Rheological properties of polysaccharides produced by a Zoogloea sp.

A newly isolated marine bacterium, identified as Zoogloea sp., produced two different polysaccharides: one was water-soluble and the other was cell-bound. Both had non-Newtonian, pseudoplastic fluid behaviour and the solutions had low activation energies. The solutions of these polysaccharides showed rheological behaviour over a wide range of pH (2–12) and temperature (20–80 °C), and compatibility with NaCl.     

Rheological properties of extracellular polysaccharide, Pestan, produced by Pestalotiopsis sp.

Summary The fluid behaviour of Pestan produced from Pestalotiopsis sp. KCTC 8637P was as a non-Newtonian fluid. The rheological behaviour of Pestan solution was examined by Power-law model, Herschel-Bulkley model and Arrhenius equation. As the result, Pestan solution was pseudoplastic behaviour with yield stress. According to increase of Pestan concentration, its flow index was decreased. Thus, low concentrations of Pestan solution were well exposed pseudoplastic property. Apparent viscosity of 0.2 % Pestan solution was 268.2 cP at 14.3 sec^–1 and was higher about 2.8 times than that of Xanthan gum solution. Apparent viscosity of Pestan solution was stable over a wide pH and was maximum at pH 8. Also, consistency index of Pestan solution was very stable over wide temperature than that of Xanthan gum solution.     

Effects of growth conditions on exopolysaccharide production by Cyanospira capsulata

Batch cultures of Cyanospira capsulata, a heterocystous cyanobacterium possessing a thick polysaccharidic capsule, were characterized by increasing viscosity owing to the continuous release of a soluble polysaccharide (EPS) into the culture medium. Both capsulated trichomes and solubilized EPS contributed to the flow properties of whole cultures. A typical pseudoplastic behaviour, the more marked the more aged were the cultures, was evidenced.The production of EPS was investigated under different growth conditions by changing some nutritional and physical parameters known to affect the synthesis of exopolysaccharides in algae and cyanobacteria. Among the factors tested (Ca²⁺, Mg²⁺ or PO₄⁻⁴ deficiencies, salinity and pH) only Mg²⁺ shortage caused a significant enhancement of the EPS production. Under continuous illumination in open ponds, the EPS productivity of batch cultures on standard mineral medium was about 5·8 g m⁻² day⁻¹, whereas under Mg²⁺ deficiency with a consequent increase of the cultures' viscosity     

Kinetics and physico-chemical characterization of exopolysaccharides produced by the cyanobacterium Oscillatoria formosa

Exopolysaccharides of the cyanobacterium Oscillatoria formosa have been physico-chemically characterized and kinetics of their production studied. The organism produced 334.8 μg EPS per ml culture in 24 days with the maximum rate of production obtained during initial days of growth. HPLC analysis of the EPS hydrolysate revealed that besides three unidentified sugars, EPS contained ribose, mannose, and galacturonic acid. FT-IR spectrum of EPS revealed the presence of methyl, carboxyl and C–N groups. Elemental analysis indicated the presence of 4.7% nitrogen in EPS. The organism produced 75.6% more EPS when incubated at 35°C compared to cultures at 28°C. Under varied nutritional conditions, though the growth of the organism was less yet it produced enhanced amounts of EPS. Aqueous dispersions of EPS showed non-Newtonian, pseudoplastic behaviour. The viscosity of the aqueous solution of EPS was quite stable over a wide range of pH and temperature but it was observed to be affected by CaCl_2.     

Production and partial characterization of a novel capsular polysaccharide KP-EPS produced by <Emphasis Type="Italic">Paenibacillus pabuli</Emphasis> strain ATSKP

The aerobic nitrogen fixing xylanolytic bacterium Paenibacillus pabuli strain ATSKP produces loosely attached capsular polysaccharide KP-EPS. On 0.5% birchwood xylan 70 ± 5.02 mg of KP-EPS was produced per gram dry weight of cells by the fourth day of growth in the absence of combined nitrogen source at 30°C. It was separated and purified using centrifugation, cold acetone precipitation and dialysis and is a sulfate containing heteropolymer as revealed by FT-IR spectrometry and elemental analysis. CHN analysis revealed the presence of 37.50% carbon, 5.90% hydrogen and 8.28% nitrogen in KP-EPS. Absence of phosphorus was confirmed by ³¹P NMR. ICP-OES analysis showed the presence of various metals in small concentrations. Specific binding with aniline blue suggested the presence of (1,3)-β-d-glucan. Thermal gravimetric analysis and differential scanning calorimetric analysis confirmed its thermal stability as high as 200°C. The EPS was not pseudo plastic and the viscosity was less than xanthan. The intrinsic viscosity did not reduce drastically when dissolved in 0.1 M NaCl.     

Sorption of Cu(II) and Cd(II) by extracellular polymeric substances (EPS) from Aspergillus fumigatus

Sorption of Cu(II) and Cd(II) onto the extracellular polymeric substances (EPS) produced by Aspergillus fumigatus was investigated for the initial pH of the solution, EPS concentrations, contact time, NaCl concentration, initial metal ion concentration and the presence of other ions in the solution. The results showed that the adsorption of metal ions was significantly affected by pH, EPS concentrations, initial metal concentration, NaCl concentration and co-ions. The sorption of Cu(II) and Cd(II) increased with increasing pH and initial metal ion concentration but decreased with an increase in the NaCl concentration. The maximum sorption capacities of A. fumigatus EPS calculated from the Langmuir model were 40 mg g⁻¹ EPS and 85.5 mg g⁻¹ EPS for Cu(II) and Cd(II), respectively. The binary metal sorption experiments showed a selective metal binding affinity in the order of Cu(II) > Pb(II) > Cd(II). Both the Freundlich and Langmuir adsorption models described the sorption of Cu(II) and Cd(II) by the EPS of A. fumigatus adequately. Fourier transform infrared spectroscopy (FTIR) analysis revealed that carboxyl, amide and hydroxyl functional groups were mainly correlated with the sorption of Cu(II) and Cd(II). Energy dispersive X-ray (EDX) system analysis revealed that the ion-exchange was an important mechanism involved in the Cu(II) and Cd(II) sorption process taking place on EPS.     

Evaluation of size exclusion chromatography (SEC) for the characterization of extracellular polymeric substances (EPS) in anaerobic granular sludges

The extracellular polymeric substances (EPS) extracted from three granular and one flocculant anaerobic sludges were characterised by size exclusion chromatography (SEC) using two serially linked chromatographic columns in order to obtain more detailed chromatograms. A Superdex peptide 10/300 GL (0.1–7 kDa) and Superdex 20010/300GL (10–600 kDa) from Amersham Biosciences were used in series with a mobile phase at pH 7 with an ionic strength of 0.223 M (phosphate buffer 50 mM and NaCl 150 mM). A part of the EPS molecules displays hydrophobic and/or ionic interactions with the column packing. Interactions could be modified by changing the mobile phase ionic strength or polarity (addition of acetonitrile). The detection wavelength (210 or 280 nm) affects strongly the EPS chromatogram. For a sludge originating from the same type of biofilms (i.e., anaerobic granules), the differences in EPS fingerprints are mainly due to differences in the absorbance of the chromatographic peaks, linked to EPS molecules content and composition. The EPS fingerprint changes significantly when the EPS originate from another type of anaerobic sludges. In addition, EPS fingerprints were affected by the extraction method used (centrifugation only; heat and centrifugation or cationic exchange resin and centrifugation). This phenomenon was observed mainly for the largest and smallest molecules and molecules which display interactions with column packing.     

Factors influencing seed germination of Salsola affinis (Chenopodiaceae), a dominant annual halophyte inhabiting the deserts of Xinjiang, China

Salsola affinis is a dominant annual inhabiting saline deserts of Xinjiang, China. Experiments were conducted to determine the effects of temperature, winged perianths and NaCl on seed germination and on germination recovery from the effects of saline conditions after transfer to distilled water. Freshly harvested seeds could germinate equally well in light and darkness at 5–30 °C. Attached winged perianths significantly inhibited germination, removal enhanced germination. However, germination was not inhibited in the presence of detached winged perianths in any of the temperature treatments. We suggest that the winged perianth is a mechanical barrier for radicle emergence, not a barrier for water uptake; hence, it inhibited germination. Germination of seeds from which the perianth had been removed was not affected by NaCl at concentrations below 0.4 mol/l, but it was significantly decreased by NaCl at concentrations of 0.6–2.0 mol/l. No seeds germinated at 4.0 mol/l NaCl. Seeds incubated in NaCl at concentrations of 0.05–4.0 mol/l for 14 days recovered after being transferred to distilled water. However, germination was lower than that in the non-saline control, indicating that a portion of the NaCl-treated seeds may lose their ability to germinate.     

Purification and characterization of two pepsins from the stomach of pectoral rattail (Coryphaenoides pectoralis)

Two pepsins (A and B) were purified from the stomach of pectoral rattail (Coryphaenoides pectoralis) by acidification, ammonium sulfate precipitation, gel filtration chromatography and anion exchange chromatography to obtain a single band on native-PAGE and SDS-PAGE. The purities of pepsin A and B were increased to 7.1- and 13.0-fold with approximately 5.7% and 2.2% yield, respectively. Pepsin A and B had the apparent molecular weights of 35 and 31 kDa, respectively, when analyzed using SDS-PAGE and Sephacryl S-200 gel filtration. Pepsin A and B showed maximal activity at pH 3.0 and 3.5, respectively, and had the same optimal temperature at 45 °C using hemoglobin as a substrate. Both pepsin A and B were stable in the pH range of 2.0–6.0 but were unstable at the temperatures greater than 40 °C. Activity of both pepsins was inhibited by pepstatin A and was activated by divalent cations, indicating pepsin characteristics. Activities of both pepsins continuously decreased as NaCl concentration increased (0–30%). The enzymes had high affinity and activity toward hemoglobin with K_m and K_cat values of 98–152 μM and 32–50 S^− 1, respectively. Purified pepsins generally showed the similar characteristics to other fish pepsins.     

The photosynthesis of Dunaliella parva Lerche as a function of temperature,light and salinity

The photosynthetic behaviour of Dunaliella parva Lerche from the athalassic lagoon of Fuente de Piedra (Málaga, Southern Spain) was studied experimentally at three NaCl concentrations (1, 2 and 3 M), five temperatures (15, 23, 31, 38 and 42°C) and nine different irradiances between 82 and 891 mol m^–2 s^–1. Results are analyzed to define the best growing conditions for the algae. D. parva shows the highest photosynthetic rates at a NaCl molarity of 2 M, under a moderate light intensity (600 mol m^–2 s^–1) at 31°C. Above this light intensity a clear photoinhibition of the photosynthesis was found at 2 M and 3 M of NaCl. D. parva is a halotolerant and a thermoresistant species as evidenced by its net photosynthesis rate and positive values of oxygen evolution at 42°C.Two methods for modelling photosynthesis vs. irradiance curves are discussed. The first is a single model, based on third-order polynomial equations, and the second is double model, based on hyperbolical Michaelis-Menten type functions and negative exponential to define photoinhibition.     

Biochemical characterisation of extracellular phytase (myo-inositol hexakisphosphate phosphohydrolase) from a hyper-producing strain of Aspergillus niger van Teighem

Aspergillus niger van Teighem, isolated in our laboratory from samples of rotten wood logs, produced extracellular phytase having a high specific activity of 22,592 units (mg protein)^–1 . The enzyme was purified to near homogeneity using ion-exchange and gel-filtration chromatography. The molecular properties of the purified enzyme suggested the native phytase to be oligomeric, with a molecular weight of 353 kDa, the monomer being 66 kDa. The purified enzyme exhibited maximum activity at pH 2.5 and 52–55°C. The enzyme retained 97% activity after a 24-h incubation at 55°C in the presence of 10 mM glycine, while 87% activity was retained when no thermoprotectant was added. Phytase activity was not affected by most metal ions, inhibitors and organic solvents. Non-ionic and cationic detergents (0.1–5%) stabilise the enzyme, while the anionic detergent (SDS), even at a 0.1% level, severely inhibited enzyme activity. The chaotropic agents guanidinium hydrochloride, urea, and potassium iodide (0.5–8 M), significantly affected phytase activity. The maximum hydrolysis rate (V_max) and apparent Michaelis-Menten constant (K_m) were 1,074 IU/mL and 606 M, respectively, with a catalytic turnover number of 3×10⁵ s^–1 and catalytic efficiency of 3.69×10⁸ M^–1 s^–1.     

Antioxidative response of Lemna minor plants exposed to thallium(I)-acetate

The physiological effects of thallium(I)-acetate on the duckweed Lemna minor after 1-, 4-, 7- and 14-d exposure were analyzed. High bioaccumulation of Tl (221 mg kg⁻¹ dry wt at 2.0 μM Tl-acetate) caused an inhibition of plant growth. After 14-d exposure, 0.2, 0.5, 1.0 and 2.0 μM Tl-acetate reduced the frond-number growth rate by 21.1%, 39.4%, 66% and 83.1%, respectively. Tl-acetate also induced a modulation of the antioxidative response by depleting the ascorbate content and affecting the antioxidative enzymes activities. Superoxide dismutase showed a continuous increase of activity (31–67%) after Tl-acetate exposure. Other antioxidative enzymes displayed a biphasic response to both the concentration and the exposure period. Exposure up to 7 d decreased the catalase activity (up to 40%) in plants treated with higher Tl-acetate concentrations. In contrast, 14-d exposure increased the activity of the enzyme (≥90%). Short-term exposure increased ascorbate peroxidase activity (13–41%), except in plants exposed to the highest Tl-acetate concentration. However, 14-d exposure decreased the enzyme activity at all concentrations tested (38–60%). Although pyrogallol peroxidase activity increased (up to 26%) during 4-d exposure, longer exposures to the highest two concentrations decreased the activity of the enzyme (25–48%). In general, short-term exposure to Tl-acetate activated the antioxidant capacity, which resulted in recovery of the frond-number growth rates in Tl-treated plants. In spite of the activation of the antioxidative response during short-term exposure, higher Tl-acetate concentrations increased the hydrogen peroxide level (up to 45%) and induced marked oxidative damage to lipids, proteins and DNA. Longer exposure induced a decline of the antioxidative response, and plants showed the symptoms of oxidative damage even at lower Tl-acetate concentrations. The genotoxic effect was evaluated by an alkaline version of the cellular and acellular Comet assay, which revealed an indirect genotoxic effect of Tl-acetate, suggesting oxidatively induced damage to DNA.     

Molecular cloning,expression, and biochemical characterization of a novel cold-active α-amylase from Bacillus sp. dsh19-1

A novel gene (ANK58566) encoding a cold-active α-amylase was cloned from marine bacterium Bacillus sp. dsh19-1 (CCTCC AB 2015426), and the protein was expressed in Escherichia coli. The gene had a length of 1302 bp and encoded an α-amylase of 433 amino acids with an estimated molecular mass of 50.1 kDa. The recombinant α-amylase (AmyD-1) showed maximum activity at 20 °C and pH 6.0, and retained about 35.7% of activity at 4 °C. The AmyD-1 activity was stimulated by Ca²⁺ and Na⁺. However, the chelating agent, EDTA, inactivated the enzyme. Moreover, AmyD-1 displayed extreme salt tolerance, with the highest activity in the presence of 2.0 M NaCl and 60.5% of activity in 5.0 M NaCl. The K_m, V_max and k_cat of AmyD-1 in 2.0 M NaCl were 2.8 mg ml⁻¹, 21.8 mg ml⁻¹ min⁻¹ and 933.5 s⁻¹, respectively, at 20 °C and pH 6.0 with soluble starch as substrate. MALDI-TOF MS (Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry) revealed that the end products of starch hydrolysis by AmyD-1 were glucose, maltose, maltotriose, maltotetraose, and malt oligosaccharides. Thus, AmyD-1 is one of the very few α-amylases that can tolerate low temperatures and high salt concentrations, which makes it to be a potential candidate for research in basic and applied microbiology.

     

Enzymatic preparation of wheat bran xylooligosaccharides and their stability during pasteurization and autoclave sterilization at low pH

Xylooligosaccharides (XOS) were prepared from wheat bran insoluble dietary fiber (WBIDF) by treatment with commercial xylanase preparation Sunzymes. XOS, with a purity of 95% (w/w) and degree of polymerization of 2-7 and the ratio of arabinose to xylose of 0.27, was obtained with a yield of approximately 31.2% of WBIDF. Their stability was evaluated by comparing with that of commercial fructooligosaccharides (FOS) during pasteurization (60–100 °C, 30 min) and autoclave sterilization (121 °C, 1 kg/cm², 10–50 min) at pH 2.0–4.0. XOS was characterized by a high thermal stability during pasteurization at pH 2.5–4.0 and sterilization at pH 3.0–4.0. Even at pH 2.0, the remaining XOS reached 97.2% (w/w) and 84.2% (w/w) during pasteurization (100 °C, 30 min) and sterilization (50 min), respectively. Compared with FOS, XOS was strongly resistant to lower acidic conditions. The results revealed that XOS was considered to be more suitable for use as functional food ingredients.     

Effect of Na+and K+Ions on the Luminescence of Intact Vibrio harveyiCells at Different pH Values

The bioluminescent activity of intact Vibrio harveyicells loaded with different concentrations of NaCl and KCl at different pH values was studied. In the pH range of 6.5–8.5, the effect of Na⁺was significantly higher than that of K⁺at all concentrations studied. Maximum luminescent activity was observed in cells loaded with 0.68 M NaCl. When Na⁺was nonuniformly distributed on the plasma membrane, the cell luminescence kinetics was nonstationary in the 20-min range: during incubation, the luminescence intensity increased at pH 6.5 and decreased at pH 8.5. The activation and damping rate constants depended on the Na⁺gradient value. The maximum of luminescent activity shifted during incubation from pH 8.5 to 6.5–7.0. The luminescence kinetics in the systems with KCl was stationary; the maximum level of luminescence was observed in the pH range of 7.0–7.5. Under Na⁺-controlled conditions, the cell respiration and luminescence changed in synchronism. The protonophore CCP at a concentration of 20 M completely inhibited luminescence at pH 6.5 and was ineffective at pH 8.5.     

Production of extracellular protease from halotolerant bacterium, Bacillus aquimaris strain VITP4 isolated from Kumta coast

A newly isolated halotolerant Bacillus sp. VITP4 was investigated for the production of extracellular protease. 16S rRNA gene analysis identified it as Bacillus aquimaris. Enzyme secretion corresponded with growth (G_t, 38 min) in the basal Zobell medium, reaching a maximum during stationary phase (630 U/ml, 48 h). Protease production was investigated in different salt concentrations (0–4 M). While growth was optimum in the basal medium, higher levels of protease activity were observed in 0.5 M salt medium (728 U/ml, 48 h) and 1 M salt medium (796 U/ml, 78 h) with 21% and 32% increase in production, respectively. Salt concentrations above 2.5 M did not support bacterial growth. The optimum pH and temperature for production were pH 7.5 and 37 °C, respectively. A combination of peptone and yeast extract yielded optimum protease secretion. Inorganic nitrogen sources proved to be less favourable. Production was reduced in the presence of readily available carbon sources owing to catabolic repression. Effect of various salts (1–6%) indicated favourable bacterial growth in these conditions for producing proteolytic molecules with increased activity. The study assumes significance in the ability of the halotolerant bacterium to survive in a wide range of salinity and yield optimum levels of extracellular protease.     

Supersaturation-limited and Unlimited Phase Transitions Compete to Produce the Pathway Complexity in Amyloid Fibrillation

Although amyloid fibrils and amorphous aggregates are two types of aggregates formed by denatured proteins, their relationship currently remains unclear. We used β₂-microglobulin (β2m), a protein responsible for dialysis-related amyloidosis, to clarify the mechanism by which proteins form either amyloid fibrils or amorphous aggregates. When ultrasonication was used to accelerate the spontaneous fibrillation of β2m at pH 2.0, the effects observed depended on ultrasonic power; although stronger ultrasonic power effectively accelerated fibrillation, excessively strong ultrasonic power decreased the amount of fibrils formed, as monitored by thioflavin T fluorescence. An analysis of the products formed indicated that excessively strong ultrasonic power generated fibrillar aggregates that retained β-structures but without high efficiency as seeds. On the other hand, when the spontaneous fibrillation of β2m was induced at higher concentrations of NaCl at pH 2.0 with stirring, amorphous aggregates became more dominant than amyloid fibrils. These apparent complexities in fibrillation were explained comprehensively by a competitive mechanism in which supersaturation-limited reactions competed with supersaturation-unlimited reactions. We link the kinetics of protein aggregation and a conformational phase diagram, in which supersaturation played important roles.     

Effect of sorbitol addition on the physicochemical characteristics of starch–fatty acid systems

Aqueous maize starch dispersions (20%) were heated at 100 °C, in the presence of myristic, palmitic or stearic acid potassium salts as well as of sorbitol added at concentrations up to 60% (dry starch). Flow behaviour measurements at 100 °C indicated that interactions took place between the starch–fatty acid systems and sorbitol resulting in viscosity increase which was more pronounced as the sorbitol content increased. Water solubility measurements showed that a major part of sorbitol was easily extracted by excess water whereas sorption experiments revealed that the moisture uptake rate was proportional to sorbitol content of the starch systems examined. Thermomechanical studies indicated that the starch–fatty acid samples containing sorbitol up to 40% exhibited antiplasticizing behaviour. Scanning electron microscopy studies revealed that at sorbitol concentrations over 30%, free sorbitol crystals were formed on the surface of starch–fatty acid samples, whereas the percentage crystallinity as well as the crystallite size of samples were proportional to sorbitol content.     

Bovine serum albumin partitioning in an aqueous two-phase system: Effect of pH and sodium chloride concentration

The partitioning of bovine serum albumin (BSA) in a polyethylene glycol 3350 (8% w/w)–dextran 37 500 (6% w/w)–0.05 M phosphate aqueous two-phase was investigated at different pHs, at varying concentrations of sodium chloride at 20°C. The effect of NaCl concentration on the partition coefficient of BSA was studied for the PEG–dx systems with initial pH values of 4.2, 5.0, 7.0, 9.0, and 9.8. The NaCl concentrations in the phase systems with constant pH value were 0.06, 0.1, 0.2, 0.3, and 0.34 M. It was observed that the BSA partition coefficient decreased at concentrations smaller than 0.2 M NaCl and increased at concentrations greater than 0.2 M NaCl for all systems with initial pHs of 4.2, 5.0, 7.0, 9.0, and 9.8. It was also seen that the partition coefficient of BSA decreased as the pH of the aqueous two-phase systems increased at any NaCl salt concentration studied.     

Properties and purification of the catalytic subunit of cyclic AMP-dependent protein kinase of adipose tissue

The catalytic subunit of cAMP-dependent protein kinase from rat adipose tissue was purified to apparent homogeneity by making use of the differential binding of the holoenzyme and the free catalytic subunit to CM-Sephadex and by gel chromatography. Stability and yield was improved by inclusion of nonionic detergent in all steps after dissociation of the holoenzyme. Isoelectric focusing separated enzyme species with pI values of 7.8 and 8.6–8.8. The amino acid composition was similar to the enzyme purified from other tissues. Enzyme activity was markedly unstable in dilute solutions (<5 μg/ml). Additions of nonionic detergent, glycerol, bovine serum albumin and, especially, histones stabilized the enzyme. With protamine, the catalytic subunit had an apparent K_m of 60 μM and V_max of 20 μmol·min⁻¹·mg⁻¹, corresponding values with mixed histones were 12 μM and 1.2 μmol·min⁻¹·mg⁻¹. With both protein substrates the apparent K_m for ATP was 11 μM. Concentrations of Mg²⁺ above 10 mM were inhibitory. Histone phosphorylation was inhibited by NaCl (50% at 0.5 M NaCl) while protamine phosphorylation was stimulated (4-fold at 1 M NaCl). Inorganic phosphate inhibited both substrates (histones: 50% at 0.3 M, and protamine: 50% at 0.5 M). pH optimum was around pH 9 with both substrates. The catalytic subunit contained 2.0 (range of three determinations, 1.7–2.3) mol phosphate/mol protein. It was autophosphorylated and incorporated ³²P_i from [γ-³²P]ATP in a time-dependent process, reaching saturation when approx. 0.1 mol phosphate/mol catalytic subunit was incorporated.