Relation between phosphate and organic matter in fish-pond sediments of the Deroua fish farm (Béni-Mellal, Morocco): implications for pond management

An experimental approach of the phosphate exchange across the water–sediment interface in fish ponds of the Deroua farm (Béni-Mellal, Morocco) is needed to understand the phosphate dynamics in these ponds in relation to their water quality. During this study, we conducted experiments to determine the P-fractions of the different pond sediments and to estimate the release from these sediments of phosphate available for algal uptake. We also determined the amount of phosphate needed to saturate the sediments of two different fish ponds under anoxic and oxic conditions. Phosphate release from sediments comes mainly from Fe(OOH)P and is more important in ponds lined with sheets. The accumulation of organic matter in sediments favours the installation of anoxic conditions and enhances the phosphate release from CaCO₃P, labile in these pond sediments. Under experimental conditions, org-P plays a minor role in the P-release. Oxic conditions, to the contrary, have an inhibitory effect on the P-release from sediments. About 80–98% of the P-adsorbed onto different pond sediments was recovered in the inorg-P-fractions. Aeration induces the oxidation of FeS to Fe(OOH) which can adsorb phosphate from solution. Besides, the presence of bacteria in pond sediments was essential to promote phosphate release under anoxic conditions by controlling the oxidation state of iron and the mineralization of the organic matter. Sheet-lined ponds, when insufficiently dried, accumulate a large quantity of organic matter in their sediments. After a decrease in pH, P is released from CaCO₃P and enhances the phytoplankton productivity responsible for renewed accumulation of organic matter. Org-C concentrations in sediments over 20 mg g^–1 d.w. favour the formation of toxic factors (Fe²⁺, Mn²⁺, NO₂ ^– and H₂S) harmful for carp growth. An extended period of drying efficiently enhances the mineralization of organic matter.     

Seasonal phosphorus release from exposed,re-inundated littoral sediments of two Australian reservoirs

Water levels in many reservoirs typically fluctuate seasonally, but the effects of re-inundation of exposed sediments on nutrient dynamics in the water column are poorly known. This study concerns the seasonal differences in the potential of sediments from two Australian reservoirs, after having undergone different degrees of in situ desiccation, to release P under aerobic conditions. Differences were determined between biotic and abiotic P release, and results were also examined in relation to sediment chemistry. The two reservoirs, Carcoar Dam and Lake Rowlands, demonstrated different patterns of P release involving an interactive complex of P release mechanisms. Sediment chemistry at the reservoir margins was important because of the higher concentrations of N, P, Fe and Mn in Lake Rowlands. Physical and chemical processes influenced P uptake and release due to desiccation and oxidation of sediments and were of greater importance in Carcoar Dam. Abiotic P release from sterilised sediments was greater than from unsterilised sediments where both biotic and abiotic processes were apparent. Biotic P uptake and release were especially marked in Lake Rowlands where large macrophyte beds provided a rich source of organic matter. Little seasonal difference in P release was detected. The increased P release from dried sediments has ramifications for internal P loading into reservoirs and for the calculation of P budgets. For managers of reservoirs where large expanses of sediment are exposed during drying, it may be better to maintain high water levels, where possible, during the summer by modifying drawdown practices.     

Nitrite: a key compound in N loss processes under acid conditions?

Summary Nitrite is very important in N transformation processes because it is an intermediate product in the aerobic nitrification as well as in the anaerobic denitrification process. Under soil conditions whereby aerobic and anaerobic zones are close to each other, the mobile nitrite can be a link between both N transformation processes. Because of its low stability in acid conditions, nitrite can be a key compound in N loss processes.The results are presented in three sets of incubation experiments using soil+added nitrite before and after oxidation of organic matter; soil+added nitrite and various iron oxide minerals; nitrite solutions without soil but with added ferrous iron.It was found that under acid conditions, soil organic matter as well as the soil mineral phase have a stimulating effect on the nitrite decomposition. Conditions favouring the solubility of Fe(III)-compounds and promoting the formation of Fe²⁺ increase the nitrite decomposition, even under slightly acid conditions. Of the gaseous decomposition products, only trace amounts of NO₂ occur while NO is the major component. Conditions whereby NO and NO₂ cannot escape from the medium promote production of some nitrite.     

Microbial decomposition of organic matter in the bottom sediments of small lakes of the urban landscape (Lithuania)

Bacterial abundance and the rates of sulfate reduction (SR) and total organic matter decomposition (D_total) were studied in the bottom sediments of nine lakes in the vicinity of Vilnius (Lithuania) during the ice-free seasons of 2006–2009. During the spring mixing of the water, aerobic processes of organic matter decomposition prevailed in the bottom sediments of most lakes, while anaerobic processes predominated (up to 80–90% D_total) in summer and early autumn. SR rates in the bottom sediments made up 0.16–2.6 and 0.09–2.0 mg S^2?/(dm³ day) for the medium-depth and shallow lakes, respectively. The highest numbers of sulfate-reducing bacteria (up to 10⁶ cells/cm³) and SR rates were observed in summer. SR rate in mediumdepth lakes increased with development of anaerobic conditions at the bottom and elevated sulfate concentrations (up to 96.0 mg/dm³). In shallow lakes, where O₂ concentration at the bottom was at least 6.7 mg/L, SR rates increased with temperature and inflow of fresh organic matter, especially during cyanobacterial blooms. The average SR rates in the bottom sediments of the lakes of urbanized areas were 4 times higher than in the shallow lakes of protected areas. Accumulation of organic matter and its intensive decomposition during summer may enhance the processes of secondary eutrophication of these small and shallow lakes.     

Aerobic and anaerobic metabolism of the freshwater oligochaete Tubifex sp.

The freshwater oligochaete Tubifex shows several mechanisms of metabolic adaptations, enabling the worms to occupy saprobial habitats of extremely variable oxygen content. Under normoxic conditions the metabolism of the worms is mainly aerobic with a respiratory ratio of 0.7. Under hypoxic conditions, metabolism of energy sources via aerobic and anaerobic pathways is observed. During complete anoxia acetate and propionate are the main products of glycogen degradation and they are excreted in constant rates into the water. A retransfer of the worms to aerobic conditions enables them to regain aerobic metabolic state within about 60 min.In two Tubifex habitats, which we have characterized, concentrations of dissolved organic material (DOM) were low in the surface water, but high in the interstitial water from sediments. The short-chain fatty acids acetate and propionate reached concentrations up to 1 mmole/liter. Employing radioisotope techniques, we demonstrated that Tubifex can achieve an integumentary uptake of acetate and propionate from artificial tap water at naturally occurring concentrations of 5 to 1000 M. Levels of uptake (600 to 800 nmoles/g wwt.hr) and transport characteristics are very similar to those of marine invertebrates associated with detritus rich sediments. The uptake is susceptible to inhibition by structurally analogous compounds and to metabolic inhibition. Furthermore, DOM uptake in Tubifex is susceptible to inhibition by oxygen depletion, ouabain and Na⁺-depletion. The results may suggest that a carrier system for DOM transport exists in the integument of the worms. The uptake system is highly specific for aliphatic C2 and C3 carboxylic acids. The absorbed volatile fatty acids are rapidly metabolized. Only 15 min after absorption, a considerable amount of radioactivity is present in the glycogen storage of the animals. Depending on the substrate concentration assumed to be available for uptake, up to 40 per cent of the oxidative requirement of the worms may be attained by using dissolved organic material from the interstitial water of their habitat.Supported by the Deutsche Forschungsgemeinschaft (Ho 631/9-9).     

Organic matter diagenesis at the oxic/anoxic interface in coastal marine sediments,with emphasis on the role of burrowing animals

The present paper reviews the current knowledge on diagenetic carbon transformations at the oxic/anoxic interface in coastal marine sediments. Oxygen microelectrodes have revealed that most coastal sediments are covered only by a thin oxic surface layer. The penetration depth of oxygen into sediments is controlled by the balance between downward transport and consumption processes. Consumption of oxygen is directly or indirectly caused by respiration of benthic organisms. Aerobic organisms have the enzymatic capacity for complete oxidation of organic carbon. Anaerobic decay occurs stepwise, involving several types of bacteria. Large organic molecules are first fermented into small moieties. These are then oxidized completely by anaerobic respirers using a sequence of electron acceptors: Mn⁴⁺, NO₃ ^-, Fe³⁺, SO₄ ^2- and CO₂. The quantitative role of each electron acceptor depends on the sediment type and water depth. Since most of the sediment oxygen uptake is due to reoxidation of reduced metabolites, aerobic respiration is of limited importance. It has been suggested that sediments contain three major organic fractions: (1) fresh material that is oxidized regardless of oxygen conditions; (2) oxygen sensitive material that is only degraded in the presence of oxygen; and (3) totally refractory organic matter. Processes occurring at the oxic/anoxic boundaries are controlled by a number of factors. The most important are: (1) temperature, (2) organic supply, (3) light, (4) water currents, and (5) bioturbation. The role of bioturbation is important because the infauna creates a three-dimensional mosaic of oxic/anoxic interfaces in sediments. The volume of oxic burrow walls may be several times the volume of oxic surface sediment. The infauna increases the capacity, but not the overall organic matter decay in sediments, thus decreasing the pool of reactive organic matter. The increase in decay capacity is partly caused by injection of oxygen into the sediment, and thereby enhancing the decay of old, oxygen sensitive organic matter several fold. Finally, some future research directions to improve our understanding of diagenetic processes at the oxic/anoxic interface are suggested.     

Patern of nitrogen release during decomposition of some green manures in a tropical alluvial soil

Summary The pattern of release of ammonium and nitrate nitrogen during decomposition of glyricidia, sunflower, centrosema, calapagonium and crotolaria under aerobic and anaerobic conditions, in an alluvial soil over a period of 7 weeks was studied. Under aerobic conditions, the NH₄ ⁺–N production reached the maximum after the 4th week. Nitrate-N and total available-N increased in all cases throughout the incubation period except in sunflower. This showed a nitrification inhibitory effect and had a relatively high C/N ratio (11.0) and low total N content (2.8%). In general the increase in NH₄ ⁺–N and NO₃ ^––N was more rapid in the early stages of incubation.Under anaerobic conditions, the production of these nutrients was considerably low. Soil organic matter mineralized faster than the added organic material which started to decompose slowly after sometime. Nitrate-N tend to decrease during incubation attributable to denitrification.     

Anaerobic and aerobic oxidation of ferrous iron at neutral pH by chemoheterotrophic nitrate-reducing bacteria

Nine out of ten anaerobic enrichment cultures inoculated with sediment samples from various freshwater, brackish-water, and marine sediments exhibited ferrous iron oxidation in mineral media with nitrate and an organic cosubstrate at pH 7.2 and 30° C. Anaerobic nitrate-dependent ferrous iron oxidation was a biological process. One strain isolated from brackish-water sediment (strain HidR2, a motile, nonsporeforming, gram-negative rod) was chosen for further investigation of ferrous iron oxidation in the presence of acetate as cosubstrate. Strain HidR2 oxidized between 0.7 and 4.9 mM ferrous iron aerobically and anaerobically at pH 7.2 and 30° C in the presence of small amounts of acetate (between 0.2 and 1.1 mM). The strain gained energy for growth from anaerobic ferrous iron oxidation with nitrate, and the ratio of iron oxidized to acetate provided was constant at limiting acetate supply. The ability to oxidize ferrous iron anaerobically with nitrate at approximately pH 7 appears to be a widespread capacity among mesophilic denitrifying bacteria. Since nitrate-dependent iron oxidation closes the iron cycle within the anoxic zone of sediments and aerobic iron oxidation enhances the reoxidation of ferrous to ferric iron in the oxic zone, both processes increase the importance of iron as a transient electron carrier in the turnover of organic matter in natural sediments. Received: 24 April 1997 / Accepted: 22 September 1997     

Anaerobic mineralization of marine sediment organic matter: Rates and the role of anaerobic processes in the oceanic carbon economy

Abstract

This paper addresses three related questions: (1) What factors control the efficiency of carbon burial in sediments? (2) Are rates of anaerobic organic matter degradation intrinsically lower than aerobic rates? (3) How important are anaerobic processes in the global marine sediment carbon economy?

Carbon burial efficiency (the ratio of the carbon burial rate and the carbon flux to the sediment surface) was estimated from literature data for a range of environments and was shown to be a function of sedimentation rate. No difference independent of sedimentation rate was found between aerobic and anaerobic sediments.

A review of recent microcosm and laboratory studies shows that anaerobic rates are not intrinsically lower than aerobic rates; fresh organic matter degrades at similar rates under oxic and anoxic conditions. Aerobic decomposition rates near the sediment surface are typically greater than anaerobic rates at depth because the most labile carbon is consumed before it can be buried in the anoxic zone.

A model approach was taken in estimating the importance of anaerobic processes in the global marine sediment economy, instead of extrapolating measured rates as done previously. The result, 150 Tg C yr^?1, is two to nine times lower than previous estimates. This rate is about 9% of the global aerobic carbon oxidation rate and is about equal to the rate of long‐term carbon burial. The importance of anaerobic processes in marine sediments lies in their role in determining the amount of carbon preserved, not in the amount of carbon remineralized overall.     

Dissolved iron:phosphate ratio as an indicator of phosphate release to oxic water of the inner and outer coastal Baltic Sea

Pore water concentrations and benthic fluxes of dissolved Fe, P and N were measured at two coastal basins in the Gulf of Finland, northern Baltic Sea, during a seasonal cycle. The bioturbated inner coastal basin, where exchange of near-bottom water is efficient, had a better ability to retain P in sediments than the outer basin, where near-bottom water O₂ concentration decreases during summer. Under the presence of O₂ high pore water dissolved Fe:P ratio (>3.6 w:w) in surface layer of the sediment, measured especially in winter, indicated negligible or low P-release and high N:P ratio in the efflux. On the contrary, low Fe:P ratio (<3.6), measured in summer and autumn, indicated high efflux of P and low N:P flux ratio. The low dissolved Fe:P ratio suggested that there was not enough diffusing Fe to form Fe³⁺ oxide-rich layer in the oxic surface zone of the sediments or near-bottom water to bind the P diffusing from the sediment. However, in sediments bioturbated by the abundant bivalve Macoma baltica, small efflux of P were measured almost throughout the study period. Thus, the Fe:P ratio cannot alone explain the P-release in bioturbated sediments. The low N:P ratio in the efflux measured in summer and autumn partly explains the measured low N:P ratio in the near-bottom water and thus N limitation of primary production in the Gulf. Additionally, it is evident that the release of P in the Gulf itself is of great importance for the trophic state of the Gulf of Finland.     

Influence of submerged macrophytes on sediment composition and near-bed flow in lowland streams

1. Submerged macrophytes have important physical and structural effects on lowland streams. This study investigated the ability of submerged macrophytes to modify the near-bed flow and to retain mineral and organic particles in patches of four common macrophytes in shallow Danish streams during mid-summer. 2. In dense patches of Callitriche cophocarpa and Elodea canadensis, where near-bed velocity was reduced, the sediment surface was markedly raised and enriched with fine particles. In dense patches of Ranunculus peltatus, fine sediments were deposited among rooted shoots in the upstream part of the patches, while erosion and coarse sediments prevailed in the downstream part of the patches because of the strong vortices that formed at the rear and moved up under the trailing canopy. The open canopy of Sparganium emersum, with its streamlined leaves, had little effect on flow and sediment. 3. Patterns of sediment deposition and composition were closely related to the morphology and canopy structure of plant species and the presence of low velocity above the sediment among the rooted shoots. The mineral particles retained probably originate from bed-load, and the enrichment with finer particles within the patches probably results mainly from size-selective processes during erosion and transport of particles rather than during deposition. The mixed sediment composition within patches suggests that the flow-resistant shoots generate an environment conducive to deposition of all transported particles. 4. Fine sediments within macrophyte beds contained high concentrations of organic matter, carbon, nitrogen and phosphorus. The wide scatter in the relationships between mineral grain size and the content of organic matter and nutrients reflects the spatial and temporal complexity of erosion, transport and sedimentation of mineral and organic particles. 5. Enrichment of sediment within macrophyte beds relative to the surrounding substratum ranged from 780 g organic matter m^–2, 30 g N m^–2 and 25 g P m^–2 for the flow-resistant dense canopies af Callitriche cophocarpa to 150 g organic matter m^–2, 6.6 g N m^–2 and 3.4 g P m^–2 for the open canopies of Sparganium emersum. Retention of nutrient-rich particles within the macrophyte beds is probably of limited importance for plant growth in most lowland European streams, because macrophyte growth is rarely nutrient limited.     

The ability of aquatic macrophytes to increase root porosity and radial oxygen loss determines their resistance to sediment anoxia

Radial oxygen loss (ROL) has been suggested to be a major process to protect plants exposed to root anaerobic stress. In the present study, we aimed to test the importance of root porosity and radial oxygen loss on the aquatic macrophyte resistance to sediment anoxia. We expected that species living in eutrophic environments characterized by anaerobic conditions in sediments exhibited higher root porosity and radial oxygen loss than species restrained to oligotrophic environments. In this way, we compared the responses to sediment anoxia of two hydrophyte species growing under meso-eutrophic conditions in the field (Myriophyllum spicatum L. and Vallisneria spiralis L.) and three species growing under oligotrophic conditions (Potamogeton coloratus Horne, Elodea canadensis Michx and Sparganium emersum Michx.). Under laboratory conditions, ROL, root porosity, plant metabolism (aerobic respiration, photosynthesis, root fermentative activity) and plant growth were analysed after 3?months of acclimation in anaerobic sediments and compared with control values obtained from aerobic sediments. The results showed that two meso-eutrophic species (M. spicatum and V. spiralis) survived in anaerobic sediments and maintained similar photosynthesis rates than those measured under aerobic conditions. In contrast, the three oligotrophic species (P. coloratus, E. canadensis and S. emersum) suffered net biomass loss and depressed their photosynthesis rates under anaerobic conditions. All variables associated with plant tolerance to anaerobic conditions (maintenance of photosynthesis, aerobic respiration and growth rate, and limitation of root fermentative activity) were positively linked to root porosity and ROL. According to our hypothesis, species that could survive to anaerobic conditions were the species able to increase their root porosity and ROL under these conditions. Thus, in ecological studies, it would be useful to use the root porosity and ROL plasticity as biological traits in order to model the distribution of macrophytes in river floodplains.     

Impact of chemical composition of legume residues and initial soil pH on pH change of a soil after residue incorporation

Reports on the effect of organic matter addition on soil pH have been contradictory. This study examined the effect of applying legume residues differing in concentrations of N (4.3-45.5 mg g^-1) and excess cations/organic anions (0.22–1.56 mmol g^-1) on pH change of five soils differing in initial pH (3.60–5.58 in 0.01 M CaCl₂) under sterile and non-sterile conditions. Addition of the legume residues at a level of 1% soil weight increased the pH of all soils by up to 2 units after incubation for 35 and 100 d under non-sterile conditions. Exceptions were the Lancelin (initial pH 5.06) and Kellerberin (pH 5.58) soils with addition of clover roots (excess cations 22 cmol/kg) for 100 d where soil pH decreased by 0.13–0.15 units as compared to the control. The amounts of alkalinity produced in soil correlated positively with concentrations of excess cations and total nitrogen of the added legume residues, and negatively with the initial pH of the soil. When soil was fumigated with chloroform during incubation, similar trends of soil pH changes and alkalinity production, due to legume residues addition, were displayed but the effects of the residue on alkalinity production in the Wodjil and Lancelin soils were much less than under non-sterile conditions. Direct shaking of soil with the residues under sterile conditions increased the amount of alkalinity in the soils with initial pH of 3.60–4.54, but not in the soils with initial pH of 5.06 and 5.58. The maximal alkalinity production was less than one third of that produced in the soil after 100 d of incubation under non-sterile conditions. The results suggest that the direction and the magnitude of pH change depend largely on the concentration of organic anions in the residues, initial soil pH and the degree of residue decomposition. The incorporation of crop residues, especially those with high concentrations of excess cations, is recommended in minimizing soil acidification in farming systems. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nuclear Magnetic Resonance Studies of Poly(3-Hydroxybutyrate) and Polyphosphate Metabolism in Alcaligenes eutrophus

The metabolic pathways of poly(3-hydroxybutyrate) (PHB) and polyphosphate in the microorganism Alcaligenes eutrophus H16 were studied by ¹H, ¹³C, and ³¹P nuclear magnetic resonance (NMR) spectroscopy and by conventional analytical techniques. A. eutrophus cells accumulated two storage polymers of PHB and polyphosphate in the presence of carbon and phosphate sources under aerobic conditions after exhaustion of nitrogen sources. The solid-state cross-polarization/magic-angle spinning ¹³C NMR spectroscopy was used to study the biosynthetic pathways of PHB and other cellular biomass components from ¹³C-labeled acetate. The solid-state ¹³C NMR analysis of lyophilized intact cells grown on [1-¹³C]acetate indicated that the carbonyl carbon of acetate was selectively incorporated both into the carbonyl and methine carbons of PHB and into the carbonyl carbons of proteins. The ³¹P NMR analysis of A. eutrophus cells in suspension showed that the synthesis of intracellular polyphosphate was closely related to the synthesis of PHB. The roles of PHB and polyphosphate in the cells were studied under conditions of carbon, phosphorus, and nitrogen source starvation. Under both aerobic and anaerobic conditions PHB was degraded, whereas little polyphosphate was degraded. The rate of PHB degradation under anaerobic conditions was faster than that under aerobic conditions. Under anaerobic conditions, acetate and 3-hydroxybutyrate were produced as the major extracellular metabolites. The implications of this observation are discussed in connection with the regulation of PHB and polyphosphate metabolism in A. eutrophus.     

On the Problem of Anaerobic Methane Oxidation

To clarify the biological mechanism of anaerobic methane oxidation, experiments were performed with samples of the Black Sea anaerobic sediments and with the aerobic methane-oxidizing bacterium Methylomonas methanica strain 12. The inhibition–stimulation analysis did not allow an unambiguous conclusion to be made about a direct and independent role of either methanogenic or sulfate-reducing microorganisms in the biogeochemical process of anaerobic methane oxidation. Enrichment cultures obtained from samples of water and reduced sediments oxidized methane under anaerobic conditions, primarily in the presence of acetate or formate or of a mixture of acetate, formate, and lactate. However, this ability was retained by the cultures for no more than two transfers on corresponding media. Experiments showed that the aerobic methanotroph Mm. methanica strain 12 is incapable of anaerobic methane oxidation at the expense of the reduction of amorphous FeOOH.     

Acetogenic Capacities and the Anaerobic Turnover of Carbon in a Kansas Prairie Soil

To assess the anaerobic capacities of a temperate grassland soil, a Kansas prairie soil was incubated anaerobically as either soil-water (1:2) suspensions or as soil microcosms at 78% soil water-holding capacity. Prairie soil formed acetate and CO(inf2) as the two main initial carbonaceous products from the anaerobic turnover of endogenous organic matter. Metabolic capacities of soil suspensions and microcosms were similar. Rates of acetate formation from endogenous organic matter in soil-water suspensions incubated at 40, 30, and 15(deg)C approximated 3.3, 2.4, and 1.1 (mu)g of acetate per g (dry weight) of soil per h, respectively. Supplemental H(inf2) and CO(inf2) were subject to consumption with the apparent concomitant synthesis of acetate in both soil suspensions and soil microcosms. In soil microcosms, rates of H(inf2)-dependent acetogenesis at 30 and 55(deg)C were nearly equivalent. The uptake of supplemental H(inf2) was not coupled to methanogenesis under any condition examined. These anaerobic activities were relatively stable when soils were subjected to either aerobic drying or alternating periods of O(inf2) enrichment. On the basis of the formation of nitrogen (N(inf2)), denitrification was engaged during anaerobic incubation periods; nitrous oxide (N(inf2)O) was also formed under certain conditions. Although extended incubation of soil induced the delayed methanogenic turnover of acetate, acetate was subject to immediate turnover under either O(inf2)- or nitrate-enriched conditions. These studies support the following concepts: (i) obligately anaerobic bacteria such as acetogenic bacteria are stable to periods of aerobiosis and are active in the anaerobic microsites of oxic soils, and (ii) acetate synthesized in anaerobic microsites of oxic terrestrial soils constitutes a trophic link to both aerobic and anaerobic microbial communities.     

Anaerobically grown <Emphasis Type="Italic">Thauera aromatica</Emphasis>, <Emphasis Type="Italic">Desulfococcus multivorans</Emphasis>, <Emphasis Type="Italic">Geobacter sulfurreducens</Emphasis> are more sensitive towards organic solvents than aerobic bacteria

The effect of seven important pollutants and three representative organic solvents on growth of Thauera aromatica K172, as reference strain for nitrate-reducing anaerobic bacteria, was investigated. Toxicity in form of the effective concentrations (EC50) that led to 50% growth inhibition of potential organic pollutants such as BTEX (benzene, toluene, ethylbenzene, and xylene), chlorinated phenols and aliphatic alcohols on cells was tested under various anaerobic conditions. Similar results were obtained for Geobacter sulfurreducens and Desulfococcus multivorans as representative for Fe³⁺-reducing and sulphate-reducing bacteria, respectively, leading to a conclusion that anaerobic bacteria are far more sensitive to organic pollutants than aerobic ones. Like for previous studies for aerobic bacteria, yeast and animal cell cultures, a correlation between toxicity and hydrophobicity (log P values) of organic compounds for different anaerobic bacteria was ascertained. However, compared to aerobic bacteria, all three tested anaerobic bacteria were shown to be about three times more sensitive to the tested substances.     

Metabolism of organic compounds in anaerobic,hydrothermal sulphate-reducing marine sediments

Previous studies of hot (>80 degrees C) microbial ecosystems have primarily relied on the study of pure cultures or analysis of 16S rDNA sequences. In order to gain more information on anaerobic metabolism by natural communities in hot environments, sediments were collected from a shallow marine hydrothermal vent system in Baia di Levante, Vulcano, Italy and incubated under strict anaerobic conditions at 90 degrees C. Sulphate reduction was the predominant terminal electron-accepting process in the sediments. The addition of molybdate inhibited sulphate reduction in the sediments and resulted in a linear accumulation of acetate and hydrogen over time. [U-14C]- acetate was completely oxidized to 14CO2, and the addition of molybdate inhibited 14CO2 production by 60%. [U-14C]-glucose was oxidized to 14CO2, and this was inhibited when molybdate was added. When the pool sizes of short-chain fatty acids were artificially increased, radiolabel from [U-14C]-glucose accumulated in the acetate pool. L-[U-14C]-glutamate, [ring-14C]-benzoate and [U-14C]-palmitate were also anaerobically oxidized to 14CO2 in the sediments, but molybdate had little effect on the oxidation of these compounds. These results demonstrate that natural microbial communities living in a hot, microbial ecosystem can oxidize acetate and a range of other organic electron donors under sulphate-reducing conditions and suggest that acetate is an important extracellular intermediate in the anaerobic degradation of organic matter in hot microbial ecosystems.     

Aerobic and anaerobic microbial activity in deep subsurface sediments from the savannah river plant

Methanogenesis, sulfate reduction, and rates of carbon mineralization were determined for samples derived at different depths from four cores drilled at the Savannah River Plant, Aiken South Carolina. Three‐gram subsamples of the sediments were dispensed to 10‐mL serum bottles under 5% H₂/95% N₂ and amended with 0.5 mL degassed distilled water with or without the following solutes: formate plus acetate, bicarbonate, lactate, and radiolabeled sulfate, glucose, and Índole. After incubating 1 to 5 days, the sediments were assayed for methane, H₂, ³⁵S, and ^I4CO₂. No methanogenesis was detected at any depth in any core and sulfate was rarely reduced. Evolution of ¹⁴CO₂ from glucose and indole was detected in sediments as deep as 262 and 259 m, respectively. At some depths the ¹⁴CO₂ evolution rate was comparable to that of surface soils; however, at other depths no ¹⁴CO₂ evolution could be detected. Injection of sterile air into anaerobic incubations increased rates of carbon mineralization at all depths that had demonstrated anaerobic activity and stimulated mineralization activity in sediments that were inactive anaerobically, suggesting a predominance of aerobic metabolism. Increasing the concentration of added glucose and indole often increased the resulting rates of ¹⁴CO₂ evolved from these substrates. Our data indicate that both aerobic and anaerobic microorganisms are present and metabolically active in samples from deep subsurface environments.