Sulphide tolerance in coastal halophytes

The effect of sulphide on the growth of several species of salt-marsh plants was investigated. Relative growth rates were significantly reduced in two upper-marsh species, Festuca rubra and Atriplex patula, and in the lower-marsh species Puccinellia maritima. However the growth of Salicornia europaea, a species frequently associated with sulphide-containing sediments, was unaffected. In a separate experiment the wide ranging halophyte Aster tripolium, also appeared to be tolerant of sulphide at a concentration frequently encountered in salt marshes. Sulphide pretreatment inhibited the activity of two metallo-enzymes, polyphenol oxidase and external phosphatase, in plants from the upper marsh, but had no effect on enzymes from P. maritima or S. europaea. The rate of respiration by root tissue was significantly reduced in all of the species investigated but whereas the uptake of ⁸⁶rubidium was markedly inhibited in the other three species, uptake by S. europaea showed a significant stimulation. Similarly, whereas sulphide-grown plants of F. rubra, A. patula and P. maritima had a considerably reduced tissue iron content, the total iron concentration in S. europaea tissues was comparable to that of the controls. When the sulphide-tolerant species A. tripolium was grown in sulphide-containing media there was no significant effect on the tissue concentration of any of the elements investigated. These results are discussed in relation to possible mechanisms of sulphide toxicity and resistance.     

Biotransformation of organic sulfides. Part 9. Formation of (S) para-substituted phenyl methyl sulfoxides by biotransformation usingHelminthosporium species NRRL 4671

Phenyl methyl sulfides substituted in thepara position with methyl, fluoro, chloro, bromo, cyano, nitro, amino, acyl, methoxy, thiomethyl and methylsulfinyl groups have been converted to (S) sulfoxides by biotransformation usingHelminthosporium species NRRL 4671. The highest yields and enantiomeric excesses were obtained with bromo, cyano, methoxy, thiomethyl and methylsulfinyl substituents and in two cases (para-Br and -CN) the products could be crystallized to give (S) sulfoxide of ≥ 96% ee.     

Post-treatment of fish canning effluents by sequential nitrification and autotrophic denitrification processes

In this research study a nitrifying/autotrophic denitrifying system was used for the post-treatment of an effluent coming from an anaerobic digester treating the wastewater produced in a fish canning industry. The nitrifying reactor achieved 100% of ammonia oxidation into nitrate. The effluent from this unit was fed to the autotrophic denitrifying reactor which treated a maximum sulphide loading rate (SLR) of 200 mg S^2?/L d with removal percentages of 100% and 30% for sulphide and nitrate, respectively. The low nitrate removal efficiency is attributed to sulphide limitations.The operational costs of this system were estimated as 0.92 €/kg N_removed, lower than those for conventional nitrification/denitrification processes. For nitrogen removal the SHARON/anammox processes is the cheapest option. However the combination of nitrification and autotrophic denitrification (using elemental sulphur) processes would present a better operational stability compared to the SHARON/anammox system.     

Responses of intertidal nematodes to short-term anoxic events

We investigated tolerance to, and activity of, nematodes in hypoxic and anoxic/partially sulphidic conditions and their ability for recovery after reoxygenation of anoxic sediment. To this end, sediments from an intertidal flat were incubated under oxic, suboxic and anoxic/partially sulphidic conditions for a 14-day period and the final density of nematodes, as a group, and of the most abundant species were assessed. In one treatment, oxygen was restored after anoxic incubation. The incorporation of ¹³C, originating from labeled algae added on top of the sediment, was taken as an indication of nematode activity.Short-term suboxic and anoxic/partially sulphidic conditions had similar structuring impact on the nematode community, reducing total densities by about one third. Survival in suboxic and anoxic/partially sulphidic conditions was species-specific. Daptonema setosum, D. tenuispiculum and Chromadora macrolaima, dominant in the oxic incubation, disappeared when the oxygen level was reduced. The density of the other dominant species was slightly reduced (Sabatieria pulchra), similar (Terschellingia communis) or even increased in the suboxic and anoxic conditions (Metachromadora vivipara). The activity level of these three species was, however, reduced under oxygen limitation. Our results are discussed in terms of the life-history strategies of these species.     

Physiological responses of the seagrass Posidonia oceanica to elevated organic matter content in sediments: An experimental assessment

Here we studied the effects of adding organic carbon and nutrients to sediment on the physiology and survival of the seagrass Posidonia oceanica in a field experiment in the Medes Islands (NE Spain). Nine randomly selected plots were established at a depth of 10 m; three were enriched with organic carbon (OM treatment), three with organic carbon and nutrients (OMN treatment), and three were kept as controls (CON). The experiment was performed over 5 months and sampling of plants and sediments was done in March, May and July 2002. Sediment sulfide pools and pore water ammonium concentrations increased significantly in OM and OMN plots, both treatments showing increased reducing conditions in the sediment. Plants in these two treatments showed higher mortality and lower biomass compared to plants from CON plots. The greatest effects on seagrass occurred in the OMN plots, indicating a synergistic effect of organic carbon and nutrient additions. Treatments had significant effects on plant nitrogen (N) and phosphorous (P) metabolism, shown by an increase in free amino acid (FAA) content, a change in FAA composition and a lack of increase in N and P tissue content. Treated plants showed higher g-aminobutyric acid (GABA) and malate concentrations and lower concentrations of non-structural carbohydrates compared to CON, indicating that anaerobic respiration in below-ground tissues occurred. Several of the physiological changes shown by P. oceanica can be interpreted as adaptations to anoxia exposure. However, the increased mortality in treated plots demonstrates that this seagrass does not tolerate highly reduced sediments.     

Sulphide detoxification in Hediste diversicolor and Marenzelleria viridis, two dominant polychaete worms within the shallow coastal waters of the southern Baltic Sea

The polychaete worms Marenzelleria viridis (Verrill 1873) and Hediste diversicolor (O.F. Müller) form the main part of the macro-zoobenthos in soft-bottomed shallow inlets of the Baltic Sea. Due to high eutrophication within these waters the animals are exposed to low oxygen and high sulphide concentrations. Specimens of both species from a low salinity location (S 8 ‰) were compared concerning their physiological abilities in coping with this hostile environment. Sulphide detoxification occurred in both polychaetes even during severe hypoxia with the main end-product being thiosulphate. In absence of sulphide nearly no end-products of anaerobic metabolism were found in the worms during moderate hypoxia (pO₂=7 kPa). In presence of hydrogen sulphide, succinate, a sensitive indicator of anaerobic metabolism, was accumulated in higher amounts at low sulphide concentrations (0.3 mM) already. Oxygen consumption and ATP production was determined in isolated mitochondria of both species. Both polychaetes were able to perform enzymatic sulphide oxidation in the mitochondria at concentrations up to 50 μM. This process was coupled with oxidative phosphorylation. At least in M. viridis sulphide respiration was not completely inhibited by cyanide, suggesting an alternative oxidation pathway, which by-passes the cytochrome-c-oxidase. The two species did not differ in the rate of sulphide detoxification, but H. diversicolor produced about as twice as much ATP from mitochondrial sulphide oxidation. Differences in mitochondrial sulphide oxidation are probably related to the different life strategies of the worms.     

Hypoxia and sulphide influence gamete production in Ulva sp.

Gamete production after exposure to hypoxia or sulphide was studied in the marine macroalga Ulva sp. collected in the Sacca di Goro, Italy. Experiments were carried out on discs (12 mm diameter) of thalli cultured in artificial sea water in laboratory at 20 ± 1 °C, 152 μmol m⁻² s⁻¹, 16 h photoperiod and 30‰ salinity. Dehydration of thallus was used as inducer of gametogenesis and growth and gamete release during recovery after 10, 20, 30 or 40 min dehydration (20 ± 1 °C, 25% humidity) were analysed. Unlike non-dehydrated thalli the dehydrated ones produced gametes. Thallus discs, non-dehydrated or subjected to 30 min dehydration, were exposed to hypoxia (1.78–4.02 μmol O₂ L⁻¹) or sulphide (1 mM) for 3, 5, or 7 days at 20 °C in the dark. Non-dehydrated and dehydrated thalli maintained in normoxic conditions in the dark were the controls. Gamete density was checked by counting at the end of the incubation period and during the subsequent 7 days of recovery under 16 h photoperiod in normoxic conditions. Non-dehydrated thalli maintained in normoxic conditions in the dark released gametes when returned to light suggesting that dark constitutes a stimulus to gamete production. The presence of gametes at the end of 3 days incubation of dehydrated thalli in normoxia demonstrated that gametogenesis can occur even in the dark. However, gametes were not present at the end of incubation in hypoxic and sulphidic conditions. Actually, during hypoxic incubation oxygen consumption in D-thalli was very low, only 0.117 × 10⁻³ μmol O₂ mg⁻¹ h⁻¹ compared to 5.93 × 10⁻³ μmol O₂ mg⁻¹ h⁻¹ in normoxia, denoting a reduction of the metabolic rate that could not sustain gametogenesis. During recovery after incubation in normoxic, hypoxic or sulphidic conditions densities of gametes from dehydrated thalli showed significant differences and resulted after hypoxia > after normoxia > after sulphide. Differences in non-dehydrated thalli were not significant. Dehydrated thalli, still green at the end of the incubation period, underwent blanching in the course of recovery in parallel to gamete production, while non-dehydrated thalli maintained their green colour even after exposure to sulphide. Our findings suggest that macroalga Ulva sp. can survive exposure to darkness, severe hypoxia and high sulphide levels and can maintain gamete production even when the exposure to these stress conditions is joined to dehydration.     

Oxidation of hydrogen sulphide in sour gas by Chlorobium limicola

The aim of this work was to assess the potential for bacterial oxidation of hydrogen sulphide as a purification method of sour gas. Using a continuous culture of Chlorobium limicola, high efficiencies of oxidation of both soluble and gaseous sulphide were achieved, with efficiencies for the latter exceeding 95%. Sulphide added as aqueous sodium sulphide was converted to sulphur and sulphate with almost total removal of the initial 100 mg S l⁻¹ within 24 h. Gaseous sulphide was oxidized at an efficiency of 95% (approximately 3 mmol S h⁻¹ (unit biomass Abs)⁻¹) over 1 h runs at a gas flow rate of 60 ml min⁻¹. With a sulphur recovery system to prevent sulphur accumulation, an efficiency of 70% was maintained. Biological removal of sulphide represents a potentially important biotechnological process, with high potential for viable scale up.     

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

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. entomon. 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. entomon 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 in vitro. 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. Accepted: 11 August 1999     

Sulphide release from anoxic sediments in relation to iron availability and organic matter recalcitrance and its effects on inorganic phosphorus recycling

This research aims to analyse the sediment capacity to buffer free sulphide release in three coastal lagoons which differ in terms of eutrophication level, tide influence and primary producer communities. A preliminary estimate of soluble reactive phosphorus (SRP) regeneration coupled with sulphide fluxes is also made. Sediment profiles of ferrous and ferric iron and reduced sulphur pools were determined in three stations in the Bassin d'Arcachon (South West France), in one site in the Etang du Prévost lagoon (Southern France), and in three stations in the Sacca di Goro lagoon (Northern Italy). Laboratory experiments were also conducted by incubating sediment slurries. Slurries from the French lagoons were also enriched with about 2% d.w. of organic detritus obtained from the dominant macrophytes of each site, namely Zostera noltii and Ruppia cirrhosa (Bassin d'Arcachon), and Ulva rigida (Etang du Prévost). In the Sacca di Goro, slurry experiments were conducted at two sites with different salinity range, sediment composition and hydrodynamics.Field data showed that concentrations of available iron (Fe(II)+Fe(III)) ranged from a minimum of 28.5 µmol cm^–3 (Etang du Prévost) to a maximum of 275.7 µmol cm^–3 (Sacca di Goro). Moreover, in the French lagoons, acid volatile sulphide (AVS) accumulation in the superficial sediment was related to ferrous iron concentrations. Laboratory experiments showed that in spite of strong reducing conditions, sulphide and SRP release was weaker in iron-rich sediments and in those enriched with the most refractory organic matter. The highest fluxes were detected in sediment slurries from the Etang du Prévost, which had the lowest iron content, supplied by 2% of the labile detritus from Ulva rigida. In this case, SRP release was directly related to sulphide production.Two factors seem significant to evaluate the buffer capacity against free sulphide and SRP release from anoxic sediment: organic matter biodegradability, which forces sediment toward reducing conditions, and iron availability, which can affect sulphide mobility as well as the iron hydroxide-phosphate-sulphide system.