Acetogenesis and acetotrophy in a hexanoate-catabolizing microbial association isolated from anoxic landfill

Metabolism of the key intermediates, acetate and hydrogen, in anaerobic hexanoate catabolism by an interacting microbial association isolated from a landfill was examined in the presence of sulphate. Hydrogen (the β-oxidation product of hexanoate and butyrate), was competitively utilized by the component sulphate-reducing bacteria whereas in the absence of sulphate an interaction between H₂-utilizing acetogenic and methanogenic bacteria facilitated H₂ removal, with acetate catabolism restricted to methanogenic bacteria. A possible mechanism for energy conservation was suggested in which excess electrons were stored as acetate for subsequent usage as an energy source.     

Competition for hydrogen between sulphate-reducing bacteria and methanogenic bacteria from the human large intestine

Sulphate-reducing activity in human faecal slurries was followed by measuring sulphide production. Sulphate-reducing bacteria (SRB) were found to outcompete methanogenic bacteria (MB) for the mutual substrate hydrogen in faecal slurries from methane- and non-methane-producing individuals mixed together. When molybdate (20 mmol/l) was added to these slurries, sulphate reduction was inhibited and methanogenesis became the major route of electron disposal. Sulphide production was stimulated by the addition of 20 mmol/l sulphate in non-methanogenic but not in methanogenic slurries. In methanogenic slurries that contained the methanogen inhibitor 2-bromoethanesulphonic acid (BES), hydrogen accumulated whilst sulphide levels were unaffected, confirming the absence of SRB in methanogenic faeces. The addition of nitrate (10 mmol/l) to faecal slurries completely inhibited methanogenesis but only slightly reduced sulphate reduction. The sulphated mucopolysaccharides, chondroitin sulphate and mucin, strongly stimulated sulphide production in non-methanogenic faecal slurries only, suggesting that these substances may be a potential source of sulphate in the large gut.     

Competition for hydrogen between sulphate-reducing bacteria and methanogenic bacteria from the human large intestine

Sulphate-reducing activity in human faecal slurries was followed by measuring sulphide production. Sulphate-reducing bacteria (SRB) were found to outcompete methanogenic bacteria (MB) for the mutual substrate hydrogen in faecal slurries from methane- and non-methane-producing individuals mixed together. When molybdate (20mmol/l) was added to these slurries, sulphate reduction was inhibited and methanogenesis became the major route of electron disposal. Sulphide production was stimulated by the addition of 20 mmol/1 sulphate in non-methanogenic but not in methanogenic slurries. In methanogenic slurries that contained the methanogen inhibitor 2-bromoethanesulphonic acid (BES), hydrogen accumulated whilst sulphide levels were unaffected, confirming the absence of SRB in methanogenic faeces. The addition of nitrate (10 mmol/l) to faecal slurries completely inhibited methanogenesis but only slightly reduced sulphate reduction. The sulphated mucopolysaccharides, chondroitin sulphate and mucin, strongly stimulated sulphide production in non-methanogenic faecal slurries only, suggesting that these substances may be a potential source of sulphate in the large gut.     

Effects of phenol wastewater co-disposal, on the attenuation of the refuse leachate molecule hexanoic acid

A three-stage continuous culture model system was used to investigate the impacts of increasing concentrations of phenol on the component physiological groups of a hexanoate-catabolizing association, isolated from anoxic landfill. Low concentrations (2 mmol/1) were found to reduce sulphate-reducing bacterial activity whilst concentrations of 8 and 22 mmol/1 effected reductions of 90·2 and 99·1% in methane release rate and hexanoate β-oxidation, respectively.     

Evaluation of relative importance of different microbial reactions on organic matter removal in horizontal subsurface-flow constructed wetlands using a 2D simulation model

In this study, we used a two-dimensional (2D) mechanistic mathematical model in order to evaluate the relative contribution of different microbial reactions to organic matter removal (in terms of COD) in horizontal subsurface-flow constructed wetlands that treated urban wastewater. We also used the model to analyse the effect of increasing or decreasing the organic loading rate (changing the hydraulic loading rate (HLR) at a constant influent organic matter concentration, or changing the organic matter concentration at a constant HLR) on both the removal efficiency and the relative importance of the microbial reactions. The model is based on the code RetrasoCodeBright, which we modified to include the main microbial processes related to organic matter and nitrogen transformations in the wetlands: hydrolysis, aerobic respiration, nitrification, denitrification, sulphate reduction and methanogenesis. The model was calibrated and validated with data from two wetlands (each with a surface area of 55 m²) located in a pilot plant near Barcelona (Spain). According to the simulations, anaerobic processes (methanogenesis and sulphate reduction) are more widespread in the wetlands and contribute to a higher COD removal rate (60–70%) than anoxic (denitrification) and aerobic reactions do. These model results are confirmed by experimental observations. In all the cases tested, the reaction that most contributed to COD removal was methanogenesis (33–52%). According to our simulations, decreasing the HLR (for example, from 40 to 25 mm/d) while maintaining a constant COD influent concentration has a clear positive impact on COD removal efficiency (which increases from 65% to 89%). Changing influent COD concentration (for example, from 290 to 190 mg/L) while maintaining a constant HLR has a smaller impact, causing efficiency to increase from 79% to 84%. Changes in influent COD concentration (at a constant HLR) affect the relative contribution of the microbial reactions to organic matter removal. However, this trend is not seen when the HLR changes and the COD influent concentration remains constant.     

9-Aminoacridine- and tetraethylammonium-induced reduction of the potassium permeability in pancreatic B-cells. Effects on insulin release and electrical properties.

The effects of 9-aminoacridine and tetraethylammonium on insulin release and rubidium efflux from perifused rat islets were investigated and correlated with their effects on the electrical properties of mouse B cells studied with microelectrode techniques. 9-Aminoacridine (0.05--1 mmol/l) and tetraethylammonium (2--40 mmol/l) produced a dose-dependent, reversible potentiation of glucose-stimulated insulin release. This effect was rapid, affected both phases of secretion and was maximum in the presence of 6 mmol/l glucose, but no longer significant at 20 mmol/l glucose. It was unaltered by atropine or propanolol, and abolished by mannoheptulose or omission of extracellular calcium. 9-Aminoacridine, but not tetraethylammonium, also induced insulin release in the absence of glucose stimulation. Neither drug modified glucose metabolism in islet cells and only 9-aminoacridine increased 45Ca2+ uptake. In the presence of 0, 3 or 6 mmol/l glucose, but no longer at 20 mmol/l glucose, 9-aminoacridine and tetraethylammonium reduced the rate of 86Rb+ efflux from the islets. Both drugs also slightly reduced 86Rb+ uptake by islet cells. In the presence of 11 mmol/l glucose, 9-aminoacridine reduced the amplitude and the duration of the polarization phases between the bursts of electrical activity; concomitantly these periods of spike activity were markedly prolonged. At lower glucose concentrations (3 or 7 mmol/l), 9-aminoacridine progressively depolarized B cells and induced electrical activity in otherwise silent cells. Tetraethylammonium also suppressed the repolarization phases between the bursts of spikes in the presence of a stimulating concentration of glucose. At low glucose, tetraethylammonium produced only a limited and not maintained depolarization. These results show that a reduction of the potassium permeability in pancreatic B cells potentiates the insulin-releasing effect of glucose and may even stimulate secretion. They also suggest that the initial depolarizing effect of glucose is due to a reduction of the potassium permeability, whereas the repolarization at the end of each burst of electrical activity is mediated, at least in part, by an increase in the potassium permeability of B cells.     

Microbial diversity and activity in seafloor brine lake sediments (Alaminos Canyon block 601, Gulf of Mexico)

The microbial communities thriving in deep‐sea brines are sustained largely by energy rich substrates supplied through active seepage. Geochemical, microbial activity, and microbial community composition data from different habitats at a Gulf of Mexico brine lake in Alaminos Canyon revealed habitat‐linked variability in geochemistry that in turn drove patterns in microbial community composition and activity. The bottom of the brine lake was the most geochemically extreme (highest salinity and nutrient concentrations) habitat and its microbial community exhibited the highest diversity and richness indices. The habitat at the upper halocline of the lake hosted the highest rates of sulfate reduction and methane oxidation, and the largest inventories of dissolved inorganic carbon, particulate organic carbon, and hydrogen sulfide. Statistical analyses indicated a significant positive correlation between the bacterial and archaeal diversity in the bottom brine sample and inventories. Other environmental factors with positive correlation with microbial diversity indices were DOC, H₂S, and DIC concentrations. The geochemical regime of different sites within this deep seafloor extreme environment exerts a clear selective force on microbial communities and on patterns of microbial activity.     

Human placental glutathione transferase: interactions with steroids

Glutathione transferases exhibit both isomerase and transferase activity. The acceptance of steroids as substrates for or inhibitors of these activities was studied using a 350-fold enriched preparation of the enzyme from human placenta. As an isomerase, the enzyme preparation catalyzed the conversion of pregn-5-ene-3,20-dione (Km 0.03 mmol/l) and androst-5-ene-3,17-dione (Km 0.05 mmol/l) to the respective 4-ene-3-oxosteroids (specific activity 0.8 U/mg protein). This isomerase activity strictly depended on the presence of glutathione (Km 0.04 mmol/l). As a transferase, the enzyme preparation catalyzed the conjugation of glutathione (Km 0.5 mmol/l) with 1-chloro-2,4-dinitrobenzene (Km 1.0 mmol/l) (specific activity 100 U/mg protein). This transferase activity was inhibited by all phenolic (KI values 0.2-1.5 mmol/l) and some of the neutral steroids (KI values 1.4-3.5 mmol/l) tested. Phenolic steroids inhibited the enzyme activity competitively to 1-chloro-2,4-dinitrobenzene and non-competitively to both substrates. The results indicate that steroids can interact with the placental glutathione transferase in vitro both as substrates and as inhibitors. Since, however, the observed Km and KI values of the steroids are far above the values of their concentrations in the placenta, these interactions are of only minor physiological relevance.     

9-aminoacridine- and tetraethylammonium -induced reduction of the potassium permeability in pancreatic B-cells: Effects on insulin release and electrical properties

The effects of 9-aminoacridine and tetraethylammonium on insulin release and rubidium efflux from perifused rat islets were investigated and correlated with their effects on the electrical properties of mouse B cells studied with microelectrode techniques. 9-Aminoacridine (0.05–1 mmol/1) and tetraethylammonium (2–40 mmol/l) produced a dose-dependent, reversible potentiation of glucose-stimulated insulin release. This effect was rapid, affected both phases of secretion and was maximum in the presence of 6 mmol/l glucose, but no longer significant at 20 mmol/l glucose. It was unaltered by atropine or propanolol, and abolished by mannoheptulose or omission of extracellular calcium. 9-Aminoacridine, but not tetraethylammonium, also induced insulin release in the absence of glucose stimulation. Neither drug modified glucose metabolism in islet cells and only 9-aminoacridine increased ⁴⁵Ca²⁺ uptake. In the presence of 0, 3 or 6 mmol/l glucose, but no longer at 20 mmol/l glucose, 9-aminoacridine and tetraethylammonium reduced the rate of ⁸⁶Rb⁺ efflux from the islets. Both drugs also slightly reduced ⁸⁶Rb⁺ uptake by islet cells. In the presence of 11 mmol/l glucose, 9-aminoacridine reduced the amplitude and the duration of the polarization phases between the bursts of electrical activity; concomitantly these periods of spike activity were markedly prolonged. At lower glucose concentrations (3 or 7 mmol/l), 9-aminoacridine progressively depolarized B cells and induced electrical activity in otherwise silent cells. Tetraethylammonium also suppressed the repolarization phases between the bursts of spikes in the presence of a stimulating concentration of glucose. At low glucose, tetraethylammonium produced only a limited and not maintained depolarization.These results show that a reduction of the potassium permeability in pancreatic B cells potentiates the insulin-releasing effect of glucose and may even stimulate secretion. They also suggest that the initial depolarizing effect of glucose is due to a reduction of the potassium permeability, whereas the repolarization at the end of each burst of electrical activity is mediated, at least in part, by an increase in the potassium permeability of B cells.     

Changes in metabolism of the rumen bacterium Streptococcus bovis H13/1 resulting from alteration in dilution rate and glucose supply per unit time

Streptococcus bovis H13/1 was grown in a glucose-limited chemostat. A concomitant increase in dilution rate and glucose supply per unit time caused both an increase in lactate production per mole of glucose fermented and a linear increase in growth yield over the dilution rate range 0.052 to 0.141/h. When the dilution rate was increased with no change in glucose supply per unit time there was a reduction in lactate production and an increase in that of acetate and ethanol coinciding with a non-linear increase in growth yield. YMaxglu = 38.6 and a maintenance coefficient, ms = 0.290 mmol/l glucose/g cells/h were calculated. The results also suggested an interaction between the formate and CO2 pools.     

Proteoglycan inhibition of calcium phosphate precipitation in liposomal suspensions.

The major proteoglycan in cartilage (aggrecan) is a complex macromolecule with numerous chondroitin sulphate, keratan sulphate, and oligosaccharide substituents. It has been proposed that this macromolecule has an important role in regulating mineralization in this tissue, a process which is initiated by the deposition of apatite in matrix vesicles. We have used a liposome-centred endogenous precipitation method as a model for matrix vesicle mineralization to study the effect of the rat chondrosarcoma aggrecan and its chondroitin sulphate and core protein components on apatite formation from solution. Precipitation was initiated by encapsulating buffered (pH 7.4) 50 mmol/l KH2PO4 solutions in the aqueous centres of 7:2:1 phosphatidylcholine:dicetylphosphate:cholesterol liposomes, adding 2.25-2.65 mmol/l Ca2+ and 1.5 mmol/l total inorganic phosphate (PO4) to the suspending medium (pH 7.4, 22 degrees C), then making the intervening lipid membranes permeable to the Ca2+ ions with the calcium ionophore X-537A. Aggrecan (0.5%) in the suspending medium had no effect on intraliposomal precipitation, but severely reduced (approximately 70% reduction at 24 h) its subsequent spread into the medium. The chondroitin sulphate and core protein were similarly inhibitory. The degree to which aggrecan and its constituent parts inhibited precipitation correlated with their capacity to bind Ca2+ ions. These findings suggest that functional groups in aggrecan blocked apatite growth by linking via Ca2+ bridges to growth sites on the crystal surfaces. Similar Ca-mediated interactions may well have a critical regulatory role in cartilage mineralization.     

Changes in metabolism of the rumen bacterium Streptococcus bovis H13/1 resulting from alteration in dilution rate and glucose supply per unit time

Streptococcus bovis H13/1 was grown in a glucose-limited chemostat. A concomitant increase in dilution rate and glucose supply per unit time caused both an increase in lactate production per mole of glucose fermented and a linear increase in growth yield over the dilution rate range 0.052 to 0.141/h. When the dilution rate was increased with no change in glucose supply per unit time there was a reduction in lactate production and an increase in that of acetate and ethanol coinciding with a non-linear increase in growth yield. Y_glu^Max= 38.6 and a maintenance coefficient, m_s= 0.290 mmol/l glucose/g cells/h were calculated. The results also suggested an interaction between the formate and CO₂ pools.     

气提式内循环硝化反应器运行性能的研究

气提式内循环反应器具有很好的生物硝化性能,能承受高进水氨浓度（78.49mmol/L）,具有高容积转化效率（163.18 mmol/L·d）,运行性能稳定（氨去除率保持在94.42%以上）。在气提式内循环反应器的运行过程中,可产生硝化颗粒污泥。颗粒污泥开始出现的时间约为45d,颗粒污泥的粒径平均值0.83 mm,沉降速度55.53m/h,氨氧化活性0.95mmol (NH⁺₄-N)/g(VS)·d。硝化颗粒污泥也具有厌氧氨氧化活性,氨氧化速率0.23mmol (NH⁺₄-N)/g(VS)·d,亚硝酸还原速率0.24mmol (NO^-₂-N)/g(VS)·d。     

Control of hepatic nitrogen metabolism and glutathione release by cell volume regulatory mechanisms

1. Urea synthesis was studied in isolated perfused rat liver during cell volume regulatory ion fluxes following exposure of the liver to anisotonic perfusion media. Lowering of the osmolarity in influent perfusate from 305 mOsm/l to 225 mOsm/l (by decreasing influent [NaCl] by 40 mmol/l) led to an inhibition of urea synthesis from NH4Cl (0.5 mmol/l) by about 60% and a decrease of hepatic oxygen uptake by 0.43 +/- 0.03 mumol g-1 min-1 [from 3.09 +/- 0.13 mumol g-1 min-1 to 2.66 +/- 0.12 mumol g-1 min-1 (n = 9)]. The effects on urea synthesis and oxygen uptake were observed throughout hypotonic exposure (225 mOsm/l). They persisted although volume regulatory K+ efflux from the liver was complete within 8 min and were fully reversible upon reexposure to normotonic perfusion media (305 mOsm/l). A 42% inhibition of urea synthesis from NH4Cl (0.5 mmol/l) during hypotonicity was also observed when the perfusion medium was supplemented with glucose (5 mmol/l). Urea synthesis was inhibited by only 10-20% in livers from fed rats, and was even stimulated in those from starved rats when an amino acid mixture (twice the physiological concentration) plus NH4Cl (0.2 mmol/l) was infused. 2. The inhibition of urea synthesis from NH4Cl (0.5 mmol/l) during hypotonicity was accompanied by a threefold increase of citrulline tissue levels, a 50-70% decrease of the tissue contents of glutamate, aspartate, citrate and malate, whereas 2-oxoglutarate, ATP and ornithine tissue levels, and the [3H]inulin extracellular space remained almost unaltered. Further, hypotonic exposure stimulated hepatic glutathione (GSH) release with a time course roughly paralleling volume regulatory K+ efflux. NH4Cl stimulated lactate release from the liver during hypotonic but not during normotonic perfusion. In the absence of NH4Cl, hypotonicity did not significantly affect the lactate/pyruvate ratio in effluent perfusate. With NH4Cl (0.5 mmol/l) present, the lactate/pyruvate ratio increased from 4.3 to 8.2 in hypotonicity, whereas simultaneously the 3-hydroxybutyrate/acetoacetate ratio slightly, but significantly decreased. 3. Addition of lactate (2.1 mmol/l) and pyruvate (0.3 mmol/l) to influent perfusate did not affect urea synthesis in normotonic perfusions, but completely prevented the inhibition of urea synthesis from NH4Cl (0.5 mmol/l) induced by hypotonicity. Restoration of urea production in hypotonic perfusions by addition of lactate and pyruvate was largely abolished in the presence of 2-cyanocinnamate (0.5 mmol/l). Addition of 3-hydroxybutyrate (0.5 mmol/l), but not of acetoacetate (0.5 mmol/l) largely reversed the hypotonicity-induced inhibition of urea synthesis from NH4Cl.(ABSTRACT TRUNCATED AT 400 WORDS)     

Insights into the structure/function of hepatocyte growth factor/scatter factor from studies with individual domains

Hepatocyte growth factor/scatter factor (HGF/SF), the ligand for the receptor tyrosine kinase encoded by the c-Met proto-oncogene, is a multidomain protein structurally related to the pro-enzyme plasminogen and with major roles in development, tissue regeneration and cancer. We have expressed the N-terminal (N) domain, the four kringle domains (K1 to K4) and the serine proteinase homology domain (SP) of HGF/SF individually in yeast or mammalian cells and studied their ability to: (i) bind the Met receptor as well as heparan sulphate and dermatan sulphate co-receptors, (ii) activate Met in target cells and, (iii) map their binding sites onto the beta-propeller domain of Met. The N, K1 and SP domains bound Met directly with comparable affinities (K(d)=2.4, 3.3 and 1.4 microM). The same domains also bound heparin with decreasing affinities (N>K1>SP) but only the N domain bound dermatan sulphate. Three kringle domains (K1, K2 and K4) displayed agonistic activity on target cells. In contrast, the N and SP domains, although capable of Met binding, displayed no or little activity. Further, cross-linking experiments demonstrated that both the N domain and kringles 1-2 bind the beta-chain moiety (amino acid residues 308-514) of the Met beta-propeller. In summary, the K1, K2 and K4 domains of HGF/SF are sufficient for Met activation, whereas the N and SP domains are not, although the latter domains contribute additional binding sites necessary for receptor activation by full length HGF/SF. The results provide new insights into the structure/function of HGF/SF and a basis for engineering the N and K1 domains as receptor antagonists for cancer therapy.     

A flow cytometry analysis of batch and continuous culture transient diauxic growth in Hansenula polymorpha

A flow cytometry analysis and in vitro enzyme activity study is carried out on the methylotrophic yeast, Hansenula polymorpha, during both (a) batch growth and (b) continuous cultures subjected to single perturbations in either system dilution rate or influent carbon substrate composition. Flow cytometry of yeasts growing diauxically on a glucose: methanol mixture during exponential growth, exhibit DNA and RNA distributions indicative of the S-synthesis-phase of the cell cycle. Cells at the stationary growth stage exhibit DNA and RNA distributions that indicate one portion of the population in the G ₀/G₁ resting phase and another in the M-mitosis-phase.Yeast cells grown at a steady-state of D=0.2 h¹, then shifted to D=0.35 h^–1, at a constant influent substrate mixture, are also examined with both flow cytometry and in vitro enzyme assays. Distributions of DNA, RNA, and total protein at either steady state and during the shift between dilution rates did not resemble any observed in batch culture. Flow cytometry indicates significant changes in cell composition within 20 min of the imposed dilution rate shift. In vitro enzyme assays show a response time in decreasing methanol oxidase activity of 2.5–3 h upon a dilution rate shift-up, while hexokinase activity increases to its steady-state level in less than 3 h. Similar cell compositional changes are reported for shifts in influent substrate methanol: glucose ratio at a constant dilution rate of D=0.35 h ^–1. Results suggest that an unsteady-state regime, oscillating between conditions that promote maximum enzyme activity of either glucose- or methanol-metabolizing enzymes, may allow simultaneous enhanced time-averaged production of both sets of enzymes.     

Effects of nitroglycerin on energy metabolism of rat reticulocytes.

Nitric oxide (NO) in many cells inactivates aconitase and mitochondrial respiratory chain, and influenced glyceraldehyde 3-phosphate dehydrogenase activity. The aim of this study was to evaluate role of nitroglycerin (NTG), a widely used NO donor, on energy metabolism of rat reticulocytes. Rat reticulocyte rich red blood cell suspensions containing 70-100% of reticulocytes, were aerobically incubated without (control) or in the presence of different concentrations of (a) NTG (0.1, 0.25, 0.5, 1.0, 1.5 mmol/l), (b) 8-Br-cGMP (0.1, 0.5, 1.0 mmol/l) and (c) NaNO2 and NaNO3 (1 mmol/l). NTG in dose- and time-dependent manner decreased total (p>0.05; EC50 = 0.78+/-0.05 mmol/l) and coupled (p<0.05; EC50 = 0.50+/-0.04 mmol/l) and increased uncoupled oxygen consumption (p<0.05: EC50 = 0.36+/-0.01 mmol/l). They were accompanied by stimulation of glycolysis, as measured by increased glucose consumption and lactate accumulation (p<0.001 EC50 = 0.53 and 0.53 mmol/l, respectively). Levels of all glycolytic intermediates in the presence of NTG indicate stimulation of HK-PFK, GA3PDH and PK activity. NTG significantly decreased ATP level, which accompanied by increased ADP and AMP levels. However, level of total adenine nucleotides (TAN) was significantly lower, which was consequence of increased catabolism of adenine nucleotides (increased hypoxanthine level; p<0.05). Stimulation of glycolysis accompanied with inhibition of the OxP, activation of HK-PFK, decrease of ATP and simultaneous rise of ADP and AMP levels, all together represent an example of Pasteur effect occurring in NTG-treated reticulocytes. In rat reticulocytes under steady state conditions 93% of overall energy was produced by OxP, but only 7% by glycolysis. Due to decrease of coupled oxygen consumption in the presence of NTG, ATP production via OxP was significantly diminished. Simultaneous increase of glycolytic ATP production is not enough to provide constant either ATP production or concentration. Calculated mean ATP-turnover time was prolonged even for 45% in the presence of 1.5 mmol/l NTG. Metabolic effects of NTG were not mimic by exogenous 8-Br-cGMP, NaNO2 or NaNO3, which indicate that NTG induced a) inhibition of coupled respiration and b) stimulation of glycolysis in rat reticulocytes are mediated by NO as an effector molecule.     

Sulphate reduction and sulphur cycling in lake sediments: a review

1. The concentration of sulphate is low in lakes and sulphur cycling has often been neglected in studies of organic matter diagenesis in lake sediments. The cycling of sulphur is, however, both spatially and temporally dynamic and strongly influences many biogeochemical reactions in sediments, such as the binding of phosphorus. This review examines the control of sulphate reduction and sulphur cycling in sediments of lakes with different trophic status. 2. The factors that control the rate of sulphate reduction have not been identified with certainty in the various environments because many factors are involved, e.g. oxygen and sulphate concentrations, temperature and organic matter availability. 3. Sulphate reduction is less significant under oligotrophic conditions, where mineralization is dominated by oxic decomposition. The supply of organic matter may not be sufficient to support sulphate reduction in the anoxic parts of sediments and, also, sulphate availability may control the rate as the concentration is generally low in oligotrophic lakes. 4. There is a potential for significant sulphate reduction in eutrophic lakes, as both the availability of organic matter and sulphate concentration are often higher than in oligotrophic lakes. Sulphate is rapidly depleted with sediment depth, however, and methanogenesis is generally the most important process in overall carbon mineralization. Sulphate reduction is generally low in acidic lakes because of low sulphate availability and reduced microbial activity. 5. It is still unclear which of the forms of sulphur deposits are the most important and under which conditions burial occurs. Sulphur deposition is controlled by the rate of sulphate reduction and reoxidation. Reoxidation of sulphides occurs rapidly through several pathways, both under oxic and anoxic conditions. Only a few studies have been able to examine the importance of reoxidation, but it is hypothesized that most of the reoxidation takes place under anoxic conditions and that disproportionation is often involved. The presence of sulphide oxidizing bacteria, benthic fauna and rooted macrophytes may substantially enhance oxic reoxidation. Deposition of sulphur is generally higher in eutrophic than in oligotrophic lakes because of a number of factors: a higher rate of sulphate reduction, enhanced sedimentation of organic sulphur and less reoxidation as a result of reduced penetration of oxygen into the sediments, a lack of faunal activity and rooted macrophytes.     

Transient behavior of a continuous stirred tank biological reactor utilizing phenol as an inhibitory substrate

Transient experiments were conducted on a Pseudomomas utilizing phenol in a continuous culture by disturbing the influent substrate concentration and dilution rate. Two stable steady states existed for some ranges of the parameters. Highly damped oscillations were observed in approaching a new high conversion steady state or in returning to a new high conversion steady state following a small disturbance. When a large disturbance was applied there was a smooth (overdamped) approach to a new low conversion steady state. The observed oscillatory behavior for small disturbances was predicted by a modified Powell-Ierusalemskii bottleneck model, but could not be predicted by a Monod-Haldane model; neither model was accurate for predicting the effect of large disturbances. A constant wall growth factor was used to account for microbial film activity, and the existence of two stable states was directly due to the presence of the film.