Simulation Model of the Coupling between Nitrification and Denitrification in a Freshwater Sediment

A model was constructed to simulate the results of experiments which investigated nitrification and denitrification in the freshwater sediment of Lake Vilhelmsborg, Denmark (K. Jensen, N. P. Sloth, N. Risgaard-Petersen, S. Rysgaard, and N. P. Revsbech, Appl. Environ. Microbiol. 60:2094-2100, 1994). The model output faithfully represented the profiles of O₂ and NO₃^- and rates of nitrification, denitrification, and O₂ consumption as the O₂ concentration in the overlying water was increased from 10 to 600 μM. The model also accurately predicted the response, to increasing O₂ concentrations, of the integrated (micromoles per square meter per hour) rates of nitrification and denitrification. The simulated rates of denitrification of NO₃^- diffusing from the overlying water (D_w) and of NO₃^- generated by nitrification within the sediment (D_n) corresponded to the experimental rates as the O₂ concentration in the overlying water was altered. The predicted D_w and D_n rates, as NO₃^- concentration in the overlying water was changed, closely resembled those determined experimentally. The model was composed of 41 layers 0.1 mm thick, of which 3 represented the diffusive boundary layer in the water. Large first-order rate constants for nitrification and denitrification were required to completely oxidize all NH₄⁺ diffusing from the lower sediment layers and to remove much of the NO₃^- produced. In addition to the flux of NH₄⁺ from below, the model required a flux of an electron donor, possibly methane. Close coupling between nitrification and denitrification, achieved by allowing denitrification to tolerate some O₂ (~10 μM), was necessary to reproduce the real data. Spatial separation of the two processes (no toleration by denitrification of O₂) resulted in too high NO₃^- concentrations and too low rates of denitrification.     

Effect of dietary fiber on microbial activity and microbial gas production in various regions of the gastrointestinal tract of pigs.

The microbial activity, composition of the gas phase, and gas production rates in the gastrointestinal tract of pigs fed either a low- or a high-fiber diet were investigated. Dense populations of culturable anaerobic bacteria, high ATP concentrations, and high adenylate energy charges were found for the last third of the small intestine, indicating that substantial microbial activity takes place in that portion of the gut. The highest microbial activity (highest bacterium counts, highest ATP concentration, high adenylate energy charge, and low pH) was found in the cecum and proximal colon. Greater microbial activity was found in the stomach and all segments of the hindgut in the pigs fed the high-fiber diet than in the pigs fed the low-fiber diet. Considerable amounts of O2 were found in the stomach (around 5%), while the content of O2 in gas samples taken from all other parts of the gastrointestinal tract was < 1%. The highest concentrations and highest production rates for H2 were found in the last third of the small intestine. No methane could be detected in the stomach or the small intestine. The rate of production and concentration of methane in the cecum and the proximal colon were low, followed by a steady increase in the successive segments of the hindgut. A very good correlation between in vivo and in vitro measurements of methane production was found. The amount of CH4 produced by pigs fed the low-fiber diet was 1.4 liters/day per animal. Substantially larger amounts of CH4 were produced by pigs fed the high-fiber diet (12.5 liters/day)(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of 4.5S RNA depletion on Escherichia coli protein synthesis and secretion.

We examined the synthesis of individual proteins following depletion of 4.5S RNA by using a strain deficient in the induction of heat shock proteins. We found that initially the synthesis of all proteins was equally affected, and the peptide elongation rate was reduced by approximately 10%. For up to 1 generation time after the onset of inhibition of total protein synthesis, the processing of secreted proteins was unaffected. After further depletion of 4.5S RNA, accumulation of precursors of secreted proteins was observed under some growth conditions.     

Biogeochemical cycling of sulfur and iron in sediments of a south-east Asian mangrove,Phuket Island,Thailand

Benthic sulfate reduction and sediment pools of sulfur and iron were examined during January 1992 at 3 stations in the Ao Nam Bor mangrove, Phuket, Thailand. Patterns of sulfate reduction rates (0–53 cm) reflected differences in physical and biological conditions at the 3 stations, and highest rates were found at the vegetated site within the mangrove (Rhizophora apiculata) forest. Due to extended oxidation of mangrove sediments, a large portion of the added³⁵S-label was recovered in the chromium reducible pools (FeS₂ and S⁰) (41–91% of the reduced sulfur). Pyrite was the most important inorganic sulfur component, attaining pool sizes 50–100 times higher than acid volatile pools (FeS). HCl-extractable (0.5 M HCl) iron pools, including Fe(II)_HCl and Fe(III)_HCl, were generally low and Fe(III)_HCl was only present in the upper surface layers (0–5 cm). Maximum concentrations of dissolved Fe²⁺ (35–285 M) occurred just about the depth where dissolved H₂S accumulated. Furthermore Fe²⁺ and H₂S coexisted only where concentrations of both were low. There was an accumulation of organic sulfur in the deep sediment at 2 stations in the inner part of the mangrove. The reoxidation of reduced sulfides was rapid, and storage of sulfur was minor in the upper sediment layers, where factors like bioturbation, the presence of roots, or tidal mixing enhance oxidation processes.Author of correspondence.     

Neisseria gonorrhoeae possesses two nicotinamide adenine dinucleotide-independent lactate dehydrogenases

Abstract An important metabolic capability of Neisseria gonorrhoeae is the utilization of host-derived lactate. Two isoenzymes of the membrane-associated, pyridine dinucleotide-independent type of lactate dehydrogenase (iLDH) participate in lactate assimilation, but exhibit distinctive properties. Isoenzyme iLDH-I utilized lactate exclusively as substrate, exhibiting a preference for the D-isomer. In contrast, isoenzyme iLDH-II exhibited broad substrate specificity (lactate, phenyllactate, and 4-hydroxyphenyllactate), but was stereospecific for the L-isomers. These results explain the difficulty in isolating mutants unable to utilize lactate.     

Distribution of Feline Blood Types Detected in the Copenhagen Area of Denmark

The purpose of the present study was to make the first survey of the distribution of feline AB blood types in the Copenhagen area of Denmark. A total of 244 cats (139 purebred cats and 105 Domestic Shorthair cats) were tested. 93% of all tested cats had blood type A. Neither an AB nor an O type cat was detected and thus, the frequency of blood type B among all tested cats was 7%. Most type B cats were purebred cats (Birman, British Shorthair and Persian cats). No association between sex and blood type could be demonstrated among British Shorthair and Persian cats. Thus, the present study indicates that cats in Denmark predominantly have blood type A, and that blood type B cats are rare, except for certain breeds such as Birman and British Shorthair cats.     

The X-ray structure analysis of bis-2,2′,N,N′-bipyridyl ketone cobalt(III) nitrate dihydrate

An X-ray structural analysis of bis-2,2′,N,N′-bipyridyl ketone cobalt(III) nitrate dihydrate, CoC₂₂H₂₀N₄O₄⁺· NO₃⁻·2H₂O,M_r=559.38 g/mol, P , a=8.862(2), b=16.195(3), c=8.772(2) Å, α=103.54(2), β=95.74(3), γ=105.07°, V=1164.4(4) ų, Z=2, D_x=1.595 g/cm³, Mo Kα radiation (λ=0.71073 Å), μ=7.8 cm⁻¹ and R=0.079, revealed a Co(III) cation in a slightly distorted octahedral environment. The structure reveals that the ligand di-2-pyridyl ketone (dpk) has undergone a hydration reaction across the ketone double bond and one of the hydrate oxygen atoms coordinated to the metal forming a tridentate chelate. This new Co(dpk-hydrate)₂⁺ complex displays the least distorted geometry yet reported for either 1:1 or 1:2 (metal:ligand) complexes. A geometry optimization using the INDO model Hamiltonian as implemented in the program ZINDO was performed on the title complex with the Co³⁺ modeled as a singlet. The result of the computation corroborates the geometry of the title complex as that expected for Co³⁺.     

Is there a threshold size regulating seaward migration of brown trout and Atlantic salmon?

We investigated the influence of variation in body size and growth rate on age of smolting in Atlantic salmon and brown trout in four different Norwegian rivers. In Atlantic salmon smolt ages varied between 2 and 6 years, and in brown trout between 2 and 7 years. Smolt age was negatively correlated with parr growth, and positively correlated with smolt size. Age at smolting was more variable in the two northern than the two southern rivers. Smolt sizes and ages were also more variable in brown trout than in Atlantic salmon. Based on the observed variation in smolt size and age, we reject the hypothesis that a threshold size alone regulates age at smolting. Within populations smolt age depends on growth rate so that fast-growing parr smolted younger and smaller than slow-growing parr. We hypothesize that smolt size and age is a trade-off between expected benefits and costs imposed by differences in individual growth rate.     

Na+, K+, Cl− cotransport and its regulation in Ehrlich ascites Tumor cells. Ca2+/Calmodulin and protein kinase C dependent pathways

Summary Net Cl^– uptake as well as unidirectional³⁶Cl influx during regulatory volume increase (RVI) require external K⁺. Half-maximal rate of bumetanide-sensitive³⁶Cl uptake is attained at about 3.3mm external K⁺. The bumetanide-sensitive K⁺ influx found during RVI is strongly dependent on both Na⁺ and Cl^–. The bumetanide-sensitive unidirectional Na⁺ influx during RVI is dependent on K⁺ as well as on Cl^–. The cotransporter activated during RVI in Ehrlich cells, therefore, seems to transport Na⁺, K⁺ and Cl^–. In the presence of ouabain and Ba⁺ the stoichiometry of the bumetanide-sensitive net fluxes can be measured at 1.0 Na⁺, 0.8 K⁺, 2.0 Cl^– or approximately 1 : Na, 1 : K, 2 : Cl. Under these circumstances the K⁺ and Cl^– flux ratios (influx/efflux) for the bumetanide-sensitive component were estimated at 1.34 ±0.08 and 1.82 ± 0.15 which should be compared to the gradient for the Na⁺, K⁺, 2Cl^– cotransport system at 1.75 ± 0.24.Addition of sucrose to hypertonicity causes the Ehrlich cells to shrink with no signs of RVI, whereas shrinkage with hypertonic standard medium (all extracellular ion concentrations increased) results in a RVI response towards the original cell volume. Under both conditions a bumetanide-sensitive unidirectional K⁺ influx is activated. During hypotonic conditions a small bumetanide-sensitive K⁺ influx is observed, indicating that the cotransport system is already activated.The cotransport is activated 10–15 fold by bradykinin, an agonist which stimulates phospholipase C resulting in release of internal Ca²⁺ and activation of protein kinase C.The anti-calmodulin drug pimozide inhibits most of the bumetanide-sensitive K⁺ influx during RVI. The cotransporter can be activated by the phorbol ester TPA. These results indicate that the stimulation of the Na⁺, K⁺, Cl^– cotransport involves both Ca²⁺/calmodulin and protein kinase C.