Uptake Of Sulfide Research Articles

Wastewater-Enhanced Microbial Corrosion of Concrete Sewers.

Microbial corrosion of concrete in sewers is known to be caused by hydrogen sulfide, although the role of wastewater in regulating the corrosion processes is poorly understood. Flooding and splashing of wastewater in sewers periodically inoculates the concrete surface in sewer pipes. No study has systematically investigated the impacts of wastewater inoculation on the corrosion of concrete in sewers. This study investigated the development of the microbial community, sulfide uptake activity, and the change of the concrete properties for coupons subjected to periodic wastewater inoculation. The concrete coupons were exposed to different levels of hydrogen sulfide under well-controlled conditions in laboratory-scale corrosion chambers simulating real sewers. It was evident that the periodic inoculation induced higher corrosion losses of the concrete in comparison to noninoculated coupons. Instantaneous measurements such as surface pH did not reflect the cumulative corrosion losses caused by long-term microbial activity. Analysis of the long-term profiles of the sulfide uptake rate using a Gompertz model supported the enhanced corrosion activity and greater corrosion loss. The enhanced corrosion rate was due to the higher sulfide uptake rates induced by wastewater inoculation, although the increasing trend of sulfide uptake rates was slower with wastewater. Increased diversity in the corrosion-layer microbial communities was detected when the corrosion rates were higher. This coincided with the environmental conditions of increased levels of gaseous H2S and the concrete type.

Light-dependent sulfide oxidation in the anoxic zone of the Chesapeake Bay can be explained by small populations of phototrophic bacteria.

Microbial sulfide oxidation in aquatic environments is an important ecosystem process, as sulfide is potently toxic to aerobic organisms. Sulfide oxidation in anoxic waters can prevent the efflux of sulfide to aerobic water masses, thus mitigating toxicity. The contribution of phototrophic sulfide-oxidizing bacteria to anaerobic sulfide oxidation in the Chesapeake Bay and the redox chemistry of the stratified water column were investigated in the summers of 2011 to 2014. In 2011 and 2013, phototrophic sulfide-oxidizing bacteria closely related to Prosthecochloris species of the phylum Chlorobi were cultivated from waters sampled at and below the oxic-anoxic interface, where measured light penetration was sufficient to support populations of low-light-adapted photosynthetic bacteria. In 2012, 2013, and 2014, light-dependent sulfide loss was observed in freshly collected water column samples. In these samples, extremely low light levels caused 2- to 10-fold increases in the sulfide uptake rate over the sulfide uptake rate under dark conditions. An enrichment, CB11, dominated by Prosthecochloris species, oxidized sulfide with a Ks value of 11 μM and a Vmax value of 51 μM min(-1) (mg protein(-1)). Using these kinetic values with in situ sulfide concentrations and light fluxes, we calculated that a small population of Chlorobi similar to those in enrichment CB11 can account for the observed anaerobic light-dependent sulfide consumption activity in natural water samples. We conclude that Chlorobi play a far larger role in the Chesapeake Bay than currently appreciated. This result has potential implications for coastal anoxic waters and expanding oxygen-minimum zones as they begin to impinge on the photic zone.

Impact of fluctuations in gaseous H2S concentrations on sulfide uptake by sewer concrete: The effect of high H2S loads

The acid production from the oxidation of hydrogen sulfide (H2S) in sewer air results in serious corrosion of exposed concrete surfaces in sewers. Large fluctuations of gaseous H2S concentrations occur in sewers due to the diurnal profiles of sewage flow and retention times and the necessity of intermittent pumping of sewage from pressure pipes into gravity pipes. How the high concentrations of H2S due to these events may affect H2S uptake and subsequent corrosion by concrete sewers is largely unknown. This study determined the effect of short- and long-term increases in H2S levels on the sulfide uptake rate (SUR) of concrete surfaces with an active corrosion layer. The results showed that during the high load situation the SUR increased significantly but then decreased (compared to the baseline SUR) by about 7–14% and 41–50% immediately after short- and long-term H2S high-load periods, respectively. For both exposure conditions, the SUR gradually (over several hours) recovered to approximately 90% of the baseline SUR. Further tests suggest multiple factors may contribute to the observed decrease of SUR directly after the high H2S load. This includes the temporary storage of elemental sulfur in the corrosion layer and inhibition of sulfide oxidizing bacteria (SOB) due to high H2S level and temporary acid surge. Additionally, the delay of the corrosion layer to fully recover the SUR after the high H2S load suggests that there is a longer-term inhibitive effect of the high H2S levels on the activity of the SOB in the corrosion layer. Due to the observed activity reductions, concrete exposed to occasional short-term high H2S load periods had an overall lower H2S uptake compared to concrete exposed to constant H2S levels at the same average concentration. To accurately predict H2S uptake by sewer concrete and hence the likely maximum corrosion rates, a correction factor should be adopted for the H2S fluctuations when average H2S levels are used in the prediction.

Multifunctional Purification and Sensing of Toxic Hydride Gases by CuBTC Metal–Organic Framework

In this report, we evaluate the metal–organic framework CuBTC as a real-world adsorbent for protection against three toxic hydride gases: ammonia, arsine, and hydrogen sulfide. We develop a scalable room-temperature synthesis of high-surface-area CuBTC using a benign ethanol–water solvent system. We test the capacity of CuBTC for the hydride gases under microbreakthrough and real-world packed-bed conditions at both low and high humidity conditions. Under microbreakthrough conditions, CuBTC outperforms a broad-spectrum carbon (BSC) adsorbent for uptake of ammonia and arsine, with approximately equivalent uptake of hydrogen sulfide. Under packed-bed conditions, CuBTC outperforms the BSC for ammonia uptake but offers little protection against arsine or hydrogen sulfide. We demonstrate the potential for CuBTC to act not only as an effective adsorbent for ammonia but also for sensing and to indicate saturation on the basis of colorimetric and fluorescence changes. We find that CuBTC is a suitable material for ...

Evolutionary radiation of shallow-water Lucinidae (Bivalvia with endosymbionts) as a result of the rise of seagrasses and mangroves

The Lucinidae (Bivalvia) originated in the Silurian Period with adaptations and life habits like those of modern members of this family. Nonetheless, the family remained at very low diversity until beginning a remarkable evolutionary radiation near the end of the Cretaceous Period, when seagrasses and mangroves arose. These marine angiosperms provided protective habitats in which the lucinids suddenly began to flourish, taking advantage of the dysaerobic sediments below roots and rhizomes to acquire sulfides for the endosymbiotic bacteria that they harbor in their gills and employ as food. Lucinids entered a symbiotic relationship with seagrasses, which benefit from the endosymbionts’ uptake of toxic sulfide, and it is in seagrass meadows that they have by far their highest diversity in shallow seas today. The terminal Cretaceous mass extinction had little impact on the taxonomic diversity of lucinids. Presumably they relied heavily on endosymbionts for nutrition at a time when marine pelagic productivity collapsed and many suspension-feeding taxa died out. The lucinids continued their radiation into the Cenozoic Era without interruption.

A microbiological and biogeochemical investigation of the cold seep tubeworm Escarpia southwardae (Annelida: Siboglinidae): Symbiosis and trace element composition of the tube

Tubeworms within the annelid family Siboglinidae rely on sulfur-oxidizing autotrophic bacterial symbionts for their nutrition, and are among the dominant metazoans occurring at deep-sea hydrocarbon seeps. Contrary to their relatives from hydrothermal vents, sulfide uptake for symbionts occurs within the anoxic subsurface sediment, in the posterior ‘root’ region of the animal. This study reports on an integrated microbiological and geochemical investigation of the cold seep tubeworm Escarpia southwardae collected at the Regab pockmark (Gulf of Guinea). Our aim was to further constrain the links between the animal and its symbiotic bacteria, and their environment. We show that E. southwardae harbors abundant sulfur-oxidizing bacterial symbionts in its trophosome. Symbionts are able to fix inorganic carbon using the Calvin-Benson cycle, as reported in most other Siboglinidae, but can also use the reverse Tricarboxilic Acid Cycle. Surprisingly, the observed bacteria appear to be more closely related to symbionts of Escarpia and Lamellibrachia species from very distant sites located in the Gulf of Mexico and eastern Pacific, than to symbionts of a siboglinid occurring at a nearby methane seep site, only a few hundred km away from Regab. Then, by combining scanning electron microscopy and trace element (Mn, Fe, Sr, Zr) analyses of E. southwardae tube, we also show that two distinct oxidation fronts occur along the tube. The first one, near the posterior end of the tube, corresponds to the interface between oxic bottom waters and the underlying anoxic sediment. In contrast, the second redox front is located in the most anterior part of the tube, and could result from active oxygen uptake by the plume of the tubeworm. We speculate that intense oxygen consumption in this region could create favorable conditions for sulfate reduction by specialized bacteria associated with the plume, possibly leading to an additional source of dissolved sulfide that would further enhance the productivity of bacterial symbionts.

A rapid, non-destructive methodology to monitor activity of sulfide-induced corrosion of concrete based on H2S uptake rate

Many existing methods to monitor the corrosion of concrete in sewers are either very slow or destructive measurements. To overcome these limitations, a rapid, non-invasive methodology was developed to monitor the sulfide-induced corrosion process on concrete through the measurement of the H2S uptake rates of concrete at various corrosion stages. The H2S uptake rate for a concrete coupon was determined by measuring the gaseous H2S concentrations over time in a temperature- and humidity-controlled gas-tight reactor. The reliability of this method was evaluated by carrying out repeated tests on different concrete coupons previously exposed to 50 ppm of H2S, at 30 °C and 100% relative humidity for over 32 months. The H2S uptake measurements showed good reproducibility. It was also shown that a severely corroded coupon exhibited higher sulfide uptake rates than a less corroded coupon. This could be explained by the corrosion layer in the more corroded coupon having a higher biological sulfide oxidation activity than the less corroded coupon. Additionally, temperature changes had a stronger effect on the uptake rate of the heavily corroded coupon compared to the less corroded coupon. A corrosion rate of 8.9 ± 0.5 mm/year, estimated from the H2S uptake results, agreed well with the corrosion rate observed in real sewers under similar conditions. The method could be applied to investigate important factors affecting sulfide-induced concrete corrosion, particularly temperature, fluctuating gaseous H2S concentrations, oxygen concentrations, surface pH and relative humidity.

Design of Ratiometric Fluorescent Probes Based on Arene–Metal‐Ion Interactions and Their Application to CdII and Hydrogen Sulfide Imaging in Living Cells

Non-coordinative interactions between a metal ion and the aromatic ring of a fluorophore can act as a versatile sensing mechanism for the detection of metal ions with a large emission change of fluorophores. We report the design of fluorescent probes based on arene-metal-ion interactions and their biological applications. This study found that various probes having different fluorophores and metal binding units displayed significant emission redshift upon complexation with metal ions, such as Ag(I), Cd(II), Hg(II), and Pb(II). X-ray crystallography of the complexes confirmed that the metal ions were held in close proximity to the fluorophore to form an arene-metal-ion interaction. Electronic structure calculations based on TDDFT offered a theoretical basis for the sensing mechanism, thus showing that metal ions electrostatically modulate the energy levels of the molecular orbitals of the fluorophore. A fluorescent probe was successfully applied to the ratiometric detection of the uptake of Cd(II) ions and hydrogen sulfide (H2S) in living cells. These results highlight the utility of interactions between arene groups and metal ions in biological analyses.

Selectivity of layered double hydroxides and their derivative mixed metal oxides as sorbents of hydrogen sulfide

In the context of finding high efficient sorbent materials for removing hydrogen sulfide (H2S) from air stream, a screening study was performed to find the best combination of metals for the synthesis of layered double hydroxides (LDHs) and their derivative mixed metal oxides. Based on selectivity of 998 natural mineral species of sulfur-containing compounds, Cu2+, Ni2+ and Zn2+ were selected as divalent metals, and Fe3+, Al3+ and Cr3+ as trivalent metals to synthesis the LDHs sorbents. 10 LDHs materials and their calcined mixed metal oxides, Ni0.66Al0.34, Cu0.35Ni0.32Al0.33, Zn0.66Al0.34, Cu0.36Zn0.32Al0.32, Ni0.64Fe0.36, Cu0.35Ni0.31Fe0.34, Ni0.66Cr0.34, Cu0.35Ni0.31Cr0.34, Zn0.66Cr0.34, Cu0.33Zn0.32Cr0.35 were synthesized, characterized chemically and physically, and then tested using breakthrough test to determine their sulfur uptake. Ni0.64Fe0.36 mixed metal oxides was found to have the best uptake of hydrogen sulfide (136mg H2S/g). Regeneration of spent Ni0.64Fe0.36 mixed metal oxides was studied using two different mixture solutions, NaCl/NaOH and acetate-buffer/NaCl/NaOH. The latter mixture successfully desorbed the sulfur from the Ni0.64Fe0.36 sorbent for 2 cycles of regeneration/sorption.

Computational screening of porous carbons, zeolites, and metal organic frameworks for desulfurization and decarburization of biogas, natural gas, and flue gas

Eighteen kinds of porous materials from carbons, zeolites, and metal organic frameworks (MOFs) have been extensively investigated for desulfurization and decarburization of the biogas, natural gas, and flue gas by using a molecular modeling approach. By considering not only the selectivity but also capacity, Na‐5A, zeolite‐like MOF (zMOF), and Na‐13X, MIL‐47 are screened as the most promising candidates for removal of sulfide in the CH4CO2H2S and N2CO2SO2 systems, respectively. However, for simultaneous removal of sulfide and CO2, the best candidates are zMOF for the natural gas and biogas (i.e., CH4CO2H2S system) and MOF‐74‐Zn for the flue gas (i.e., N2CO2SO2 system). Moreover, the regeneration ability of the recommended adsorbents is further assessed by studying the effect of temperature on adsorption. It is found that compared to the zMOF and MIL‐47 MOFs, the Na‐5A and Na‐13X zeolites are not easily regenerated due to the difficulty in desorption of sulfide at high temperature, which results from the stronger adsorbent–adsorbate interactions in zeolites. The effect of sulfide concentration on the adsorption properties of the recommended adsorbents is also explored. We observe that the zMOF and MIL‐47 are also superior to the Na‐5A and Na‐13X for desulfurization of gas mixtures containing high sulfide concentration. This is because MOFs with larger pore volume lead to a greater sulfide uptake. The effects of porosity, framework density, pore volume, and accessible surface area on the separation performance are analyzed. The optimum porosity is about 0.5–0.6, to meet the requirements of both high selectivity and uptake. It is expected this work provides a useful guidance for the practical applications of desulfurization and decarburization. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2928–2942, 2013

Observations of the uptake of carbonyl sulfide (COS) by trees under elevated atmospheric carbon dioxide concentrations

Abstract. Global change forces ecosystems to adapt to elevated atmospheric concentrations of carbon dioxide (CO2). We understand that carbonyl sulfide (COS), a trace gas which is involved in building up the stratospheric sulfate aerosol layer, is taken up by vegetation with the same triad of the enzymes which are metabolizing CO2, i.e. ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEP-Co) and carbonic anhydrase (CA). Therefore, we discuss a physiological/biochemical acclimation of these enzymes affecting the sink strength of vegetation for COS. We investigated the acclimation of two European tree species, Fagus sylvatica and Quercus ilex, grown inside chambers under elevated CO2, and determined the exchange characteristics and the content of CA after a 1–2 yr period of acclimation from 350 ppm to 800 ppm CO2. We demonstrate that a compensation point, by definition, does not exist. Instead, we propose to discuss a point of uptake affinity (PUA). The results indicate that such a PUA, the CA activity and the deposition velocities may change and may cause a decrease of the COS uptake by plant ecosystems, at least as long as the enzyme acclimation to CO2 is not surpassed by an increase of atmospheric COS. As a consequence, the atmospheric COS level may rise causing an increase of the radiative forcing in the troposphere. However, this increase is counterbalanced by the stronger input of this trace gas into the stratosphere causing a stronger energy reflection by the stratospheric sulfur aerosol into space (Brühl et al., 2012). These data are very preliminary but may trigger a discussion on COS uptake acclimation to foster measurements with modern analytical instruments.

Trophic cascade induced by molluscivore predator alters pore‐water biogeochemistry via competitive release of prey

Effects of predation may cascade down the food web. By alleviating interspecific competition among prey, predators may promote biodiversity, but the precise mechanisms of how predators alter competition have remained elusive. Here we report on a predator-exclosure experiment carried out in a tropical intertidal ecosystem, providing evidence for a three-level trophic cascade induced by predation by molluscivore Red Knots (Calidris canutus) that affects pore water biogeochemistry. In the exclosures the knots' favorite prey (Dosinia isocardia) became dominant and reduced the individual growth rate in an alternative prey (Loripes lucinalis). Dosinia, a suspension feeder, consumes suspended particulate organic matter (POM), whereas Loripes is a facultative mixotroph, partly living on metabolites produced by sulfur-oxidizing chemoautotrophic bacteria, but also consuming suspended POM. Reduced sulfide concentrations in the exclosures suggest that, without predation on Dosinia, stronger competition for suspended POM forces Loripes to rely on energy produced by endosymbiotic bacteria, thus leading to an enhanced uptake of sulfide from the surrounding pore water. As sulfide is toxic to most organisms, this competition-induced diet shift by Loripes may detoxify the environment, which in turn may facilitate other species. The inference that predators affect the toxicity of their environment via a multi-level trophic cascade is novel, but we believe it may be a general phenomenon in detritus-based ecosystems.

Association between Carbonyl Sulfide Uptake and 18Δ during Gas Exchange in C3 and C4 Leaves

Carbonyl sulfide (COS) and C(18)OO exchange by leaves provide potentially powerful tracers of biosphere-atmosphere CO(2) exchange, and both are assumed to depend on carbonic anhydrase (CA) activity and conductance along the diffusive pathway in leaves. We investigated these links using C(3) and C(4) plants, hypothesizing that the rates of COS and C(18)OO exchange by leaves respond in parallel to environmental and biological drivers. Using CA-deficient antisense lines of C(4) and C(3) plants, COS uptake was essentially eliminated and discrimination against C(18)OO exchange ((18)Δ) greatly reduced, demonstrating CA's key role in both processes. (18)Δ showed a positive linear correlation with leaf relative uptake (LRU; ratio of COS to CO(2) assimilation rates, A(s)/A(c), normalized to their respective ambient concentrations), which reflected the effects of stomatal conductance on both COS and C(18)OO exchange. Unexpectedly, a decoupling between A(s) and (18)Δ was observed in comparing C(4) and C(3) plants, with a large decrease in (18)Δ but no parallel reduction in A(s) in the former. This could be explained by C(4) plants having higher COS concentrations at the CA site (maintaining high A(s) with reduced CA) and a high phosphoenolpyruvate carboxylase/CA activity ratio (reducing (18)O exchange efficiency between CO(2) and water, but not A(s)). Similar A(s) but higher A(c) in C(4) versus C(3) plants resulted in lower LRU values in the former (1.16 ± 0.20 and 1.82 ± 0.18 for C(4) and C(3), respectively). LRU was, however, relatively constant in both plant types across a wide range of conditions, except low light (<191 μmol photon m(-2) s(-1)).

Heterogeneous uptake of carbonyl sulfide onto kaolinite within a temperature range of 220–330 K

In this study the heterogeneous uptake of carbonyl sulfide (OCS) onto kaolinite was investigated using a Knudsen cell reactor within the temperature range of 220–330 K. Results showed that OCS could only be adsorbed at Al‐OH sites on kaolinite reversibly within this temperature region. The initial true uptake coefficient was measured to be (1.68 ± 0.12) × 10−7 at 300 K. It showed no observable dependence on the pressure of OCS, while it varied significantly with temperature, and can be expressed as γt = exp(1293/T − 20.0)/[1 + exp(1293/T − 20.0]. The values of ΔHobs and ΔSobs during the adsorption process were −10.7 ± 1.1 kJ mol−1 and −166.3 ± 4.5 J K−1 mol−1, respectively. The activation energy for desorption of OCS on kaolinite was 19.5 ± 1.1 kJ mol−1. The uptake of OCS by kaolinite owing to reversible physisorption may have little influence on the sink of OCS in the atmosphere.

Chemical and morphological characterization of mesoporous material supported copper oxide nanoparticles for potential application

SBA-15 supported nano-scaled copper oxide was synthesized by impregnation method via ultrasonic-assisted route. The removal test from gas mixture containing 0.1 vol.% hydrogen sulfide was carried out over this material at atmospheric conditions. The effects of the chemical nature of copper oxide and the textural properties of the material on removal capacity were studied. The materials before and after the removal test were analyzed by nitrogen adsorption, X-ray diffraction, Transmission Electron Microscope, X-ray photoelectron Spectroscopy, Fourier Transform Infrared Spectrometer and Inductive Coupled Plasma. The results showed that copper species are located predominantly in mesopore channels, existing as copper oxide nanoparticles. Mesopores are active sites for removal reaction. The outstanding performance of hydrogen sulfide uptake capacity is attributed to a combination of the nature of the active centers and the well-proportioned distribution of active phase inside the mesoporous material.

Phosphate geochemistry, mineralization processes, and Thioploca distribution in shelf sediments off central Chile

Sediments underlying the major costal upwelling systems of the world oceans are hot-spots of modern formation of hydroxyapatites, often associated with benthic communities of large, nitrate-accumulating sulfur bacteria. We studied the association between phosphate release, organic phosphorus mineralization, and occurrence of dense communities of the filamentous sulfur bacteria, Thioploca spp., on the continental shelf off central Chile during the austral summer when high phytoplankton productivity and anoxic bottom water prevailed. Freshly deposited phytodetritus stimulated extremely high sulfate reduction rates, which supported a large Thioploca community of up to 100 g biomass per m 2. Effective bacterial sulfide uptake kept the sulfide concentration low, which enabled the accumulation of free iron, thus demonstrating intensive iron reduction concurrent with sulfate reduction. Phosphate released to the pore water reached 100–300 μM peak concentrations within the uppermost 0–5 cm and phosphate was lost to the overlying anoxic water column. The large phosphate release was not directly related to the presence of Thioploca but was rather the result of a high deposition and mineralization rate of fresh organic detritus. Although the pore water was super–saturated with respect to hydroxyapatite, this mineral was only a minor P-component in the sediment. Most solid-phase phosphate was bound to iron.

Layer‐by‐Layer Nano‐Encapsulation of Microbes: Controlled Cell Surface Modification and Investigation of Substrate Uptake in Bacteria

LbL nano self-assembly coating of A. vinosum with different polyelectrolyte combinations is presented as an example to investigate substrate uptake in bacteria. The effects of surface charge and the formation of a physical barrier provides new insights in the contact mechanisms between the cell surface and insoluble elemental sulfur. Furthermore, uptake of sulfide by encapsulated cells was investigated. Growth experiments of coated cells showed that surface charge did neither affect sulfide uptake nor the contact formation between the cells and solid sulfur. However, increasing layers slowed or inhibited the uptake of sulfide and elemental sulfur. This work demonstrates how defining surface properties of bacteria has potential for microbiological and biotechnological applications.

Modeling of Hydrogen Sulfide Oxidation in Concrete Corrosion Products from Sewer Pipes

Abiotic and biotic oxidation of hydrogen sulfide related to concrete corrosion was studied in corrosion products originating from a sewer manhole. The concrete corrosion products were suspended in an acidic solution, mimicking the conditions in the pore water of corroded concrete. The removal of hydrogen sulfide and dissolved oxygen was measured in parallel in the suspension, upon which the suspension was sterilized and the measurement repeated. The results revealed the biotic oxidation to be fast compared with the abiotic oxidation. The stoichiometry of the hydrogen sulfide oxidation was evaluated using the ratio between oxygen and hydrogen sulfide uptake. The ratio for the biotic oxidation pointed in the direction of elemental sulfur being formed as an intermediate in the oxidation of hydrogen sulfide to sulfuric acid. The experimental results were applied to suggest a hypothesis and a mathematical model describing the hydrogen sulfide oxidation pathway in a matrix of corroded concrete.

Physiology and behaviour of marine Thioploca

Among prokaryotes, the large vacuolated marine sulphur bacteria are unique in their ability to store, transport and metabolize significant quantities of sulphur, nitrogen, phosphorus and carbon compounds. In this study, unresolved questions of metabolism, storage management and behaviour were addressed in laboratory experiments with Thioploca species collected on the continental shelf off Chile. The Thioploca cells had an aerobic metabolism with a potential oxygen uptake rate of 1760 micromol O2 per dm(3) biovolume per h, equivalent to 4.4 nmol O2 per min per mg protein. When high ambient sulphide concentrations (approximately 200 microM) were present, a sulphide uptake of 6220+/-2230 micromol H2S per dm(3) per h, (mean+/-s.e.m., n=4) was measured. This sulphide uptake rate was six times higher than the oxidation rate of elemental sulphur by oxygen or nitrate, thus indicating a rapid sulphur accumulation by Thioploca. Thioploca reduce nitrate to ammonium and we found that dinitrogen was not produced, neither through denitrification nor through anammox activity. Unexpectedly, polyphosphate storage was not detectable by microautoradiography in physiological assays or by staining and microscopy. Carbon dioxide fixation increased when nitrate and nitrite were externally available and when organic carbon was added to incubations. Sulphide addition did not increase carbon dioxide fixation, indicating that Thioploca use excess of sulphide to rapidly accumulate sulphur rather than to accelerate growth. This is interpreted as an adaptation to infrequent high sulphate reduction rates in the seabed. The physiology and behaviour of Thioploca are summarized and the adaptations to an environment, dominated by infrequent oxygen availability and periods of high sulphide abundance, are discussed.

Sulfide assimilation by ectosymbionts of the sessile ciliate, Zoothamnium niveum.

We investigated the constraints on sulfide uptake by bacterial ectosymbionts on the marine peritrich ciliate Zoothamnium niveum by a combination of experimental and numerical methods. Protists with symbionts were collected on large blocks of mangrove-peat. The blocks were placed in a flow cell with flow adjusted to in situ velocity. The water motion around the colonies was then characterized by particle tracking velocimetry. This shows that the feather-shaped colony of Z. niveum generates a unidirectional flow of seawater through the colony with no recirculation. The source of the feeding current was the free-flowing water although the size of the colonies suggests that they live partly submerged in the diffusive boundary layer. We showed that the filtered volume allows Z. niveum to assimilate sufficient sulfide to sustain the symbiosis at a few micromoles per liter in ambient concentration. Numerical modeling shows that sulfide oxidizing bacteria on the surfaces of Z. niveum can sustain 100-times higher sulfide uptake than bacteria on flat surfaces, such as microbial mats. The study demonstrates that the filter feeding zooids of Z. niveum are preadapted to be prime habitats for sulfide oxidizing bacteria due to Z. niveum’s habitat preference and due to the feeding current. Z. niveum is capable of exploiting low concentrations of sulfide in near norm-oxic seawater. This links its otherwise dissimilar habitats and makes it functionally similar to invertebrates with thiotrophic symbionts in filtering organs.Electronic supplementary materialThe online version of this article (doi:10.1007/s00227-008-1117-6) contains supplementary material, which is available to authorized users.