Respiration and Growth of Shewanella decolorationis S12 with an Azo Compound as the Sole Electron Acceptor

The ability of Shewanella decolorationis S12 to obtain energy for growth by coupling the oxidation of various electron donors to dissimilatory azoreduction was investigated. This microorganism can reduce a variety of azo dyes by use of formate, lactate, pyruvate, or H₂ as the electron donor. Furthermore, strain S12 grew to a maximal density of 3.0 × 10⁷ cells per ml after compete reduction of 2.0 mM amaranth in a defined medium. This was accompanied by a stoichiometric consumption of 4.0 mM formate over time when amaranth and formate were supplied as the sole electron acceptor and donor, respectively, suggesting that microbial azoreduction is an electron transport process and that this electron transport can yield energy to support growth. Purified membranous, periplasmic, and cytoplasmic fractions from S12 were analyzed, but only the membranous fraction was capable of reducing azo dyes with formate, lactate, pyruvate, or H₂ as the electron donor. The presence of 5 μM Cu²⁺ ions, 200 μM dicumarol, 100 μM stigmatellin, and 100 μM metyrapone inhibited anaerobic azoreduction activity by both whole cells and the purified membrane fraction, showing that dehydrogenases, cytochromes, and menaquinone are essential electron transfer components for azoreduction. These results provide evidence that the microbial anaerobic azoreduction is linked to the electron transport chain and suggest that the dissimilatory azoreduction is a form of microbial anaerobic respiration. These findings not only expand the number of potential electron acceptors known for microbial energy conservation but also elucidate the mechanisms of microbial anaerobic azoreduction.     

Anaerobic growth and potential for amino acid production by nitrate respiration in <Emphasis Type="Italic">Corynebacterium glutamicum</Emphasis>

Oxygen limitation is a crucial problem in amino acid fermentation by Corynebacterium glutamicum. Toward this subject, our study was initiated by analysis of the oxygen-requiring properties of C. glutamicum, generally regarded as a strict aerobe. This organism formed colonies on agar plates up to relatively low oxygen concentrations (0.5% O₂), while no visible colonies were formed in the absence of O₂. However, in the presence of nitrate (), the organism exhibited limited growth anaerobically with production of nitrite (), indicating that C. glutamicum can use nitrate as a final electron acceptor. Assays of cell extracts from aerobic and hypoxic cultures yielded comparable nitrate reductase activities, irrespective of nitrate levels. Genome analysis revealed a narK2GHJI cluster potentially relevant to nitrate reductase and transport. Disruptions of narG and narJ abolished the nitrate-dependent anaerobic growth with the loss of nitrate reductase activity. Disruption of the putative nitrate/nitrite antiporter gene narK2 did not affect the enzyme activity but impaired the anaerobic growth. These indicate that this locus is responsible for nitrate respiration. Agar piece assays using l-lysine- and l-arginine-producing strains showed that production of both amino acids occurred anaerobically by nitrate respiration, indicating the potential of C. glutamicum for anaerobic amino acid production.     

Respiration and growth of Shewanella decolorationis S12 with an Azo compound as the sole electron acceptor

The ability of Shewanella decolorationis S12 to obtain energy for growth by coupling the oxidation of various electron donors to dissimilatory azoreduction was investigated. This microorganism can reduce a variety of azo dyes by use of formate, lactate, pyruvate, or H(2) as the electron donor. Furthermore, strain S12 grew to a maximal density of 3.0 x 10(7) cells per ml after compete reduction of 2.0 mM amaranth in a defined medium. This was accompanied by a stoichiometric consumption of 4.0 mM formate over time when amaranth and formate were supplied as the sole electron acceptor and donor, respectively, suggesting that microbial azoreduction is an electron transport process and that this electron transport can yield energy to support growth. Purified membranous, periplasmic, and cytoplasmic fractions from S12 were analyzed, but only the membranous fraction was capable of reducing azo dyes with formate, lactate, pyruvate, or H(2) as the electron donor. The presence of 5 microM Cu(2+) ions, 200 microM dicumarol, 100 microM stigmatellin, and 100 microM metyrapone inhibited anaerobic azoreduction activity by both whole cells and the purified membrane fraction, showing that dehydrogenases, cytochromes, and menaquinone are essential electron transfer components for azoreduction. These results provide evidence that the microbial anaerobic azoreduction is linked to the electron transport chain and suggest that the dissimilatory azoreduction is a form of microbial anaerobic respiration. These findings not only expand the number of potential electron acceptors known for microbial energy conservation but also elucidate the mechanisms of microbial anaerobic azoreduction.     

Concentration-Dependent Effects on Intracellular and Surface pH of Exposing <Emphasis Type="Italic">Xenopus</Emphasis> oocytes to Solutions Containing NH<Subscript>3</Subscript>/NH<Subscript>4</Subscript><Superscript>+</Superscript>

Others have shown that exposing oocytes to high levels of (10–20 mM) causes a paradoxical fall in intracellular pH (pH_i), whereas low levels (e.g., 0.5 mM) cause little pH_i change. Here we monitored pH_i and extracellular surface pH (pH_S) while exposing oocytes to 5 or 0.5 mM NH₃/NH₄ ⁺. We confirm that 5 mM causes a paradoxical pH_i fall (−ΔpH_i ≅ 0.2), but also observe an abrupt pH_S fall (−ΔpH_S ≅ 0.2)—indicative of NH₃ influx—followed by a slow decay. Reducing [NH₃/NH₄ ⁺] to 0.5 mM minimizes pH_i changes but maintains pH_S changes at a reduced magnitude. Expressing AmtB (bacterial Rh homologue) exaggerates −ΔpH_S at both levels. During removal of 0.5 or 5 mM NH₃/NH₄ ⁺, failure of pH_S to markedly overshoot bulk extracellular pH implies little NH₃ efflux and, thus, little free cytosolic NH₃/NH₄ ⁺. A new analysis of the effects of NH₃ vs. NH₄ ⁺ fluxes on pH_S and pH_i indicates that (a) NH₃ rather than NH₄ ⁺ fluxes dominate pH_i and pH_S changes and (b) oocytes dispose of most incoming NH₃. NMR studies of oocytes exposed to ¹⁵N-labeled show no significant formation of glutamine but substantial accumulation in what is likely an acid intracellular compartment. In conclusion, parallel measurements of pH_i and pH_S demonstrate that NH₃ flows across the plasma membrane and provide new insights into how a protein molecule in the plasma membrane—AmtB—enhances the flux of a gas across a biological membrane.

Effects of meal size,meal type,and body temperature on the specific dynamic action of anurans

Specific dynamic action (SDA), the increase in metabolism stemming from meal digestion and assimilation, varies as a function of meal size, meal type, and body temperature. To test predictions of these three determinants of SDA, we quantified and compared the SDA responses of nine species of anurans, Bombina orientalis, Bufo cognatus, Ceratophrys ornata, Dyscophus antongilli, Hyla cinerea, Kassina maculata, Kassina senegalensis, Pyxicephalus adspersus, and Rana catesbeiana subjected to meal size, meal type, and body temperature treatments. Over a three to seven-fold increase in meal size, anurans experienced predicted increases in postprandial rates of oxygen consumption the duration of elevated and SDA. Meal type had a significant influence on the SDA response, as the digestion and assimilation of hard-bodied, chitinous crickets, mealworms, and superworms required 76% more energy than the digestion and assimilation of soft-bodied earthworms, waxworms, and neonate rodents. Body temperature largely effected the shape of the postprandial metabolic profile; peak increased and the duration of the response decreased with an increase in body temperature. Variation in body temperature did not significantly alter SDA for four species, whereas both H. cinerea and R. catesbeiana experienced significant increases in SDA with body temperature. For 13 or 15 species of anurans ranging in mass from 2.4 to 270 g, SMR, postprandial peak and SDA scaled with body mass (log–log) with mass exponents of 0.79, 0.93, and 1.05, respectively.     

Pairwise NMR experiments for the determination of protein backbone dihedral angle Φ based on cross-correlated spin relaxation

Novel cross-correlated spin relaxation (CCR) experiments are described, which measure pairwise CCR rates for obtaining peptide dihedral angles Φ. The experiments utilize intra-HNCA type coherence transfer to refocus 2-bond coupling evolution and generate the or multiple quantum coherences which are required for measuring the desired CCR rates. The contribution from other coherences is also discussed and an appropriate setting of the evolution delays is presented. These CCR experiments were applied to ¹⁵N- and ¹³C-labeled human ubiquitin. The relevant CCR rates showed a high degree of correlation with the Φ angles observed in the X-ray structure. By utilizing these CCR experiments in combination with those previously established for obtaining dihedral angle Ψ, we can determine high resolution structures of peptides that bind weakly to large target molecules.     

Effects of common soil anions and pH on the uptake and accumulation of perchlorate in lettuce

A mechanistic understanding of perchlorate () entry into plants is important for establishing the human health risk associated with consumption of contaminated produce and for assessing the effectiveness of phytoremediation. To determine whether common soil anions affect uptake and accumulation in higher plants, a series of competition experiments using lettuce (Lactuca sativa L.) were conducted between (50 nM) and (4–12 mM), (1–10 mM), or Cl⁻ (5–15 mM) in hydroponic solution. The effects of (0–5 mM) and pH (5.5–7.5) on uptake were also examined. Increasing in solution significantly reduced the amount of taken up by green leaf, butter head, and crisphead lettuces. Sulfate and Cl⁻ had no significant effects on uptake in lettuce over the concentrations tested. Increasing pH significantly reduced the amount of taken up by crisphead and green leaf lettuces, whereas increasing significantly reduced uptake in butter head lettuce. The inhibition by across all lettuce genotypes suggests that may share an ion carrier with , and the decrease in uptake with increasing pH or provides macroscopic evidence for cotransport across the plasma membrane.     

Nitrogen metabolism of asparagine and glutamate in Vero cells studied by <Superscript>1</Superscript>H/<Superscript>15</Superscript>N NMR spectroscopy

Glutamine-free culture of Vero cells has previously been shown to cause higher cell yield and lower ammonia accumulation than that in glutamine-containing culture. Nitrogen metabolism of asparagine and glutamate as glutamine replacer was studied here using nuclear magnetic resonance (NMR) spectroscopy. ¹⁵N-labelled glutamate or asparagine was added and their incorporation into nitrogenous metabolites was monitored by heteronuclear multiple bond coherence (HMBC) NMR spectroscopy. In cells incubated with l-[¹⁵N]glutamate, the ¹⁵N label was subsequently found in a number of metabolites including alanine, aspartate, proline, and an unidentified compound. No detectable signal occurred, indicating that glutamate was utilized by transamination rather than by oxidative deamination. In cells incubated with l-[2-¹⁵N]asparagine, the ¹⁵N label was subsequently found in aspartate, the amine group of glutamate/glutamine, and in two unidentified compounds. Incubation of cells with l-[4-¹⁵N]asparagine showed that the amide nitrogen of asparagine was predominantly transferred to glutamine amide. There was no detectable production of , showing that most of the asparagine amide was transaminated by asparagine synthetase rather than deaminated by asparaginase. Comparing with a glutamine-containing culture, the activities of phosphate-activated glutaminase (PAG), glutamate dehydrogenase (GDH) and alanine aminotransferase (ALT) decreased significantly and the activity of aspartate aminotransferase (AST) decreased slightly.     

A Combined Patch-Clamp and Electrorotation Study of the Voltage- and Frequency-Dependent Membrane Capacitance Caused by Structurally Dissimilar Lipophilic Anions

Interactions of structurally dissimilar anionic compounds with the plasma membrane of HEK293 cells were analyzed by patch clamp and electrorotation. The combined approach provides complementary information on the lipophilicity, preferential affinity of the anions to the inner/outer membrane leaflet, adsorption depth and transmembrane mobility. The anionic species studied here included the well-known lipophilic anions dipicrylamine (DPA⁻), tetraphenylborate (TPB⁻) and [W₂(CO)₁₀(S₂CH)]⁻, the putative lipophilic anion and three new heterocyclic W(CO)₅ derivatives. All tested anions partitioned strongly into the cell membrane, as indicated by the capacitance increase in patch-clamped cells. The capacitance increment exhibited a bell-shaped dependence on membrane voltage. The midpoint potentials of the maximum capacitance increment were negative, indicating the exclusion of lipophilic anions from the outer membrane leaflet. The adsorption depth of the large organic anions DPA⁻, TPB⁻ and increased and that of W(CO)₅ derivatives decreased with increasing concentration of mobile charges. In agreement with the patch-clamp data, electrorotation of cells treated with DPA⁻ and W(CO)₅ derivatives revealed a large dispersion of membrane capacitance in the kilohertz to megahertz range due to the translocation of mobile charges. In contrast, in the presence of TPB⁻ and no mobile charges could be detected by electrorotation, despite their strong membrane adsorption. Our data suggest that the presence of oxygen atoms in the outer molecular shell is an important factor for the fast translocation ability of lipophilic anions.     

Cryogenic Synthesis of Molecules of Astrobiological Interest: Catalytic Role of Cosmic Dust Analogues

We have studied the effects of the substrate, namely amorphous olivine (MgFeSiO₄) cosmic dust analogues (CDAs), in synthesis of molecules obtained after 200 keV proton irradiation of formamide (NH₂COH). Formamide has been deposited on the olivine substrate at 20 K. The abundances of new molecular species formed after an irradiation dose of 12 eV/16 amu in formamide pure (i.e. deposited on an inert silicon substrate) and deposited on CDAs have been compared. Specifically, MgFeSiO₄ amorphous olivine is a selective catalyst preventing formation of NH₃ and CN⁻ molecules and changing the relative abundances of , CO₂, HNCO, CO. We have shown that the role of CDAs has to be taken into account in experiments simulating processes occurring in astronomical environments. Presented at: National Workshop on Astrobiology: Search for Life in the Solar System, Capri, Italy, 26 to 28 October, 2005.     

Nitrogen sink strength of ectomycorrhizal morphotypes of <Emphasis Type="Italic">Quercus douglasii</Emphasis>, <Emphasis Type="Italic">Q. garryana</Emphasis>, and <Emphasis Type="Italic">Q. agrifolia</Emphasis> seedlings grown in a northern California oak woodland

Little information is known on what the magnitude of nitrogen (N) processed by ectomycorrhizal (ECM) fungal species in the field. In a common garden experiment performed in a northern California oak woodland, we investigated transfer of nitrogen applied as ¹⁵NH₄ or ¹⁵NO₃ from leaves to ectomycorrhizal roots of three oak species, Quercus agrifolia, Q. douglasii, and Q. garryana. Oak seedlings formed five common ectomycorrhizal morphotypes on root tips. Mycorrhizal tips were more enriched in ¹⁵N than fine roots. N transfer was greater to the less common morphotypes than to the more common types. ¹⁵N transfer from leaves to roots was greater when , not , was supplied. ¹⁵N transfer to roots was greater in seedlings of Q. agrifolia than in Q. douglasii and Q. garryana. Differential N transfer to ectomycorrhizal root tips suggests that ectomycorrhizal morphotypes can influence flows of N from leaves to roots and that mycorrhizal diversity may influence the total N requirement of plants.     

Modification of the data-processing method for the turbidimetric bioassay of nisin

The data processing method of the turbidimetric bioassay of nisin was modified to facilitate its industrial application. The influence of the initial indicator concentration was minimized by a redefined specific dose of the bacteriocin as the quotient between the titer of the added bacteriocin and the initial population density of the indicator in the suspension. It was found that d _c = 0.125 μg ml⁻¹ was the critical dose of nisin that can cause a complete inhibition of the indicator, Pediococcus acidilactici UL5, with an initial OD of 0.135. To eliminate the interference of the cell debris, an equation, , exploiting d _c, was formulated to obtain the intrinsic survival proportion. The use of the specific dose of the bacteriocin and the intrinsic survival proportion as parameters of the dose/response curve greatly enhanced its repeatability and feasibility. A dual-dosage approach was developed to further simplify the conventional standard dose/response curve method.     

Cell-to-cell pathway dominates xylem-epidermis hydraulic connection in<Emphasis Type="Italic"> Tradescantia fluminensis</Emphasis> (Vell. Conc.) leaves

A steady supply of water is indispensable for leaves to fulfil their photosynthetic function. Understanding water movement in leaves, especially factors that regulate the movement of water flux from xylem to epidermis, requires that the nature of the transport pathway be elucidated. To determine the hydraulic linkage between xylem and epidermis, epidermal cell turgor pressure (P _t) in leaves of Tradescantia fluminensis was monitored using a cell pressure probe in response to a 0.2 MPa step change in xylem pressure applied at the leaf petiole. Halftime of P _t changes were 10–30 times greater than that of water exchange across an individual cell membrane suggesting that cell-to-cell water transport constitutes a significant part of the leaf hydraulic path from xylem to epidermis. Furthermore, perfusion of H₂O₂ resulted in increases of both and by a factor of 2.5, indicating that aquaporins may play a role in the xylem to epidermis hydraulic link. The halftime for water exchange did not differ significantly between cells located at the leaf base (2.5 s), middle (2.6 s) and tip (2.5 s), indicating that epidermal cell hydraulic properties are similar along the length of the leaf. Following the pressure application to the xylem (0.2 MPa), P _t changed by 0.12, 0.06 and 0.04 MPa for epidermal cells at the base, middle and the tip of the leaf, respectively. This suggests that pressure dissipation between xylem and epidermis is significant, and that the pressure drop along the vein may be due to its structural similarities to a porous pipe, an idea which was further supported by measurements of xylem hydraulic resistance using a perfusion technique.     

Nitrate and phosphate removal by<Emphasis Type="Italic"> Spirulina platensis</Emphasis>

The cyanobacterium Spirulina platensis was used to verify the possibility of employing microalgal biomass to reduce the contents of nitrate and phosphate in wastewaters. Batch tests were carried out in 0.5 dm³ Erlenmeyer flasks under conditions of light limitation (40 mol quanta m^–2 s^–1) at a starting biomass level of 0.50 g/dm³ and varying temperature in the range 23–40°C. In this way, the best temperature for the growth of this microalga (30°C) was determined and the related thermodynamic parameters were estimated. All removed nitrate was used for biomass growth (biotic removal), whereas phosphate appeared to be removed mainly by chemical precipitation (abiotic removal). The best results in terms of specific and volumetric growth rates ( =0.044 day^–1, Q _x =33.2 mg dm^–3 day^–1) as well as volumetric rate and final yield of nitrogen removal ( =3.26 mg dm^–3 day^–1, =0.739) were obtained at 30°C, whereas phosphorus was more effectively removed at a lower temperature. In order to simulate full-scale studies, batch tests of nitrate and phosphate removal were also performed in 5.0 dm³ vessels (mini-ponds) at the optimum temperature (30°C) but increasing the photon fluence rate to 80 mol quanta m^–2 s^–1 and varying the initial biomass concentration from 0.25 to 0.86 g/dm³. These additional tests demonstrated that an increase in the inoculum level up to 0.75 g/dm³ enhanced both NO₃ ^– and PO₄ ^3– removal, confirming a strict dependence of these processes on biomass activity. In addition, the larger surface area of the ponds and the higher light intensity improved removal yields and kinetics compared to the flasks, particularly concerning phosphorus removal ( =0.032–0.050 day^–1, Q _x =34.7–42.4 mg dm^–3 day^–1, =3.24–4.06 mg dm^–3 day^–1, =0.750–0.879, =0.312–0.623 mg dm^–3 day^–1, and =0.224–0.440).     

Hydrochemical fluctuations and crustacean community composition in an ephemeral saline lake (Sua Pan,Makgadikgadi Botswana)

Fluctuating hydrochemistry, as a result of extreme hydrological regimes, imposes major physiological constraints on the biota of ephemeral saline lakes. While the inverse relationship between salinity and zooplankton species richness is well-known across salinity gradients, few studies have documented closely the response of zooplankton to seasonal changes in salinity. Weekly sampling during two flood seasons at Sua Pan, an intermittent saline lake in central Botswana demonstrated the importance of spatial and temporal salinity gradients for crustacean community composition, associated with a decline in species richness, from 11 to three species. Conductivity ranged between 320 and 125,800 μS cm⁻¹ during seasonal flooding; changing from dominance by and , Ca²⁺ and Mg²⁺, at the beginning of the floods, to NaCl dominated waters as the lake dried out and salinities increased. pH estimates generally ranged between 8.6 and 10, with maximum values recorded during initial flooding. Crustaceans comprised mainly Branchinella spinosa, Moina belli, Lovenula africana and Limnocythere tudoranceai, all of which occurred across a wide range of salinities, while halotolerant freshwater species (Metadiaptomus transvaalensis, Leptestheria striatochonca and the ostracods Plesiocypridopsis aldabrae, Cypridopsis newtoni and a newly identified Potamocypris species) disappeared above conductivities of 1,500 μS cm⁻¹. A unique crustacean composition in southern Africa was attributed to Sua Pans’ rare chemical composition among southern African saline lakes; flood waters on Sua Pan contained a higher proportion of Na⁺ and , and less K⁺, Mg²⁺ and than over 80% of records from salt pans elsewhere in southern African. The freshwater species of crustaceans in Sua Pan were similar to those found in other southern Africa lakes, and these similarities decreased in lakes with higher pH and proportions of Na, and less SO₄ and Mg in their chemical composition. The predominant saline tolerant species on Sua Pan, however, showed a greater similarity to those in saline lakes in southern and East Africa with higher proportions of and, particularly, Mg²⁺ in their chemical composition. Handling editor: J. M. Melack     

A new technique for continuous measurement of the heat of fermentation

Summary A special temperature control system has been developed and applied to continuous measuring of the heat evolved during a fermentation process. In this system, the fermentation broth was overcooled by a given constant cooling water flow. The excess heat removed from the fermentor was then made up by an immersion electrical heater. The action of the temperature controller was precisely monitored as it varied in response to the amount of heat produced by the microbial activities.The technique was used for determining the heat evolution byEscherichia coli grown on glucose. The ratio between quantities of total heat release and total oxygen consumption has been determined to be 0.556 MJ/mol O₂.The newly developed technique can be employed as an online sensor to monitor the microbial activities of either aerobic or anaerobic fermentation systems.Symbols C_c Heat capacity of cooling water (MJ/kg · °C) - C_p Heat capacity (MJ/kg · °C) - I Current of immersion heater (A) - K Constant in Equation (2) (h) - K Constant in Equation (13) (m³ · h · °C/MJ) - Q_c Flow rate of cooling water (m³/h) - Heat of agitation (MJ/m³ · h) - Heat dissipated by the bubbling gas (MJ/m³ · h) - Heat removal by the action of controller (MJ/m³ · h) - Heat of fermentation (MJ/m³ · h) - Heat loss to the surroundings (MJ/m³ · h) - Q_pass Constant average power dissipated by the immersion heater (MJ/m³ · h) - Fluctuating power dissipated by the immersion heater (MJ/m³ · h) - Power dissipated by the immersion heater (MJ/m³ · h) - T Temperature of fermentation broth (°C) - Constant average temperature of fermentation broth (°C) - Fluctuating temperature of fermentation broth (°C) - T_a Temperature of the ambient air (°C) - T_c Inlet temperature of cooling water (°C) - U₁A₁ Specific heat transfer coefficient for determination of heat loss to the surroundings (MJ/m³ · h · °C) - U₂A₂ Specific heat transfer coefficient for cooling surfaces (MJ/m³ · h · °C) - U₃A₃ Constant in Equation (16) (MJ/m³ · h · °C) - V Voltage of immersion heater (V) - V_L Liquid volume (m³) - OUR Oxygen uptake rate (mol O₂/m³ · h) Greek Letters H_fo The ratio between the total heat release and the total oxygen uptake (MJ/mol O₂) - _c Density of cooling water (kg/m³) - Time constant defined in Equation (6) (h) - _iM_iC_pi Heat capacity of system components (fermentation broth + fermentor jar + stainless steel) (MJ/m³ · °C)     

The humus layer determines SO<Subscript>4</Subscript><Superscript>2−</Superscript> isotope values in the mineral soil

Biocycling of sulfur (S) has been proposed to play an important role in the recovery of ecosystems following anthropogenic S deposition. Here, we investigated the importance of the humus layer in the biocycling of S in three forested catchments in the Gårdsjön area of southwestern Sweden with differing S inputs and S isotope signature values. These experimental sites consisted of two reference catchments and the Gårdsjön roof experiment catchment (G1), where anthropogenic deposition was intercepted from 1991 until May 2002 by a roof placed over the entire catchment area. Under the roof, controlled levels of deposition were applied, using a sprinkler system, and the only form of S added was marine SO₄²⁻ with a δ of +19.5‰.We installed ion exchange resin bags at the interface between the humus layer and mineral soil at each of the catchments to collect SO₄²⁻ passing through the humus. The resin bags were installed on four occasions, in 1999 and 2000, covering two summer and two winter periods. The ions collected by each bag during these sampling periods were then eluted and their δ values and SO₄²⁻ concentrations determined. The most striking result is that the average δ value in the resin bags was more than 12‰ lower compared to that of the sprinkler water in the G1 roof catchment. There was no increasing trend in the isotope value in the resin bag SO₄²⁻ despite that the roof treatment has been on-going for almost 10 years; the average value for all resin bags was +7.1‰. The highest δ values found in the G1 roof catchment were between +11‰ and +12‰. However, these values were all obtained from resin bags installed at a single sampling location. Throughfall and resin bag δ values were more similar in the two reference catchments: about +7.5‰ in both cases. There was, however, an increase in resin bag δ values during the first winter period, from about +7‰ to +9‰. The resin bag δ value was linearly and positively related (r² = 0.26, p < 0.001) to the amount of SO₄²⁻ extracted from the resin bags, if relatively high amounts (>50 mmol m⁻²) were excluded. High amounts of resin bag SO₄²⁻ seemed to be related to groundwater inputs, as indicated by the δ value. Our results suggest that rapid immobilization of SO₄²⁻ into a large organic S pool may alter the S isotope value and affect the δ values measured in the mineral soil and runoff.     

Probing the interactions of the solvated electron with DNA by molecular dynamics simulations: bromodeoxyuridine substituted DNA

Solvated electrons () are produced during water radiolysis and can interact with biological substrates, including DNA. To augment DNA damage, radiosensitizers such as bromo-deoxyuridine (BUdR), often referred to as an “electron affinic radiosensitizer”, are incorporated in place of isosteric thymidine. However, little is known about the primary interactions of with DNA. In the present study we addressed this problem by applying molecular modeling and molecular dynamics (MD) simulations to a system of normal (BUdR·A)-DNA and a hydrated electron, where the excess electron was modeled as a localized (H₂O)₆ anionic cluster. Our goals were to evaluate the suitability of the MD simulations for this application; to characterize the motion of around DNA (e.g., diffusion coefficients); to identify and describe configurational states of close localization to DNA; and to evaluate the structural dynamics of DNA in the presence of . The results indicate that has distinct space-preferences for forming close contacts with DNA and is more likely to interact directly with nucleotides other than BUdR. Several classes of DNA - contact sites, all within the major groove, were distinguished depending on the structure of the intermediate water layer H-bonding pattern (or its absence, i.e., a direct H-bonding of with DNA bases). Large-scale structural perturbations were identified during and after the approached the DNA from the major groove side, coupled with deeper penetration of sodium counterions in the minor groove. Figure A rare configuration showing direct interaction between the solvated electron and DNA, where (yellow) and N7(A16) are H-bonded. The close approach from the major groove side invokes deep Na⁺ (magenta) penetration into the minor DNA groove (Fig. 7a).     

Growth and laccase production kinetics of <Emphasis Type="Italic">Trametes versicolor</Emphasis> in a stirred tank reactor

White rot fungi are a promising option to treat recalcitrant organic molecules, such as lignin, polycyclic aromatic hydrocarbons, and textile dyes, because of the lignin-modifying enzymes (LMEs) they secrete. Because knowledge of the kinetic parameters is important to better design and operate bioreactors to cultivate these fungi for degradation and/or to produce LME(s), these parameters were determined using Trametes versicolor ATCC 20869 (ATCC, American Type Culture Collection) in a magnetic stir bar reactor. A complete set of kinetic data has not been previously published for this culture. Higher than previously reported growth rates with high laccase production of up to 1,385 U l⁻¹ occurred during growth without or glucose limitation. The maximum specific growth rate averaged 0.94 ± 0.23 day⁻¹, whereas the maximum specific substrate consumption rates for glucose and ammonium were 3.37 ± 1.16 and 0.15 ± 0.04 day⁻¹, respectively. The maximum specific oxygen consumption rate was 1.63 ± 0.36 day⁻¹.     

Anaerobic Ammonium Oxidation (Anammox) in Chesapeake Bay Sediments

Anaerobic ammonium oxidation (anammox) has recently been recognized as a pathway for the removal of fixed N from aquatic ecosystems. However, the quantitative significance of anammox in estuarine sediments is variable, and measurements have been limited to a few estuaries. We measured anammox and conventional denitrification activities in sediments along salinity gradients in the Chesapeake Bay and two of its sub-estuaries, the Choptank River and Patuxent River. Homogenized sediments were incubated with ^14/15N amendments of , , and to determine relative activities of anammox and denitrification. The percent of N₂ production due to anammox (ra%) ranged from 0 to 22% in the Chesapeake system, with the highest ra% in the freshwater portion of the main stem of upper Chesapeake Bay, where water column concentrations are consistently high. Intermediate levels of relative anammox (10%) were detected at locations corresponding to tidal freshwater and mesohaline locations in the Choptank River, whereas anammox was not detected in the tidal freshwater location in the Patuxent River. Anammox activity was also not detected in the seaward end of Chesapeake Bay, where water column concentrations are consistently low. The ra% did not correlate with accumulation rate in anoxic sediment incubations, but ra% was related to water column concentrations and salinity. Anammox bacterial communities were also examined by amplifying DNA extracted from the upper Chesapeake Bay sediment with polymerase chain reaction (PCR) primers that are specific for 16S rRNA genes of anammox organisms. A total of 35 anammox-like sequences were detected, and phylogenetic analysis grouped the sequences in two distinct clusters belonging to the Candidatus “Scalindua” genus.