Bent Vismann

Sulfide tolerance: Physiological mechanisms and ecological implications

Abstract The discovery of macrofauna associated with sulfide-emitting deep-sea hydrothermal vents has stimulated research on physiological adaptations to sulfide in aerobic marine organisms. However, sulfide also occurs in marine sediments so that adaptations to sulfide are likely to be a very common phenomenon in the marine environment. The adaptations to sulfide in metazoans from the two types of habitats are discussed in terms of physiological mechanisms with special emphasis on animals without symbiotic sulfur bacteria. The physiological mechanisms are grouped into a hierarchy of sulfide defenses. The ecological implications of sulfide tolerance are discussed in terms of animal distribution and the fauna is suggested divided into sulfide tolerant and sulfide non-tolerant species.

Sulfide species and total sulfide toxicity in the shrimp Crangon crangon

The toxicity of total sulfide and individual sulfide species at different pH values were studied in Crangon crangon. The toxicity is evaluated both from external concentrations and internal sulfide concentrations and pH. Internal sulfide concentrations are calculated according to a diffusion model. C. crangon is very sensitive to sulfide having a LT50 of around 1 hour at 20 μM total sulfide (pH 8). During sulfide exposures it is exclusively H2S which diffuses into C. crangon, and sulfide toxicity is dependent on the concentration of H2S (i.e., pH dependent). No HS− toxicity was found. The correct quantification of sulfide concentration in exposure experiments are concluded to be H2S concentration. Exposed to increasing sulfide concentrations, C. crangon shows a distinct pattern of behavior which is correlated to hemolymph H2S concentration; at 0.1 μM hemolymph H2S C. crangon starts to swim, at 0.2 μM hemolymph H2S C. crangon starts to panic (i.e., abdominal constrictions) and at 0.4 μM hemolymph H2S C. crangon becomes paralysed.

Sulphide tolerance in Heteromastus filiformis (Polychaeta): Mitochondrial adaptations

Abstract Isolated mitochondria of Heteromastus filiformis detoxified sulphide. The mechanism worked best at low concentrations of up to 10 µmol l-1 sulphide. Sulphide inhibited mitochondrial cytochrome c oxidase in vitro at nanomolar concentrations (Ki: 0.37 ± 0.17 µmol l-1) , while catalase, another metal- containing enzyme, had a much higher inhibition constant (Ki: 790 ± 1u4 µmol l-l). Isolated mitochondria phosphorylated ADP using sulphide as substrate. The process had a maximum at 10 µmol l-1 sulphide (about 8 nmol ATP mg protein-1 min-1) H. filiforimis has a high anaerobic capacity and may accumulate up to 10.55 ± 1.06 µmol succinate g fresh mass-1 after 24 hours of hypoxia. We conclude that the worms switch to anaerobiosis to survive oxygen deficiency or periods in which the ambient sulphide levels are too high to permit detoxification by the mitochondria. These results are discussed in terms of hydrogen sulphide acting either as a toxic substance or as being useful in the species energy metabolism.

Anaerobic metabolism, hypoxia and hydrogen sulphide in the brackish water isopod Saduria entomon (L.)

Abstract The Baltic brackish water isopod Saduria entomon was simultaneously exposed to hydrogen sulphide (150 µmol 1−1 ) and hypoxia (4.0-6.7 kPa) for up to 100 hours. In contrast to haemoglobin-carrying species, the haemocyanin of S. entomon functions as oxyhaemocyanin also in the presence of hydrogen sulphide. The synthesis of new haemocyanin is, however, prevented. The hydrogen sulphide is oxidised in the midgut gland to S2O3 2− and SO3 2− Both lactate and alanine accumulate in the presence of hydrogen sulphide. When exposed to hypoxia and hydrogen sulphide anaerobic end products start to accumulate already at a water oxygen tension of at least 4.0–6.7 kPa, this means that hydrogen sulphide is correlated with an anaerobic metabolism.

Sulfide exposure experiments: The sulfide electrode and a set-up automatically controlling sulfide, oxygen and pH

A method for automatic control of hydrogen sulfide, oxygen and pH in exposure experiments is described. The set-up uses a computer to calculate and regulate experimental conditions. The regulation method is feedback control (i.e., closed loop process control). In test runs the computer based system has been shown to control experimental conditions. In a 24 h test run the set-up controlled the sulfide to 20.2 ± 1.1 μM, the oxygen to 0.51 ± 0.09 kPa and the pH to 7.50 ± 0.01. The electrochemistry of the Ag-Ag2S electrode for sulfide measurements is described and the practical use of the electrode empirical equations are given. The overall electrode performance is evaluated.

Recovery from hypoxia with and without sulfide in Saduria entomon: potassium, ATP and behavior

Abstract The contribution of potassium pumping, tissue ATP levels and locomotory activity to the oxygen debt was studied in the Baltic brackish water isopod Saduria entomon recovering from hypoxic and sulfidic conditions. The isopods were exposed (8 h; 9°C; salinity 10 ppt) to hypoxia (0.3 kPa) and to hypoxia (1 kPa) with sulfide (45 µM) and allowed to recover from hypoxia (8 h) and sulfide (28 h). When exposed to hypoxia the hemolymph and tissue K+ concentrations decreased significantly. When allowed 8 h recovery, normoxic K+ concentration was restored in the tissue but not in the hemolymph. After exposure to sulfide the hemolymph K+ was not different from the normoxic level but tissue K+ decreased significantly. When allowed 28 h of recovery the tissue K+ concentration was restored but the hemolymph K+ was significantly decreased as compared to the normoxic value. The ATP level in the normoxic control showed a significant decrease with time, indicating a general decrease in metabolic activity. The ATP level was significantly decreased after exposure to both hypoxia and sulfide. When allowed to recover, the ATP level in sulfide was significantly increased as compared to the normoxic value, indicating the occurrence of repair processes. During recovery from hypoxia and sulfide S. entomon showed no increase in locomotory activity. In terms of oxygen equivalents, re-establisment of potassium concentration contributed approximately 25 and 20% to the oxygen debt paid after exposure to hypoxia and sulfide, respectively. The results are discussed in relation to their contribution to the oxygen debt in S. entomon recovering from hypoxic and sulfidic exposure and possible processes not yet identified.

Oxygen binding characteristics of haemocyanin in the Baltic isopod Saduria entomon

Abstract The brackish water isopod Saduria entomon has a haemocyanin oxygen carrying capacity of 1.15 vol%. The physically dissolved oxygen corresponds to 0.66 vol% giving a total normoxic carrying capacity of 1.8 vol% (0.56 mmol-1-1). The haemocyanin shows a very high affinity for oxygen; at 6°C and pH of 8.1 and 7.7 P50 values were 1.7 and 8 Torr. Haemocyanin oxygen affinity was increased at 12°C compared to 6°C. In vivo pH values were 7.65 in normoxia and 7.93 in hypoxia 10–20% air saturation. Exposure to hypoxia (10–20% air saturation) for up to 18 days did not change the oxygen affinity of the haemocyanin. The metabolism of S. entomon remained aerobic during this hypoxic period, no metabolic endproduct like lactate or endproducts of nitrogen metabolism like urate accumulated. The influence of these affinity modulating factors on the blood pigment of S. entomon is thus negligible during environmental hypoxia. In vitro studies on pH in relation to PCO2 showed that pH was always higher in oxygenated com...

Modulators of haemocyanin oxygen affinity in the hypoxia- and sulphide-tolerant Baltic isopod Saduria entomon (L.).

Abstract. Dialysed haemocyanin from the isopod Saduria entomon had a considerably increased oxygen affinity (lower P50) and Bohr factor (–1.71) compared to native haemocyanin (Bohr factor –1.36) indicating that dialysis removes a small molecule size modulating factor decreasing the affinity of native haemolymph. Dialysed haemocyanin had a slightly lower co-operativity (2.42±0.3) than native haemocyanin (2.9±0.2). L-Lactate (10xa0mmolxa0l–1) improved oxygen affinity by 1–1.5xa0torr while urate had no effect. Mg2+ affected affinity in a pH-dependent manner (Bohr-factor increased to –1.67) while Ca2+ had no effect on the Bohr factor but increased affinity with ca 1xa0torr. Thiosulphate changed the Bohr factor to –1.75 to –1.82, similar to dialysed blood. Co-operativity was in neither case affected. The haemocyanin characteristics of S. entomon are similar to those of crustaceans from hydrothermal vents. These characteristics are probably general for crustaceans that are more or less permanently exposed to sulphide.

Effects of thiosulphate on haemocyanin oxygen affinity in the isopod Saduria entomon (L.) and the brown shrimp Crangon crangon (L.)

Abstract The sulphide-tolerant brackish water isopod Saduria entomon has haemocyanin with a high affinity for oxygen. Sulphide is oxidized in the hepatopancreas to thiosulphate. Oxygen needed for this oxidation is transported bound to haemocyanin. Thiosulphate was found to improve haemocyanin oxygen affinity in S.u2009entomon. The modulating effect was time and concentration dependent. The effect was greater at higher pH, i.e. the Bohr effect was greater (−1.82) compared to that seen without thiosulphate (−1.36). S.u2009entomon exposed to simultaneous severe hypoxia and sulphide had a low haemolymph pH and the partial pressure of oxygen required to reach 50% saturation was even lower than that measured inu2009vitro. This is ascribed to the combined effects of thiosulphate and lactate as well as unknown co-factors. Thiosulphate had no effect at all in the sulphide and hypoxia non-tolerant natantian Crangon crangon. It is suggested that thiosulphate can be important as a haemocyanin modulator for crustaceans digging in sulphide-rich sediments or constantly exposed to sulphide.