Bioaccumulation of silver by a multispecies community of bacteria

A stable community of bacteria that had unusually high tolerance of soluble silver was isolated from soil by chemostat enrichment. The community consisted of three bacteria: Pseudomonas maltophilia, Staphylococcus aureus and a coryneform organism. The pseudomonas was primarly responsible for the silver resistance. The tolerance of high silver concentrations, up to 100 mM Ag⁺, was greatly reduced when the community was grown in the absence of silver. Pseudomonas maltophilia comprised approximately 50% by numbers of the community when grown in chemostats in the presence or absence of Ag⁺ but large fluctuations occurred in population sizes of the other two bacteria; the S. aureus population was small (less than 1%) in the presence of Ag⁺ but comparised a third of the total numbers when Ag⁺ was omitted from the medium. Silver-resistant respiration of the silveradapted community was significant even when it was confronted with high concentrations of Ag⁺. In contrast the respiration of the coryneform organism and particularly S. aureus was highly sensitive to silver. The inhibition constants for silver-sensitive respiration were 0.78 mM and 0.04 mM for silver acclimatized and nonacclimatized communities respectively.The community had great capacity for silver bioaccumulation. Maximum concentrations of over 300 mg silver per g dry weight of biomass were recorded at an accumulation rate of 21 mg Ag⁺ h^-1 (g biomass)^-1. The extent of silver removal from solution was a function of initial concentration of silver; at low external concentrations (ca. 1 mM) all the silver was rapidly removed from solution, at high concentrations (ca. 12 mM) 84% removal occurred in 15 h.     

Biosorption of Pb<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> by Non-Living Biomass of <Emphasis Type="Italic">Spirulina</Emphasis> sp.

Removal of heavy metals (Pb²⁺, Zn²⁺) from aqueous solution by dried biomass of Spirulina sp. was investigated. Spirulina rapidly adsorbed appreciable amount of lead and zinc from the aqueous solutions within 15 min of initial contact with the metal solution and exhibited high sequestration of lead and zinc at low equilibrium concentrations. The specific adsorption of both Pb²⁺ and Zn²⁺ increased at low concentration and decreased when biomass concentration exceeded 0.1 g l⁻¹. The binding of lead followed Freundlich model of kinetics where as zinc supported Langmuir isotherm for adsorption with their r ² values of 0.9659 and 0.8723 respectively. The adsorption was strongly pH dependent as the maximum lead biosorption occurred at pH 4 and 10 whereas Zn²⁺ adsorption was at pH 8 and 10.     

Methanosarcina as the dominant aceticlastic methanogens during mesophilic anaerobic digestion of putrescible waste

Taking into account isotope ¹³C value a mathematical model was developed to describe the dynamics of methanogenic population during mesophilic anaerobic digestion of putrescible solid waste and waste imitating Chinese municipal solid waste. Three groups of methanogens were considered in the model including unified hydrogenotrophic methanogens and two aceticlastic methanogens Methanosaeta sp. and Methanosarcina sp. It was assumed that Methanosaeta sp. and Methanosarcina sp. are inhibited by high volatile fatty acids concentration. The total organic and inorganic carbon concentrations, methane production, methane and carbon dioxide partial pressures as well as the isotope ¹³C incorporation in PSW and CMSW were used for the model calibration and validation. The model showed that in spite of the high initial biomass concentration of Methanosaeta sp. Methanosarcina sp. became the dominant aceticlastic methanogens in the system. This prediction was confirmed by FISH. It is concluded that Methanosarcina sp. forming multicellular aggregates may resist to inhibition by volatile fatty acids (VFAs) because a slow diffusion rate of the acids limits the VFA concentrations inside the Methanosarcina sp. aggregates.     

Responses of periphyton to changes in current velocity, suspended sediment and phosphorus concentration

SUMMARY.

• 1 Research was performed in laboratory streams to evaluate periphytic biomass accrual, export, and community composition over a range of limiting nutrient (phosphorus) concentrations with variable velocity, and suspended sediment addition, in comparison to constant velocity and no suspended sediment. In fixed-velocity treatments, velocity increase to 60 cm s^?1 significantly enhanced biomass accrual, but further increase resulted in substantial biomass reduction. Average biomass loss rates did not change significantly over a velocity range of 10–80 cm s^?1. Diatoms were favoured at relatively high velocities and low phosphorus concentrations, whereas the blue-green Phormidium tended to dominate at higher SRP concentrations and the green Mougeotia seemed to prefer lower velocities.
• 2 Sudden increases in velocity raised instantaneous loss rates by an order of magnitude or more, but these high rates persisted only briefly. As a result, marked biomass reductions were not apparent a day after the velocity change. Dominance change from filamentous green or blue-green to diatoms immediately after the increase was reversed within 2 days. Loss rate increases due to solids addition were much smaller than those accompanying velocity increase, but simultaneous velocity elevation and solids addition produced instantaneous loss rates approximately double those with velocity increase alone.
• 3 The experiments demonstrated that an elevation in velocity, above that to which algae were accustomed, led to increased loss rates and temporarily reduced biomass. However, recolonization and growth after biomass reduction were apparently rapid. Substantial export of periphyton following solids addition required erosion of the protective boundary layer accompanied by a velocity increase. These results arc applicable to understanding the response of lotic periphytic algae to elevated, turbid storm discharges and similar runoff or high-flow events.
• 4 Areal uptake rates of P by algae growing in the laboratory streams increased with soluble reactive phosphorus (SRP) concentration, up to approximately 15 μg I^?1 in overlying water. They also increased above 35 cm s ^?1. Overall, uptake rate seemed to vary inversely with biomass. The ralio of areal uptake rate/biomass was significantly less where mean biomass was 411±6 mg chl a m^?2 compared to 223±17 mg chl a m^?2.
• 5 The results suggested that although nutrient uptake is primarily a surface phenomenon, diffusion to interior cells can also determine the responses of attached communities. Both diffusion and uptake rate were stimulated by increasing nutrient concentration and velocity up to certain levels, but became limited by biofilm thickness and scouring.

     

Calcium alginate entrapment of the yeast Rhodosporidium toruloides for the kinetic resolution of 1,2-epoxyoctane

Resting cells of the yeast Rhodosporidium toruloides (UOFS Y-0471) were immobilised in calcium alginate beads for the enantioselective kinetic resolution of racemic-1,2-epoxyoctane. The initial activity exhibited by immobilised cells was almost 50% lower than that of the free counterpart but was extremely stable when compared to the free cells. The concentration of the immobilised biomass had no effect on apparent enzyme activity but did lead to a decrease in single cell activity. An increase in both the alginate and CaCl₂ concentrations used for bead preparation led to a decrease in enzyme stability. An increase in the alginate concentration led to an increase in bead diameter. The stoichiometric equation for cross-linking of alginate was only obeyed when CaCl₂ concentrations higher than 0.4 M were utilised for bead preparation.     

Improving Mathematical Model in Biodegradation of PAHs Contaminated Soil Using Gram-Positive Bacteria

In published literature there are limited studies on the estimation of kinetic parameters of polycyclic aromatic hydrocarbons (PAHs) in soil. In addition, neither the kinetic studies were performed with Gram-positive bacteria nor conducted under non-indigenous condition in order to understand their removal performance. Thus, a mathematical model describing biodegradation of phenanthrene-contaminated soil by Corynebacterium urealyticum, bacterium isolated from municipal sludge, was developed in this study. The model includes three kinetic parameters that were determined using TableCurve 2D software, namely qmax (maximum substrate utilization rate per unit mass of bacteria), X (biomass concentration) and Ks (substrate concentration at one half the maximum substrate utilization rate). These parameters were evaluated and verified in five different initial phenanthrene concentrations. Highest degradation rate was determined to be 79.24 mg kg^?1 day^?1 at 500 mg kg^?1 initial phenanthrene concentrations. This high concentration shows that bacteria perform better in contaminated sand compared to liquid media. High r² values, ranging from 0.92 to 0.99, were obtained excluding 1000 mg/kg phenanthrene. The kinetic parameters, i.e., qmax and Ks, increased with the phenanthrene concentration and thus suggest that bacteria degrade at a higher degradation rate. This model successfully described the biodegradation profiles observed at different initial phenanthrene concentrations. The established model can be used to simulate the duration of phenanthrene degradation using only the value of the initial PAHs concentration.     

Modeling the Biodegradation Kinetics of Perchlorate in the Presence of Oxygen and Nitrate as Competing Electron Acceptors

A mathematical model was developed to describe the biodegradation kinetics of perchlorate in the presence of nitrate and oxygen as competing electron acceptors. The rate of perchlorate degradation is described as a function of the electron donor (acetate) degradation rate, the concentration of the alternate electron acceptors, and rates of biomass growth and decay. The kinetics of biomass growth are described using a modified Monod model, and inhibition factors are incorporated to describe the influence of oxygen and nitrate on perchlorate degradation. In order to develop input parameters for the model, a series of batch biodegradation studies were performed using Azospira suillum JPLRND, a perchlorate-degrading strain isolated from groundwater. This strain is capable of utilizing oxygen, nitrate, or perchlorate as terminal electron acceptors. The maximum specific growth rate (μ_max) and half-saturation constant (K _S ^don) for the bacterium when utilizing either perchlorate or nitrate were similar; 0.16 per h and 158 mg acetate/L, respectively. However, these parameters were different when the strain was growing on oxygen. In this case, μ_max and K _S ^don were 0.22 per h and 119 mg acetate/L, respectively. The batch experiments also revealed that nitrate inhibits perchlorate biodegradation by this strain. This finding was incorporated into the model by applying an inhibition coefficient (K _i ^nit) value of 25 mg nitrate/L. Combined with appropriate groundwater transport models, this model can be used to predict perchlorate biodegradation during in situ remediation efforts.     

Disruption of a filamentous fungal organism (N. sitophila) using a bead mill of novel design II. Increased recovery of cellulases

A native strain of Neurospora sitophila was disrupted using enzymatic pretreatment combined with mechanical disruption in order to facilitate recovery of constitutive cellulases. Exceptional disruption (approaching 100%) was achieved when the enzymatic pretreatment protocol was used prior to mechanical disruption at a low rotor speed via a new bead mill (the Annu Mill). Further, increased recovery of cellulases (ca. two-fold increases in cellulase activity per unit biomass) appears attainable when this disruption protocol is employed. The enzyme preparation employed was Zymolyase, which lyses the walls of viable fungi. Combined disruption of the mycelial biomass appears to provide a secondary source of cellulases from Neurospora sitophila in addition to the extracellular primary source derived from the filtered (unprocessed) fermentation broth.Nomenclature CMCase carboxymethyl cellulase - FPase filter paper'ase - IU international unit (mol liberated hydrolysis product/min.) - N number of passes through the bead mill (–) - R total fraction of cells disrupted (–) - Ro fraction of cells disrupted after enzymatic pretreatment alone (–) - X cell concentration (dry weight) (gDW/L) Abbreviations DW dry weight     

Optimization of Chlorella biomass harvesting by flocculation and its potential for biofuel production

Optimization of microalgal biomass harvesting is essential to produce effective and optimum outcomes that can contribute towards a feasible and economical harvesting technique. Two Chlorella species were used, namely, C. vulgaris and C. sorokiniana UKM3. Two essential factors affecting microalgal biomass harvesting via flocculation, namely, the initial pH of the microalgal broth and flocculant (chitosan) concentration were studied. The optimization process was conducted by using a response surface methodology (RSM) based on the model of face-centered-central composite design (FC-CCD). The potential for biofuel application of the harvested biomass was evaluated based on the production of fatty acid methyl esters (FAMEs) by transesterification. The quadratic models obtained from the RSM significantly fitted the experiment data as the p-values were less than 0.05. The initial pH of the microalgal suspension was found to have a more significant effect on the flocculation process than flocculant concentration. For C. vulgaris, the highest flocculant efficiency of 98.7% was obtained at a chitosan concentration of 0.2 g L^?1 and an initial pH of 12.0, whereas for C. sorokiniana UKM3, at 0.15 g L^?1 of chitosan and initial pH of 12.0 produced the highest efficiency of 97.1%. The harvested biomass of both species exhibited a high content of palmitic acid (C16:0) with 29.74 wt% and 11.81 wt% of dry biomass for C. vulgaris and C. sorokiniana UKM3, respectively. This study showed that Chlorella species can be harvested efficiently using the flocculation process and manifested an excellent potential for biodiesel production where palmitic acid (C16:0) is one of the main compounds for high-acid oil-biodiesel.

     

A 2-year experimental study on nutrient and predator influences on food web constituents in a shallow lake of north-west Spain

1. A 2‐year study was carried out on the roles of nutrients and fish in determining the plankton communities of a shallow lake in north‐west Spain. Outcomes were different each year depending on the initial conditions, especially of macrophyte biomass. In 1998 estimated initial ‘per cent water volume inhabited’ (PVI) by submerged macrophytes was about 35%. Phytoplankton biomass estimated as chlorophyll a was strongly controlled by fish, whereas effects of nutrient enrichment were not significant. In 1999 estimated PVI was 80%, no fish effect was observed on phytoplankton biomass, but nutrients had significant effects. Water temperatures were higher in 1998 than in 1999. 2. In the 1998 experiment, cladoceran populations were controlled by fish and cyanobacteria were the dominant phytoplankton group. There were no differences between effects of low (4 g fresh mass m^?2) and high (20 g fresh mass m^?2) fish density on total zooplankton biomass, but zooplankton biomass was higher in the absence of fish. With the high plant density in 1999, fish failed to control any group of the zooplankton community. 3. Total biovolume of phytoplankton strongly decreased with increased nutrient concentrations in 1998, although chlorophyll a concentrations did not significantly change. At higher nutrient concentrations, flagellate algae became more abundant with likely growth rates that could have overcompensated cladoceran feeding rates. This change in phytoplankton community composition may have been because of increases in the DIN : SRP ratio. Both chlorophyll a concentration and total phytoplankton biovolume increased significantly with nutrients in the 1999 experiment. 4. A strong decline of submerged macrophytes was observed in both years as nutrients increased, resulting in shading by periphyton. This shading effect could account for the plant decline despite lower water turbidity at the very high nutrient levels in 1998.     

Effects of Initial Phosphorus Concentration and Light Intensity on Biomass Yield per Phosphorus and Lipid Accumulation of Scenedesmus sp. LX1

Phosphorus has been considered as one of the most important limiting resources of large-scale production of microalgal biofuel. The approaches to increase biomass yield per phosphorus, along with the lipid accumulation properties of Scenedesmus sp. LX1, were investigated in this study. It was found that practical biomass yield per phosphorous was reduced with the increase of initial phosphorus (P) concentration, but increased with light intensity. The highest biomass yield per P of 4,500 kg-biomass/kg-P was achieved at initial phosphorus concentration of 0.05 mg?·?L^?1 under the light intensity of 320 μmol photon?·?m^?2?·?s^?1. Furthermore, the lipid content per biomass and triacylglycerols (TAGs) content per lipid were found to be positively correlated to biomass yield per P. With the biomass yield increased from 2,800 kg-biomass/kg-P to 4,500 kg-biomass/kg-P, the lipid content per microalgal biomass and TAG content per lipid increased from 18.7 % to 35.0 % and from 69.5 % to 83.0 %. These results suggested a possible approach to achieve high biomass production and high lipid content simultaneously.     

Biomass relationship to growth and phosphate uptake ofPseudomonas fluorescens,Escherichia coli andAcinetobacter radioresistens in mixed liquor medium

The ability ofPseudomonas fluorescens, Escherichia coli andAcinetobacter radioresistenns to remove phosphate during growth was related to the initial biomass as well as to growth stages and bacterial species. Phosphate was removed by these bacteria under favourable conditions as well as under unfavourable conditions of growth. Experiments showed a relationship between a high initial cell density and phosphate uptake. More phosphate was released than removed when low initial cell densities (10²–10⁵ cells ml^–1) were used. At a high initial biomass concentration (10⁸ cells ml^–1), phosphate was removed during the lag phase and during logarthmic growth byP. fluorescens. Escherichia coli. at high initial biomass concentrations (10⁷ cells ml^–1), accumulated most of the phosphate during the first hour of the lag phase and/or during logarithmic growth and in some cases removed a small quantily of phosphate during the stationary growth phase.Acinetobacter radioresistens, at high initial cell densities (10⁶, 10⁷ cells ml^–1) removed most of phosphate during the first hour of the lag phase and some phosphate during the stationary growth phase.Pseudomonas fluorescens removed phosphate more thanA. radioresistens andE. coli with specific average ranges from 3.00–28.50 mg L^–1 compared to average ranges of 4.92–17.14 mg L^–1 forA. radioresistens and to average ranges of 0.50–8.50 mg L^–1 forE. coli.     

Kinetics of biodegradation of diethylketone by Arthrobacter viscosus

The performance of an Arthrobacter viscosus culture to remove diethylketone from aqueous solutions was evaluated. The effect of initial concentration of diethylketone on the growth of the bacteria was evaluated for the range of concentration between 0 and 4.8 g/l, aiming to evaluate a possible toxicological effect. The maximum specific growth rate achieved is 0.221 h⁻¹ at 1.6 g/l of initial diethylketone concentration, suggesting that for higher concentrations an inhibitory effect on the growth occurs. The removal percentages obtained were approximately 88%, for all the initial concentrations tested. The kinetic parameters were estimated using four growth kinetic models for biodegradation of organic compounds available in the literature. The experimental data found is well fitted by the Haldane model (R ² = 1) as compared to Monod model (R ² = 0.99), Powell (R ² = 0.82) and Loung model (R ² = 0.95). The biodegradation of diethylketone using concentrated biomass was studied for an initial diethylketone concentration ranging from 0.8–3.9 g/l in a batch with recirculation mode of operation. The biodegradation rate found followed the pseudo-second order kinetics and the resulting kinetic parameters are reported. The removal percentages obtained were approximately 100%, for all the initial concentrations tested, suggesting that the increment on the biomass concentration allows better results in terms of removal of diethylketone. This study showed that these bacteria are very effective for the removal of diethylketone from aqueous solutions.     

Effects of temperature and glycerol and methanol‐feeding profiles on the production of recombinant galactose oxidase in Pichia pastoris

Optimization of protein production from methanol‐induced Pichia pastoris cultures is necessary to ensure high productivity rates and high yields of recombinant proteins. We investigated the effects of temperature and different linear or exponential methanol‐feeding rates on the production of recombinant Fusarium graminearum galactose oxidase (EC 1.1.3.9) in a P. pastoris Mut⁺ strain, under regulation of the AOX1 promoter. We found that low exponential methanol feeding led to 1.5‐fold higher volumetric productivity compared to high exponential feeding rates. The duration of glycerol feeding did not affect the subsequent product yield, but longer glycerol feeding led to higher initial biomass concentration, which would reduce the oxygen demand and generate less heat during induction. A linear and a low exponential feeding profile led to productivities in the same range, but the latter was characterized by intense fluctuations in the titers of galactose oxidase and total protein. An exponential feeding profile that has been adapted to the apparent biomass concentration results in more stable cultures, but the concentration of recombinant protein is in the same range as when constant methanol feeding is employed. © 2014 The Authors Biotechnology Progress published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers Biotechnol. Prog., 30:728–735, 2014     

Optimization of adenosine 5′-triphosphate extraction for the measurement of␣acidogenic biomass utilizing whey wastewater

A set of experiments was carried out to maximize adenosine 5′-triphosphate (ATP) extraction efficiency from acidogenic culture using whey wastewater. ATP concentrations at different microbial concentrations increased linearly as microbial concentration decreased. More than 50% of ATP was extracted from the sample of 39 mg volatile suspended solids (VSS)/l compared to the sample of 2.8 g VSS/l. The ATP concentrations of the corresponding samples were 0.74±0.06 and 0.49±0.05 mg/l, respectively. For low VSS concentrations ranging from 39 to 92 mg/l, the extracted ATP concentration did not vary significantly at 0.73±0.01 mg ATP/l. Response surface methodology with a central composite in cube design for the experiments was used to locate the optimum for maximal ATP extraction with respect to boiling and bead beating treatments. The overall designed intervals were from 0 to 15 min and from 0 to 3 min for boiling and bead beating, respectively. The extracted ATP concentration ranged from 0.01 to 0.74 mg/l within the design boundary. The following is a partial cubic model where η is the concentration of ATP and x _k is the corresponding variable term (k=boiling time and bead beating time in order): η=0.629+0.035x ₁–0.818x ₂–0.002x ₁ x ₂–0.003x ₁ ² +0.254x ₂ ² +0.002x ₁ ² x ₂. This model successfully approximates the response of ATP concentration with respect to the boiling- and bead beating-time. The condition for maximal ATP extraction was 5.6 min boiling without bead beating. The maximal ATP concentration using the model was 0.74 mg/l, which was identical to the experimental value at optimum condition for ATP extraction.     

A novel polyculture growth model of native microalgal communities to estimate biomass productivity for biofuel production

Native polyculture microalgae is a promising scheme to produce microalgal biomass as biofuel feedstock in an open raceway pond. However, predicting biomass productivity of native polycultures microalgae is incredibly complicated. Therefore, developing polyculture growth model to forecast biomass yield is indispensable for commercial-scale production. This research aims to develop a polyculture growth model for native microalgal communities in the Minamisoma algae plant and to estimate biomass and biocrude oil productivity in a semicontinuous open raceway pond. The model was built based on monoculture growth of polyculture species and it is later formulated using species growth, polyculture factor (k_value), initial concentration, light intensity, and temperature. In order to calculate species growth, a simplified Monod model was applied. In the simulation, 115 samples of the 2014–2015 field dataset were used for model training, and 70 samples of the 2017 field dataset were used for model validation. The model simulation on biomass concentration showed that the polyculture growth model with k_value had a root-mean-square error of 0.12, whereas model validation provided a better result with a root-mean-square error of 0.08. Biomass productivity forecast showed maximum productivity of 18.87 g/m²/d in June with an annual average of 13.59 g/m²/d. Biocrude oil yield forecast indicated that hydrothermal liquefaction process was more suitable with a maximum productivity of 0.59 g/m²/d compared with solvent extraction which was only 0.19 g/m²/d. With satisfactory root-mean-square errors less than 0.3, this polyculture growth model can be applied to forecast the productivity of native microalgae.     

Investigation of biomass concentration,lipid production,and cellulose content in Chlorella vulgaris cultures using response surface methodology

The microalgae Chlorella vulgaris produce lipids that after extraction from cells can be converted into biodiesel. However, these lipids cannot be efficiently extracted from cells due to the presence of the microalgae cell wall, which acts as a barrier for lipid removal when traditional extraction methods are employed. Therefore, a microalgae system with high lipid productivity and thinner cell walls could be more suitable for lipid production from microalgae. This study addresses the effect of culture conditions, specifically carbon dioxide and sodium nitrate concentrations, on biomass concentration and the ratio of lipid productivity/cellulose content. Optimization of culture conditions was done by response surface methodology. The empirical model for biomass concentration (R² = 96.0%) led to a predicted maximum of 1123.2 mg dw L^?1 when carbon dioxide and sodium nitrate concentrations were 2.33% (v/v) and 5.77 mM, respectively. For lipid productivity/cellulose content ratio (R² = 95.2%) the maximum predicted value was 0.46 (mg lipid L^?1 day^?1)(mg cellulose mg biomass^?1)^?1 when carbon dioxide concentration was 4.02% (v/v) and sodium nitrate concentration was 3.21 mM. A common optimum point for both variables (biomass concentration and lipid productivity/cellulose content ratio) was also found, predicting a biomass concentration of 1119.7 mg dw L^?1 and lipid productivity/cellulose content ratio of 0.44 (mg lipid L^?1 day^?1)(mg cellulose mg biomass^?1)^?1 for culture conditions of 3.77% (v/v) carbon dioxide and 4.01 mM sodium nitrate. The models were experimentally validated and results supported their accuracy. This study shows that it is possible to improve lipid productivity/cellulose content by manipulation of culture conditions, which may be applicable to any scale of bioreactors. Biotechnol. Bioeng. 2013; 110: 2114–2122. © 2013 Wiley Periodicals, Inc.     

High ethanol productivities using small Ca-alginate beads of immobilized cells of Zymomonas mobilis

Summary Zymomonas mobilis cells were immobilized into small 1 mm diameter beads of Ca-alginate in order to minimize mass transfer limitations and maximize immobilized cell activity. A combination of small bead size with a high cell concentration of 58 g dry wt. cell per lit. bead volume resulted in high ethanol productivities using a newly designed packed bed bioreactor system. Steady-state dilution rates ranging from 0.4 h^-1 to 3.9 h^-1 were run resulting in a maximum productivity of 102 g ethanol/l/h for an inlet substrate concentration of 100 g glu/l and 87% conversion. The bioreactor was run continuously at a fixed dilution rate for 384 h and short intermittent treatment of the beads with CaCl₂ temporarily increased ethanol productivity to a maximum of 116 g ethanol/l/h.     

Effects of molecular association on structure and dynamics of a collagenous peptide

Peptide GVKGDKGNPGWPGAPY from the triple-helix domain of type IV collagen aggregates in solution at a critical aggregation concentration of 18 mM. This molecular self association process is investigated by ¹H- and ¹³C-nmr spectroscopy. As a function of increasing peptide concentration, selective ¹H resonances are cooperatively chemically shifted by up to 0.04 ppm to apparently saturable values at high concentration. Pulsed field gradient nmr was used to derive translation diffusion constants that, as the peptide concentration is increased, also cooperatively and monotonically decrease to an apparent limiting value. An average number of 6 monomer units per aggregate have been estimated from diffusion constant and ¹³C relaxation data. Comparative ¹H nuclear Overhauser effect spectroscopy (NOESY) spectra accumulated at high and low peptide concentrations suggest that average internuclear distances are decreased as a result of peptide association. ¹³C-nmr multiplet spin-lattice relaxation and ¹³C- {¹H} NOE effects on ¹³C-enriched glycine methylene positions in the peptide demonstrate that overall molecular tumbling and backbone internal motions are attenuated in the aggregate state. Lowering the solution pD from pD 6 to pD 2 disrupts the aggregate state, suggesting a role for electrostatic interactions in the association process. Based on thermodynamic considerations, hydrophobic interactions also probably act to stabilize the aggregate state. These data are discussed in terms of an nmr/NOE constrained computer-modeled structure of the peptide. © 1993 John Wiley & Sons, Inc.     

Production ecology of phyto- and zooplankton in a eutrophic pond dominated byChaoborus flavicans (Diptera: Chaobolidae)

Primary production of phytoplankton and secondary production of a daphnid and a chaoborid were studied in a small eutrophic pond. The gross primary production of phytoplankton was 290 gC m⁻² per 9 months during April–December. Regression analysis showed that the gross primary production was related to the incident solar radiation and the chlorophylla concentration and not to either total phosphorus or total inorganic nitrogen concentration. The mean chlorophylla concentration (14.2 mg m⁻³), however, was about half the expected value upon phosphorus loading of this pond. The mean zooplankton biomass was 1.60 g dry weight m⁻², of whichDaphnia rosea and cyclopoid copepods amounted to 0.69 g dry weight m⁻² and 0.61 g dry weight m⁻², respectively. The production ofD. rosea was high during May–July and October and the level for the whole 9 months was 22.6 g dry weight m⁻².Chaoborus flavicans produced 10 complete and one incomplete cohorts per year. Two consecutive cohorts overlapped during the growing season. The maximum density, the mean biomass, and the production were 19,100 m⁻², 0.81 g dry weight m⁻², and 11.7 g dry weight m⁻²yr⁻¹, respectively. As no fish was present in this pond, the emerging biomass amounted to 69% of larval production. The production ofC. flavicans larvae was high in comparison with zooplankton production during August–September, when the larvae possibly fed not only on zooplankton but also algae.