tested this assumption, focusing on the distribution of gastropods, as well as on the demographic population structure and reproductive biology of one dominant gastropod species in zones characterized by alvinellid polychaetes and vestimentiferan tubeworms. A total of 14 biological samples from both types of habitats were collected at three sites on the East Pacific Rise 13°N vent field in May 2002. At all vents except one, the physico-chemical environment was described in two steps: (1) pH, total sulphide and reduced iron concentrations have been measuredin situinAlvinellahabitats and correlations to temperature were assessed at the scale of each sampled vent; and (2) assuming the consistency of these relationships within a single edifice, ranges of physico-chemical factors were estimated for each biological sample from the corresponding fine scale temperature measurements. A total of 11 gastropod species were identified from all samples and 2 main faunal assemblages were distinguished: one dominated byLepetodrilus elevatusin the alvinellid zone as well as in the vestimentiferan zone, and one dominated by the peltospiridsNodopelta heminoda, N. subnodaandPeltospira operculataconfined to the alvinellid zone. Peltospirid gastropods were dominant over lepetodrilid gastropods in the more acidic, sulphide-richer, and hotter environments. Although this pattern could be related to specific physiological tolerances to temperature and sulphide toxicity, the weak correlation between community structure and physico-chemical variables suggests that additional factors are also involved. Particularly, the low species richness and the overwhelming dominance ofL. elevatusin one faunal assemblage suggest that this species may outcompete peltospirids and greatly affect community structure. This hypothesis is supported by large differences in the demographic structure and reproductive biology ofL. elevatusbetween the 2 faunal assemblages.

Parasitism as a potential contributor to massive clam mortality at the Blake Ridge Diapir methane-hydrate seep

Vesicomyid clam species are abundant in many deep-sea chemosynthetic communities, including cold seeps. They rely primarily on thiotrophic (sulphide-oxidizing) gill symbionts for nutrition and thus require sulphide-rich environments. Submersible surveys of megafaunal distributions at the Blake Ridge Diapir, a deep-sea methane-hydrate seep located ∼200 miles off the coast of Charleston, South Carolina, documented massive mortalities of vesicomyid clams. The cause of these mortalities is unknown, but sulphide deprivation, sulphide toxicity, and disease are possible agents of mortality in this system. Similar redox profiles in sediment cores from live and dead clam beds do not support the hypothesis that there has been a transient shift in the flux of sulphide. To address the potential for disease as a cause of mortality, we undertook a histological survey of microparasites and other indications of disease in clam tissues. Six morphological types of parasites were identified using light microscopy, including two viral-like inclusions, Rickettsia-like gill inclusions, possible bacterial gut inclusions, bacterial gill infections, and a protistan inclusion. Of these parasites, two were pathogenic: viral-like inclusions in mantle tissues caused tissue degradation; bacterial gill infections resulted in localized disruption and degradation of gill filaments. Infection prevalence and densities were low for all parasites observed. The majority of clams examined showed intense haemocytic responses in the absence of any obvious etiologic agent, suggesting the presence of parasites not detectable by our methods. Our findings indicate that the clam population at the Blake Ridge seep was in relatively good health at the time of sampling.

Improvement of anaerobic treatment of tannery beamhouse wastewater by an integrated sulphide elimination process

Sulphide, and especially the undissociated form, hydrogen sulphide, is inhibitory to anaerobic wastewater treatment processes. Tannery beamhouse wastewater contains high concentrations of organic material which make an anaerobic treatment favourable, but it also contains high concentrations of sulphide which cause difficulties for anaerobic treatment. The success of an anaerobic treatment will depend on reliable elimination of the sulphide. In batch tests stripping was the most effective process for sulphide removal compared to precipitation. The chemical-physical COD removal caused by the stripping was negligible, while precipitation caused a COD-removal of 26%. Also, anaerobic degradation velocity was higher if sulphide was removed by stripping. In fixed bed reactors operated continuously, stripping was shown to be a reliable method for eliminating hydrogen sulphide toxicity. Hydrogen sulphide caused an inhibition of 0.2% per mg 1−1 for methanogenic bacteria. Acidogenic bacteria were not inhibited by hydrogen sulphide. The gas-liquid equilibrium was shown to deviate from theoretical values taken from literature.