Evaluation of the association of mercury(II) with some dicysteinyl tripeptides

The present study was undertaken to gain insight into the associations of mercury(II) with dicysteinyl tripeptides in buffered media at pH 7.4. We investigated the effects of increasing the distance between cysteinyl residues on mercury(II) associations and complex formations. The peptide–mercury(II) formation constants and their associated thermodynamic parameters in 3-(N-morpholino)propanesulfonic acid (MOPS) buffered solutions were evaluated by isothermal titration calorimetry. Complexes formed in different relative ratios of mercury(II) to cysteinyl peptides in ammonium formate buffered solutions were characterized by LTQ Orbitrap mass spectrometry. The results from these studies show that n-alkyl dicysteinyl peptides (CP 1–4), and an aryl dicysteinyl peptide (CP 5) can serve as effective “double anchors” to accommodate the coordination sites of mercury(II) to form predominantly one-to-one Hg(peptide) complexes. The aryl dicysteinyl peptide (CP 5) also forms the two-to-two Hg₂(peptide)₂ complex. In the presence of excess peptide, Hg(peptide)₂ complexes are also detected. Notably, increasing the distance between the ligating groups or “anchor points” in CP 1–5 does not significantly affect their affinity for mercury(II). However, the enthalpy change (ΔH) values (ΔH₁ ∼ −91 kJ mol⁻¹ and ΔH₂ ∼ −66 kJ mol⁻¹) for complex formation between CP 4 and 5 with mercury(II) are about one and a half times larger than the related values for CP 1, 2 and 3 (ΔH₁ ∼ −66 kJ mol⁻¹ and ΔH₂ ∼ 46 kJ mol⁻¹). The corresponding entropy change (ΔS) values (ΔS₁ ∼ −129 J K⁻¹ mol⁻¹ and ΔS₂ ∼ −116 J K⁻¹ mol⁻¹) of the structurally larger dicysteinyl peptides CP 4 and 5 are less entropically favorable than for CP 1, 2 and 3 (ΔS₁ ∼ −48 J K⁻¹ mol⁻¹ and ΔS₂ ∼ −44 J K⁻¹ mol⁻¹). Generally, these associations result in a decrease in entropy, indicating that these peptide–mercury complexes potentially form highly ordered structures. The results from this study show that dicysteinyl tripeptides are effective in binding mercury(II) and they are promising motifs for the design of multi-cysteinyl peptides for binding more than one mercury(II) ion per peptide.     

A multi-tolerant low molecular weight mannanase from Bacillus sp. CSB39 and its compatibility as an industrial biocatalyst

Bacillus sp. CSB39, isolated from popular traditional Korean food (Kimchi), produced a low molecular weight, thermostable mannanase (MnCSB39); 571.14 U/mL using locust bean gum galactomannan as a major substrate. It was purified to homogeneity using a simple and effective two-step purification strategy, Sepharose CL-6B and DEAE Sepharose Fast Flow, which resulted in 25.47% yield and 19.32-fold purity. The surfactant-, NaCl-, urea-, and protease-tolerant monomeric protein had a mass of ∼30 kDa as analyzed by SDS-PAGE and galactomannan zymography. MnCSB39 was found to have optimal activity at pH 7.5 and temperature of 70 °C. The enzyme showed ˃55% activity at 5.0–15% (w/v) NaCl, and ˃93% of the initial activity after incubation at 37 °C for 60 min. Trypsin and proteinase K had no effect on MnCBS39. The enzyme showed ˃80% activity in up to 3 M urea. The N-terminal amino acid sequence, ALKGDGX, did not show identity with reported mannanases, which suggests the novelty of our enzyme. Activation energy for galactomannan hydrolysis was 26.85 kJmol⁻¹ with a K_cat of 142.58 × 10⁴ s⁻¹. MnCSB39 had K_m and V_max values of 0.082 mg/mL and 1099 ± 1.0 Umg⁻¹, respectively. Thermodynamic parameters such as ΔH, ΔG, ΔS, Q₁₀, ΔG_E-S, and ΔG_E-T supported the spontaneous formation of products and the high hydrolytic efficiency and feasibility of the enzymatic reaction, which strengthen its novelty. MnCSB39 activity was affected by metal ions, modulators, chelators, and detergents. Mannobiose was the principal end-product of hydrolysis. Bacillus subtilis CSB39 produced a maximum of 1524.44 U mannanase from solid state fermentation of 1 g wheat bran. MnCSB39 was simple to purify, was active at a wide pH and temperature range, multi-stress tolerant and catalyzes a thermodynamically possible reaction, characteristics that suggests its suitability for application as an industrial biocatalyst.     

Metabolic engineering of Saccharomyces cerevisiae for the biotechnological production of succinic acid

The production of bio-based succinic acid is receiving great attention, and several predominantly prokaryotic organisms have been evaluated for this purpose. In this study we report on the suitability of the highly acid- and osmotolerant yeast Saccharomyces cerevisiae as a succinic acid production host. We implemented a metabolic engineering strategy for the oxidative production of succinic acid in yeast by deletion of the genes SDH1, SDH2, IDH1 and IDP1. The engineered strains harbor a TCA cycle that is completely interrupted after the intermediates isocitrate and succinate. The strains show no serious growth constraints on glucose. In glucose-grown shake flask cultures, the quadruple deletion strain Δsdh1Δsdh2Δidh1Δidp1 produces succinic acid at a titer of 3.62 g L^?1 (factor 4.8 compared to wild-type) at a yield of 0.11 mol (mol glucose)^?1. Succinic acid is not accumulated intracellularly. This makes the yeast S. cerevisiae a suitable and promising candidate for the biotechnological production of succinic acid on an industrial scale.     

Continuous Acid Blue 45 decolorization by using a novel open fungal reactor system with ozone as the bactericide

To maintain long-term lignin-degrading enzyme production under non-sterile conditions was a key to the technical application of white rot fungi in wastewater treatment. In this work, a novel open fungal reactor system with ozone as the bactericide, and using immobilized Phanerochaete chrysosporium, was built and operated continuously to produce the manganese peroxidase and decolorize the Acid Blue 45. The results showed that an average of 84% Acid Blue 45 decolorization, the manganese peroxidase production with its activity ranging from 63 U L⁻¹ to 5 U L⁻¹, was achieved during about 25 days system continuous operation. The contaminating bacteria in the reactor can be controlled at a level of 4.65 × 10⁴ CFU ml⁻¹ that did not adversely affect the fungal activity. The result of this study provides a new practical way for future design and operation of white-rot fungi reactor under non-sterile conditions.     

High hydrostatic pressure increased stability and activity of immobilized lipase in hexane

Lipases are important to high value product synthesis, modification, and enhancement. However, they are often unstable above 40 °C. While most current applications of high hydrostatic pressure (HHP) are for inactivating deleterious enzymes, there is evidence that HHP can stabilize and increase activity of some enzymes. This study examines the apparent kinetics of immobilized lipase-catalyzed synthesis of isoamyl acetate at HHP in hexane. HHP reduced thermal inactivation of lipase by up to 152% after 4 h at 80 °C and 400 MPa when compared to incubations at low pressure. No significant differences were found in activation energy (E_a) at different pressures, irrespectively of the pressurization and heating sequence, and were between 35.7 ± 3.5 and 47.8 ± 8.2 kJ mol^?1, depending on the method. In all methods utilized, activity at 63.5 and 80 °C at 400 MPa was greater (from about 20 to 96% increase) than at low pressure. Activity increased by 110% at low pressure versus a 239% increase at 350 MPa when the temperature was increased from 40 to 80 °C. Increasing pressure up to 350 MPa increased lipase activity while pressures greater than 350 MPa maintained or decreased lipase activity. Activation volume (ΔV^≠) appeared negative between ambient pressure and 200 MPa in contrast to a positive ΔV^≠ between 300 and 600 MPa. Apparent ΔV^≠ was 14.3 ± 1.7 or 15.2 ± 2.2 cm³ mol^?1 at 40 or 80 °C, respectively, between 300 and 500 MPa.     

Magnetic properties of six-coordinated high-spin cobalt(II) complexes: Theoretical background and its application

In this contribution we study and analyse the influence of the different parameters involved in the magnetic susceptibility of six-coordinated high-spin Co(II) complexes. We propose an empirical expression to fit the magnetic susceptibility of polycrystalline samples of mononuclear Co(II) complexes with an axial distortion, the variable parameters being Δ (axial distortion), α (orbital reduction factor) and λ (spin–orbit coupling). This expression avoids solving the 12 × 12 matrix associated to the distortion of the ⁴T_1g term. In order to take into account the magnetic coupling (J) in the polynuclear Co(II) complexes, a perturbational approach is proposed to describe their magnetic susceptibility in the whole temperature range (2–300 K) as a function of J, Δ, α and λ. This approach is valid in the limit of the weak magnetic coupling as compared to the spin–orbit coupling, |J/λ| < 0.1. The model allows the treatment of each cobalt(II) ion in axial symmetry as an effective spin S_eff = 1/2. That causes a drastic reduction of the matrix size of the polynuclear compounds from 12ⁿ × 12ⁿ to 2ⁿ × 2ⁿ, n being the number of Co(II) ions in the complex. The main advantage of the model is to make possible the fit of the magnetic susceptibility data of those polynuclear Co(II) complexes whose high nuclearity involved intractable matrices.     

Effects of shade treatments on the photosynthetic capacity,chlorophyll fluorescence,and chlorophyll content of Tetrastigma hemsleyanum Diels et Gilg

Tetrastigma hemsleyanum Diels et Gilg was grown under full sunlight and moderate and high levels of shade for one month to evaluate its photosynthetic and chlorophyll fluorescence response to different light conditions. The results showed that T. hemsleyanum attained greatest leaf size and P_n when cultivated with 67% shade. Leaves of seedlings grown with 90% shade were the smallest. Leaf color of plants grown under full sunlight and 50% shade was yellowish-green. The P_n value increased rapidly as PPFD increased to 200 μmol m^?2 s^?1 and then increased slowly to a maximum, followed by a slow decrease as PPFD was increased to 1000 μmol m^?2 s^?1. P_n was highest for the 67% shade treatment and the LSP for this shade treatment was 600 μmol m^?2 s^?1. Full sunlight and 50% shade treatments resulted in significant reduction of ETR and qP and increased NPQ. Chl a, Chl b and total chlorophyll content increased and Chl a/b values decreased with increased shading. Results showed that light intensity greater than that of 50% shade depressed photosynthetic activity and T. hemsleyanum growth. Irradiance less than that of 75% shade limited carbon assimilation and led to decreased plant growth. Approximately 67% shade is suggested to be the optimum light irradiance condition for T. hemsleyanum cultivation.     

Selecting salt-tolerant clones and evaluating genetic variability to obtain parents of new diploid and tetraploid germplasm in rhodesgrass (Chloris gayana K.)

We evaluated survival percentage under salt stress in 46 diploid and tetraploid clones of rhodesgrass (Chloris gayana K.) with the aim of obtaining salt tolerant clones. Fifteen clones were selected at 600 mM NaCl under hydroponic conditions. Survival percentage of the selected clones ranged between 50–100% and 50–75% for diploid and tetraploid clones, respectively. Genetic diversity among the 15 salt-tolerant clones was assessed using amplified fragment length polymorphism (AFLP). All tetraploid clones showed genetic diversity, whereas the diploid group included some genetically related clones. Clones tolerant at 600 mM NaCl and showed genetic diversity are proposed as parents for new synthetic varieties of each rhodesgrass ploidy.     

Liquid state fermentation of apple pomace sludge for the production of ligninolytic enzymes and liberation of polyphenolic compounds

Ligninolytic enzyme production and polyphenolic compound extraction by liquid-state culture of Phanerochaete chrysosporium ATCC 24275 was investigated by employing apple pomace sludge and synthetic medium. Different physico-chemical and biological parameters namely viscosity, zeta potential and particle size, viability and enzyme production were investigated. The ligninolytic enzyme production was higher in apple pomace sludge (45 U/l of laccase, 220 U/l of MnP and 6.5 U/l of LiP) than in synthetic medium (17 U/l of laccase, 37 U/l of MnP and 6 U/l). These maximal activities were found during the stationary and decline phase. It was also found that enzyme production was strongly correlated with P. chrysoporium viability in both synthetic medium and apple pomace sludge. Moreover, physico-chemical parameters, such as particle size, zeta potential and viscosity were strongly correlated to the viability of P. chrysosporium and to the ligninolytic enzyme production. An increase in polyphenol content extracted by acetone (383–720 mg GAE/l) was observed during fermentation of apple pomace and it was found that the polyphenol content extracted by ethanol increased ～1.5 fold until 67 h of fermentation and later it decreased. It was found that antioxidant activity increased to 35% and eventually decreased based on the change in the polyphenol content.     

Synthesis,biological evaluation of novel 4,5-dihydro-2H-pyrazole 2-hydroxyphenyl derivatives as BRAF inhibitors

A series of novel 4,5-dihydropyrazole derivatives (3a–3t) containing hydroxyphenyl moiety as potential V600E mutant BRAF kinase (BRAF^V600E) inhibitors were designed and synthesized. Docking simulation was performed to insert compounds 3d (1-(5-(5-chloro-2-hydroxyphenyl)-3-(p-tolyl)-4,5-dihydro-1H-pyrazol-1-yl)ethanone) and 3m (1-(3-(4-chlorophenyl)-5-(3,5-dibromo-2-hydroxyphenyl)-4,5-dihydro-1H-pyrazol-1-yl)ethanone) into the crystal structure of BRAF^V600E to determine the probable binding model, respectively. Based on the preliminary results, compound 3d and 3m with potent inhibitory activity in tumor growth may be a potential anticancer agent. Results of the bioassays against BRAF^V600E, MCF-7 human breast cancer cell line and WM266.4 human melanoma cell line all showed several compounds had potent activities IC₅₀ value in low micromolar range, among them, compound 3d and compound 3m showed strong potent anticancer activity, which were proved by that 3d: IC₅₀ = 1.31 μM for MCF-7 and IC₅₀ = 0.45 μM for WM266.5, IC₅₀ = 0.22 μM for BRAF^V600E, 3m: IC₅₀ = 0.97 μM for MCF-7 and IC₅₀ = 0.72 μM for WM266.5, IC₅₀ = 0.46 μM for BRAF^V600E, which were comparable with the positive control Erlotinib.     

Low-mass molecular dynamics simulation for configurational sampling enhancement: More evidence and theoretical explanation

It has been reported recently that classical, isothermal–isobaric molecular dynamics (NTP MD) simulations at a time step of 1.00 fs of the standard-mass time (Δt=1.00 fs^smt) and a temperature of ≤340 K using uniformly reduced atomic masses by tenfold offers better configurational sampling than standard-mass NTP MD simulations at the same time step. However, it has long been reported that atomic masses can also be increased to improve configurational sampling because higher atomic masses permit the use of a longer time step. It is worth investigating whether standard-mass NTP MD simulations at Δt=2.00 or 3.16 fs^smt can offer better or comparable configurational sampling than low-mass NTP MD simulations at Δt=1.00 fs^smt. This article reports folding simulations of two β-hairpins showing that the configurational sampling efficiency of NTP MD simulations using atomic masses uniformly reduced by tenfold at Δt=1.00 fs^smt is statistically equivalent to and better than those using standard masses at Δt=3.16 and 2.00 fs^smt, respectively. The results confirm that, relative to those using standard masses at routine Δt=2.00 fs^smt, the low-mass NTP MD simulations at Δt=1.00 fs^smt are a simple and generic technique to enhance configurational sampling at temperatures of ≤340 K.     

Detection of nickel in maize roots: A novel nondestructive approach by reflectance spectroscopy and colorimetric models

In this paper, a novel method capable of assessing nickel (Ni) uptake in intact plant roots is proposed and validated. Dimethylglyoxime (DMG) was used to stain roots of seven-day-old maize (Zea mays L.) seedlings grown in solutions containing 0, 0.025, 0.1, 0.2, and 0.5 mM Ni²⁺. A nondestructive approach by using reflectance spectroscopy and CIE XYZ and CIE L*a*b* color systems was used to investigate their optical properties. The maximum intensity in reflectance spectra at 545 nm (A₅₄₅) was used to monitor the development of DMG–Ni complexes. The values of A₅₄₅ were polynomially related to the concentration of Ni²⁺ in the growing solution (R² = 0.98), and significant correlations were also observed between A₅₄₅ and the two indicators of phytotoxicity, namely, root growth inhibition (I) and variations in the shoot-to-root ratio (S/R). The variation of dominant wavelength (λ_d) and excitation purity (P_e) graphically derived from the x, y color gamut in the CIE XYZ system paralleled the two highest Ni concentrations. Most of the color parameters in the CIE L*a*b* system were closely related to both Ni²⁺ concentrations in plant growing medium and the values of (I) and (S/R) used here as markers of Ni toxicity. The revealed dependences confirm that the prelaminar method proposed here is capable of nondestructive estimating of Ni concentrations in intact root tissue. The values of A₅₄₅ in the reflectance spectra of stained roots and color parameters, namely, opponent redness–greenness (a^*), integral color difference (ΔE)^*, lightness color difference (ΔL)^*, and hue angle difference (ΔH)^*, showed the highest potential for diagnostic purposes.     

Growth performances and carcass traits of Ovin Martinik lambs fed various ratios of tropical forage to concentrate under intensive conditions

Studies were conducted to determine the effects of supplementation upon intake, growth and carcass traits of Ovin Martinik hair sheep. Forty lambs weighing 20 ± 3.7 kg live weight (LW) were reared after weaning in individual pens during a 4-month experimental study. Four supplement levels were compared (10 lambs per treatment): the L0 group received the basal diet (tropical forage 0.75 UFL and 73 PDIN g kg⁻¹ DM, INRA system) without concentrate, the L150, L300 and L600 groups were offered in addition 150, 300 and 600 g day⁻¹ of concentrate (1.15 UFL and 151 PDIN g kg⁻¹ DM), respectively. Intake (5 days a week) and growth patterns (every fortnight) were measured on the 40 lambs, while digestibility measurements (five times throughout the experimental period) were determined on half of the animals fitted with faecal bags and which were slaughtered according to the standard procedure at 33–35 kg live weight for assessment of carcass traits and meat quality.The total dry matter intake (DMI) and digestibility increased (P < 0.01) with the inclusion ratio of the concentrate in the diet: 82 g DM kg W^−0.75 vs. 97 g DM kg W^−0.75 and 65% vs. 73% between the two extreme groups, whereas forage DMI decreased and the forage substitution ratio was calculated to be 0.65. Growth and feed/gain ratios significantly (P < 0.01) improved among the groups L0, L150 and L300, from an average of 134–188 g day⁻¹ and 7.0–5.7, respectively. The differences observed between L300 and L600 were not significant. Carcass weight and dressing out percentages significantly (P < 0.01) increased with the addition of concentrate to the ration: from 13.1 to 15.6 kg and from 39 to 46%, from L0 to L600, respectively. Consequently, the weights of the different cuts of the carcass varied. There was a significant effect of the supplementation level on the accumulation of internal fat tissues: the kidney fat weight increased from 107 to 237 g from the L0 to the L600 groups. No significant effect was observed on the carcass quality scores, the ultimate pH and the colour parameters of the meat.By increasing the nutritional density of the diet, it was possible to obtain well-conformed and heavier carcasses, with no apparent detrimental effect on the quality. The optimal supplement supply with good quality grass would be 300 g day⁻¹ in our conditions.     

Heterologous production of a temperature and pH-stable laccase from Bacillus vallismortis fmb-103 in Escherichia coli and its application

To enhance laccase yield, the laccase gene from Bacillus vallismortis fmb-103 was cloned and heterologously expressed in Escherichia coli BL21 (DE3) cells. The auto-induction strategy was applied during fermentation, and the process was controlled, as follows: Cu²⁺ was added when the optical density at 600 nm (OD₆₀₀) was 0.3, the fermentation temperature was adjusted to 16 °C when the OD₆₀₀ was 0.9, and fermentation was stopped after 50 h. The yield of recombinant laccase was up to 3420 U/L, as assayed by 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid). Recombinant laccase was purified 4.47-fold by heating for 10 min at 70 °C and dialyzing against 50–60% ammonium sulfate, retained more than 50% activity after 10 h at 70 °C, and demonstrated broad pH stability. Malachite green was efficiently degraded by recombinant laccase, especially in combination with mediators. These results provided a basis for the future application of recombinant laccase to malachite green degradation.     

Myrothecium verrucaria strain X-16, a novel parasitic fungus to Meloidogyne hapla

Options for control of northern root-knot nematode (NRKN, Meloidogyne hapla) on vegetables are very limited currently. In this study, we characterized the parasitism of Myrothecium verrucaria strain X-16, a new nematophagous fungus, on NRKN at the stages of eggs, J2, and adult females and evaluated its biocontrol efficacy in the greenhouse. Strain X-16 produced conidia that geminated and invaded in 80 h after in contact with eggs, causing the shrinkage and depression of egg shell and blastocolysis of the embryo. The strain also attacked 2nd-stage juveniles by producing developing surface networks of hyphae on the nematode body wall. Strain X-16 attacked adult females by producing dense networks of hyphae on the nematode body wall in 120 h. Strain X-16 had lethal effects (22–71% mortality) against NRKN J2 at the concentration as low as 3.1 × 10⁷ conidia/ml and with the incubation treatment time as short as 24 h. The lethal effects linearly increased with the increase of conidial concentration, with the estimated LC₅₀ values as low as 1.0 × 10⁸ conidia/ml. Soil treatments with strain X-16 at 1%, 2% or 4% (wt/wt) induced significant reductions in J2 nematode counts in 100 g of dry soil, Pf/Pi ratios and root-know index in cucumber in the greenhouse evaluations. These studies are the first to demonstrate that M. verrucaria is able to parasitize NRKN and strain X-16 can be a potential biocontrol agent for management of NRKN.     

Population densities,group size and biomass of ungulates in a lowland tropical rainforest forest of the eastern Himalayas

Large ungulate population monitoring is a crucial wildlife management tool as ungulates help in structuring and maintaining the large carnivore populations. Reliable data on population status of major ungulate prey species are still non-existent for most of the protected areas in the Indian part of the eastern Himalayan biodiversity hotspot. Twenty transects were monitored over a period of three years (2009–2011) totaling 600 km with an average length of 2 km. The estimated mean density of ungulates was 17.5 km⁻² with overall density of 48.7 km⁻². The wild pig Sus scrofa had the highest density (6.7 ± 1.2 km⁻²) among all the prey species followed by barking deer Muntiacus muntjak (3.9 ± 0.6 km⁻²), sambar Rusa unicolor (3.8 ± 0.5) and gaur Bos gaurus (3.5 ± 0.9 km⁻²). The estimated total ungulate biomass density was 2182.56 kg km⁻². This prey biomass can support up to 7.2 tigers per 100 km⁻². However, with two other sympatric carnivores sharing the same resources, the actual tiger numbers that can be supported will be lower. The estimated minor prey species was 31 km⁻² significantly 30.6% crop damages were reported by wild pig (p = 0.01) and 35.4% was elephant (p = 0.004). This data on ungulate densities and biomass will be crucial for carnivore conservation in this understudied globally significant biodiversity hotspot.     

The effects of arsenic and induced-phytoextraction methods on photosynthesis in Pteris species with different arsenic-accumulating abilities

Arsenic (As) accumulation and photosynthesis occur simultaneously in plants under As exposure. We investigated the effects of As and induced-phytoextraction methods on photosynthesis in two As hyperaccumulators (Pteris vittata and Pteris cretica var. nervosa) and two non-hyperaccumulators (Pteris semipinnata and Pteris ensiformis) under soil culture conditions. Chlorophyll fluorescence parameters (the maximum [F_v/F_m] and actual quantum efficiency [F_PSII]) and the activities of three photosynthetic enzymes (ATPase, ribulose-1, 5-bisphosphate carboxylase [RuBPC] and glyceraldehyde-3-phosphate dehydrogenase [GAPDH]) were measured. Arsenic accumulation and photosynthetic behaviours in response to enhanced-phytoextraction methods (trans-1, 2-cyclobexylenedinitrilotetraacetic acid [CDTA] and phosphorous [P] addition and soil pH adjustment) of P. cretica and P. semipinnata were monitored and compared under conditions of 100 mg As kg⁻¹. Significant decreases in the F_v/F_m (19.9%) and F_PSII (36.1%) were observed in P. vittata when exposed to 100 mg As kg⁻¹ in comparison to the control (0 mg As kg⁻¹). Compared to the control (0 mg As kg⁻¹), the activities of GAPDH increased by 0.5% in P. cretica var. nervosa and decreased by only 8.3% in P. vittata even when both of them were treated with 200 mg As kg⁻¹, whereas a significant decrease, 56.1% and 51.7%, of this enzyme was observed in P. semipinnata and P. ensiformis, respectively, when exposed to 50 mg As kg⁻¹. Compared to the control (0 mg CDTA kg⁻¹ or 0 mg P kg⁻¹), the activities of ATPase increased by 53.7% and 82.7% in P. cretica when exposed to 0.5 g CDTA kg⁻¹ and 50 mg P kg⁻¹, respectively, and an increase of up to 175% was also observed in P. semipinnata when exposed to 600 mg P kg⁻¹. The activities of GAPDH increased by 68.9% and 90.7% in P. cretica when exposed to 2 g CDTA kg⁻¹ and 600 mg P kg⁻¹, respectively, but a decrease of up to 60% was observed in P. semipinnata when exposed to 2 g CDTA kg⁻¹. The uptake of As in P. semipinnata increased by 80.9% and 73.3% when 1 g CDTA kg⁻¹ and 600 mg P kg⁻¹ were added, respectively, compared to the control (0 g CDTA kg⁻¹ or 0 mg P kg⁻¹). It was concluded that GAPDH played an important role in the photosynthesis of As hyperaccumulators under As treatments.     

Hexavalent chromium removal from aqueous solution by adsorption on treated sawdust

The studies on adsorption of hexavalent chromium were conducted by varying various parameters such as contact time, pH, amount of adsorbent, concentration of adsorbate and temperature. The kinetics of adsorption of Cr(VI) ion followed pseudo second order. Langmuir adsorption isotherm was employed in order to evaluate the optimum adsorption capacity of the adsorbent. The adsorption capacity was found to be pH dependant. Sawdust was found to be very effective and reached equilibrium in 3 h (adsorbate concentration 30 mg l⁻¹). The rate constant has been calculated at 303, 308, 313 and 318 K and the activation energy (E_a) was calculated using the Arrhenius equation. Thermodynamic parameters such as standard Gibbs energy (ΔG°) and heat of adsorption (ΔH_r) were calculated. The ΔG° and ΔH_r values for Cr(VI) adsorption on the sawdust showed the process to be exothermic in nature. The percentage of adsorption increased with decrease in pH and showed maximum removal of Cr(VI) in the pH range 4.5–6.5 for an initial concentration of 5 mg l⁻¹.     

Distribution of anammox bacteria in domestic WWTPs and their enrichments evaluated by real-time quantitative PCR

Enrichment of anaerobic ammonium oxidation (anammox) bacteria using five activated sludges in three domestic wastewater treatment plants (WWTPs) were processed in a short term of 70 days and evaluated by real-time quantitative PCR (RTQ-PCR). Before the enrichment, building phylogenetic trees of Planctomycetes phylum in four reactors of sequencing batch reactor (SBR), anoxic and oxic reactors of anaerobic–anoxic–oxic (A2O) process, and rotating biological contactor (RBC) revealed six groups of distantly relative genera of Planctomyces, Pirellula, Gemmata, Isophaera, Candidatus and putative anammox bacteria. All clones of Candidatus sp. were affiliated with anammox bacteria and the majority of anammox clones were related to Planctomycete KSU-1 (AB057453). The discovery of anammox bacteria in raw activated sludges provided a partial rationale for the utilization of activated sludge as a seeding source of the anammox process. To verify the activity of anammox bacteria in the activated sludges, enrichment cultivations were conducted using SBRs. The enrichment of anammox bacteria resulted in the significant anammox activity of three samples. Quantification of 16S rRNA gene of anammox bacteria using RTQ-PCR showed the highest concentration of anammox bacteria of 2.48 ± 0.22 × 10⁹ copies of 16S rRNA gene/mg-volatile suspended solids (VSS), which was the same order of magnitude as that of the referential granular anammox sludge, 6.23 ± 0.59 × 10⁹ copies of 16S rRNA gene/mg-VSS, taken from an anammox upflow anaerobic sludge blanket (UASB) reactor. The doubling time of anammox bacteria enriched in this study was 1.18 days. The growth yield of anammox bacteria enriched in this study was 4.75 ± 0.57 × 10⁶ copies of 16S rRNA gene/mg of ammonium- and nitrite-nitrogen, which was similar to 4.50 ± 0.61 × 10⁶ copies of 16S rRNA gene/mg of ammonium- and nitrite-nitrogen for the referential anammox sludge. Substrate uptake rates of three successful enrichments at the end of the enrichment were comparable to those of granular and suspended anammox sludges. Rapid enrichment of anammox bacteria using activated sludge could offer an alternative method for obtaining a large volume of seeding anammox sludge.