Biodegradation of petroleum hydrocarbons based pollutants in contaminated soil by exogenous effective microorganisms and indigenous microbiome.

Microbial remediation is an eco-friendly and promising approach for the restoration of sites contaminated by petroleum hydrocarbons (PHCs). The degradation of total petroleum hydrocarbons (TPHs), semi volatile organic compounds (SVOCs) and volatile organic compounds (VOCs) of the soil samples collected from a petrochemical site by indigenous microbiome and exogenous microbes (Saccharomyces cerevisiae ATCC 204508/S288c, Candida utilis AS2.281, Rhodotorula benthica CBS9124, Lactobacillus plantarum S1L6, Bacillus thuringiensis GDMCC1.817) was evaluated. Community structure and function of soil microbiome and the mechanism involved in degradation were also revealed. After bioremediation for two weeks, the concentration of TPHs in soil samples was reduced from 17,800 to 13,100 mg/kg. The biodegradation efficiencies of naphthalene, benzo[a]anthracene, benzo[b]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, dibenzo[a,h]anthracene, 1,2,3-trichloropropane, 1,2-dichloropropane, ethylbenzene and benzene in soil samples with the addition of S. cerevisiae were 38.0%, 35.7%, 36.2%, 40.4%, 33.6%, 36.2%, 12.0%, 43.9%, 43.3% and 43.0%, respectively. The microbial diversity and community structure were improved during the biodegradation process. S. cerevisiae supplemented soil samples exhibited the highest relative abundance of the genus Acinetobacter for bacteria and Saccharomyces for yeast. The findings offer insight into the correlation between microbes and the degradation of PHC-based pollutants during the bioremediation process.

Biomineralization of Cd2+ and inhibition on rhizobacterial Cd mobilization function by Bacillus Cereus to improve safety of maize grains.

Reducing cadmium (Cd) bioavailability and rhizobacterial Cd mobilization functions in the rhizosphere via the inoculation of screened microbial inoculum is an environmental-friendly strategy to improve safety of crop grains. In this study, Bacillus Cereus, a model Cd resistant strain, was selected to explore its effects on Cd bioavailability and uptake, bacterial metabolic functions related to Cd mobilization. Results indicated that inoculation of Bacillus Cereus in maize roots of sand pot with water-soluble Cd (0.06-0.15 mg/kg) and soil pot with high Cd-contaminated soil (total Cd: 2.33 mg/kg; Cd extracted by NH4NO3: 38.6 µg/kg) could decrease water-soluble Cd ion concentration by 7.7-30.1% and Cd extracted with NH4NO3 solution by 7.8-22.5%, inducing Cd concentrations in maize grains reduced by 10.6-39.9% and 17.4-38.6%, respectively. Even for a single inoculation in soil, Cd concentration in maize grains still satisfy food safety requirements (Cd content: 0.1 mg/kg dry weight) due to its successful colonization on root surface of maize. Bacillus Cereus could enrich more plant growth promotion bacteria (PGPB) and down-regulate the expression of genes related to bacterial motility, membrane transports, carbon and nitrogen metabolism in the rhizosphere soil, decreasing Cd bioavailability in soil. Approximately 80% Cd2+ in media was transferred into intracellular, meanwhile Cd salts (sulfide and/or phosphate) were produced in Bacillus Cereus through biomineralization process. Overall, this study could provide a feasible method for improving safety of maize grains via the inoculation of Bacillus Cereus under Cd pollution.

Biological mechanisms of cadmium accumulation in edible Amaranth (Amaranthus mangostanus L.) cultivars promoted by salinity: A transcriptome analysis.

Strategies to prevent cadmium (Cd) mobilization by crops under salinity conditions differs among distinct genotypes, but the biological mechanisms of Cd accumulation in different genotype crops promoted by salinity have remained scarce. In this study, we investigated the biological mechanisms of Cd accumulation in two quite different amaranth cultivars of low-Cd accumulator Quanhong (QH) and high-Cd accumulator Liuye (LY) in response to salt stress. Transcriptomes analysis was carried out on leaves and roots tissues of LY and QH grown with exchangeable Cd 0.27 mg kg-1 and salinity 3.0 g kg-1 treatment or control conditions, respectively. A total of 3224 differentially expressed genes (DEGs) in LY (1119 in roots, 2105 in leaves) and 848 in QH (207 in roots, 641 in leaves) were identified. Almost in each fold change category (2-25, 25-210, >210), the numbers of DEGs induced by salinity in LY treatments were much more than those in QH treatments, indicating that LY is more salt sensitive. Gene ontology (GO) analysis revealed that salinity stress promoted soil acidification and Cd mobilization in LY treatments through the enhancive expression of genes related to adenine metabolism (84-fold enrichment) and proton pumping ATPase (50-fold enrichment) in roots, and carbohydrate hydrolysis (2.5-fold enrichment) in leaves compared with that of whole genome, respectively. The genes expression of organic acid transporter (ALMT) was promoted by 2.71- to 3.94-fold in roots, facilitating the secretion of organic acids. Salt stress also inhibited the expression of key enzymes related to cell wall biosynthesis in roots, reducing the physical barriers for Cd uptake. All these processes altered in LY were more substantially compared with that of QH, suggesting that salt sensitive cultivars might accumulate more Cd and pose a higher health risk.

Systematic stress adaptation of Bacillus subtilis to tetracycline exposure.

To alleviate the harmful effects of antibiotics on the environment and human health, the stress response and molecular network of Bacillus under tetracycline stress were investigated using a proteomics approach. During the exposure process, Bacillus subtilis exhibited a strong adaptation mechanism. Cell membrane and intracellular reactive oxygen species (ROS) level returned to normal after 5 h. A total of 312 upregulated and 65 downregulated proteins were identified, mainly involved in metabolism and the synthesis of ribosomes, DNA, and RNA. After tetracycline exposure, the core metabolism network was accelerated to supply precursors for the synthesis of DNA, RNA, proteins, peptidoglycans, and saturated fatty acids that were involved in ribosome protection, and strengthened the cell wall and cell membrane. The signal transduction pathways involved were analyzed in association with the stress response of B. subtilis at 15 min of exposure to tetracycline. The primary damage to the ribosome by tetracycline activated a series of response proteins. Antitoxin and heat-shock proteins were activated for the global regulation of transcription and metabolism. Trigger factor Tig was upregulated to ensure proper initiation of transcription and aerobic respiration. Temperature-sensor protein VicR from the two-component system was used by the cell to regulate the composition of the cell wall and cell membrane. The over-consumption of metabolites, such as phosphoribosyl diphosphate (PRPP), purine nucleoside triphosphate (GTP), and acetyl-CoA forced the cells to assimilate more sugar for glycolysis. To this end, methyl-accepting chemotaxis proteins (MCPs) and sugar transportation protein PtsG were upregulated, simultaneously. Ultimately, peroxidase was activated to eliminate the redundant ROS, to minimize cell damage. These findings presented a system-level understanding of adaption processes of bacteria to antibiotic stress.

Phosphate-solubilizing bacteria will not significantly remobilize soil cadmium remediated by weathered coal.

Cadmium (Cd) re-mobilize by phosphate-solubilizing bacteria (PSB) from immobilization contaminated soil has drawn great attention due to its serious threat to human health through food chain. However, Cd binding with weathered coal (WC), an effective Cd immobilization material, will be re-mobilized by PSB or not is still unclear. In this study, the soil and sand pots with Cd were respectively mixed with the weight fractions of 0‰, 2‰, and 3‰ WC, inoculated with or without PSB, and planted with Amaranthus mangostanus L. The experimental results indicated that: (i) Cd in soil was transformed into organic fraction with WC, which has been led to the Cd accumulation concentrations in roots and shoots reduced by 38.8% and 20.5%, respectively; (ii) PSB could promote the concentration of exchangeable-Cd fraction and soil Cd uptake by amaranth in all treatments; and (iii) WC application in sand pot respectively reduced the Cd accumulation by 47.5% in roots and 24.1% in shoots, but PSB inoculation showed no significant effect on Cd accumulation in plants under WC application. SEM, zeta potential, and FT-IR results showed that PSB inoculation after Cd immobilized by WC had no influence on the microstructure, amount of negative charge, type, and content of functional groups in WC, indicating that organic fraction Cd in WC was not re-mobilized by PSB. Therefore, the application of WC in contaminated soil was conducive to transforming Cd in organic-bound forms and intensifying Cd immobilization effects.

Benzo(a)pyrene degradation by cytochrome P450 hydroxylase and the functional metabolism network of Bacillus thuringiensis.

The relationship between benzo(a)pyrene biodegradation and certain target biomolecules has been investigated. To regulate the degradation process, the associated metabolism network must be clarified. To this end, benzo(a)pyrene degradation, carbon substrate metabolism and exometabolomic mechanism of Bacillus thuringiensis were analyzed. Benzo(a)pyrene was degraded through hydroxylation catalyzed by cytochrome P450 hydroxylase. After the treatment of 0.5 mg L-1 of benzo(a)pyrene by 0.2 g L-1 of cells for 9 d, biosorption and degradation efficiencies were measured at approximately 90% and 80%, respectively. During this process, phospholipid synthesis, glycogen, asparagine, arginine, itaconate and xylose metabolism were significantly downregulated, while glycolysis, pentose phosphate pathway, citrate cycle, amino sugar and nucleotide sugar metabolism were significantly upregulated. These findings offer insight into the biotransformation regulation of polycyclic aromatic hydrocarbons.

Low root/shoot (R/S) biomass ratio can be an indicator of low cadmium accumulation in the shoot of Chinese flowering cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee) cultivars.

Chinese flowering cabbage is a commonly consumed vegetable that accumulates Cd easily from Cd-contaminated soils. Cultivations of low-Cd cultivars are promising strategies for food safety, but low-Cd-accumulating mechanisms are not fully elucidated. To address this issue, 37 cultivars were screened to identify high- and low-Cd cultivars upon exposure to sewage-irrigated garden soil pretreated with different Cd concentrations (1.81, 2.90, and 3.70 mg kg-1dry soil). The results showed that shoot Cd concentrations differed among the cultivars by maximum degrees of 2.67-, 3.71-, and 3.00-fold under control and treatments, respectively. Soil-pot trial and hydroponic trial found no significant difference in Cd and Ca mobilization, uptake, and transport ability by root per weight between high- and low-Cd cultivars. Interestingly, a stable R/S ratio difference among cultivars (p < 0.01) was observed, and the cultivar variation of Cd accumulation in shoots was mainly dependent on their R/S ratios. R/S ratio was also statistically positively associated with Cd and Ca accumulation in high- and low-Cd cultivars (p < 0.05), both in soil and hydroponics culture. This was mainly due to the lower root biomass of low-Cd cultivars resulted in lower total release of root exudates, lower total Cd and Ca mobilization in rhizosphere soil, and lower total Cd and Ca uptake and transport. The higher shoot biomass of low-Cd cultivars also has dilution effects on Cd concentration in shoot. Overall, low R/S ratio may be regarded as a direct and efficient indicator of low Cd accumulation in the shoot of Chinese flowering cabbage. These findings provided the possibilities to screening low-Cd cultivars using their R/S ratio.

Exogenous Glycinebetaine Promotes Soil Cadmium Uptake by Edible Amaranth Grown during Subtropical Hot Season.

Exogenous glycinebetaine treatment is an effective measure for preventing crops from being exposed to drought and high temperature; however, the effects of this approach on the soil Cd uptake and accumulation by crops remain unclear. Pot experiments were conducted in this study to analyze the effect of glycinebetaine on the soil Cd uptake and accumulation by edible amaranth cultivated in Cd-contaminated soil. Results revealed that after exogenous glycinebetaine treatment on amaranth leaves during the vigorous growth period, the plant biomass, the Cd concentrations in the roots and shoots, and the Cd translocation factor (TF) were significantly higher than those of the control group. The highest Cd concentrations in the roots and shoots and the TF were higher by 91%, 96% and 23.8%, respectively, than the corresponding values in the control group. In addition, exogenous glycinebetaine treatment significantly increased leaf chlorophyll content and promoted the photosynthesis of edible amaranth. Consequently, the contents of soluble sugar, dissolved organic carbon, and low-molecular-weight organic acids significantly increased in the rhizosphere, resulting in Cd mobilization. Significant positive correlations were observed among the contents of leaf chlorophyll, Mg, Fe, pectin and Ca. Given that Cd shares absorption and translocation channels with these elements, we speculated that the increased leaf chlorophyll and pectin contents promoted the absorption and accumulation of Mg, Fe and Ca, which further promoted the absorption and translocation of Cd. These results indicated that exogenous glycinebetaine treatment during hot season would aggravate the health risks of crops grown in Cd-contaminated soils.

Effect of Phosphate-Solubilizing Bacteria on the Mobility of Insoluble Cadmium and Metabolic Analysis.

Phosphate-solubilizing bacteria (PSB) can promote plant growth by dissolving insoluble phosphate. Therefore, PSB may have the potential to improve the mobility of heavy metals in soils and enhance phytoextraction. This study isolated a few PSB strains that could dissolve CdCO3 and solid Cd in soil. Two typical PSB, namely, high- and low-Cd-mobilizing PSB (Pseudomonas fluorescens gim-3 and Bacillus cereus qh-35, respectively), were selected to analyze the metabolic profiles, metabolic pathways, and mechanisms of mobilization of insoluble Cd. A total of 34 metabolites secreted by the two PSB strains were identified. Gluconic acid was the main contributor to Cd dissolution (42.4%) in high-Cd-mobilizing PSB. By contrast, gluconic acid was not secreted in low-Cd-mobilizing PSB. Metabolic pathway analysis showed that gluconic acid was produced by the peripheral direct oxidation pathway. Hence, PSB with peripheral direct oxidation pathway were likely to have high-Cd-mobilizing capacity.

Cellular metabolism network of Bacillus thuringiensis related to erythromycin stress and degradation.

Erythromycin is one of the most widely used macrolide antibiotics. To present a system-level understanding of erythromycin stress and degradation, proteome, phospholipids and membrane potentials were investigated after the erythromycin degradation. Bacillus thuringiensis could effectively remove 77% and degrade 53% of 1 µM erythromycin within 24 h. The 36 up-regulated and 22 down-regulated proteins were mainly involved in spore germination, chaperone and nucleic acid binding. Up-regulated ribose-phosphate pyrophosphokinase and ribosomal proteins confirmed that the synthesis of protein, DNA and RNA were enhanced after the erythromycin degradation. The reaction network of glycolysis/gluconeogenesis was activated, whereas, the activity of spore germination was decreased. The increased synthesis of phospholipids, especially, palmitoleic acid and oleic acid, altered the membrane permeability for erythromycin transport. Ribose-phosphate pyrophosphokinase and palmitoleic acid could be biomarkers to reflect erythromycin exposure. Lipids, disease, pyruvate metabolism and citrate cycle in human cells could be the target pathways influenced by erythromycin. The findings presented novel insights to the interaction among erythromycin stress, protein interaction and metabolism network, and provided a useful protocol for investigating cellular metabolism responses under pollutant stress.

Response of edible amaranth cultivar to salt stress led to Cd mobilization in rhizosphere soil: A metabolomic analysis.

The present study aimed to investigate the metabolic response of edible amaranth cultivars to salt stress and the induced rhizosphere effects on Cd mobilization in soil. Two edible amaranth cultivars (Amaranthus mangostanus L.), Quanhong (low-Cd accumulator; LC) and Liuye (high-Cd accumulator; HC), were subject to salinity treatment in both soil and hydroponic cultures. The total amount of mobilized Cd in rhizosphere soil under salinity treatment increased by 2.78-fold in LC cultivar and 4.36-fold in HC cultivar compared with controls, with 51.2% in LC cultivar and 80.5% in HC cultivar being attributed to biological mobilization of salinity. Multivariate statistical analysis generated from metabolite profiles in both rhizosphere soil and root revealed clear discrimination between control and salt treated samples. Tricarboxylic acid cycle in root was up-regulated to cope with salinity treatment, which promoted release of organic acids from root. The increased accumulation of organic acids in rhizosphere under salt stress obviously promoted soil Cd mobility. These results suggested that salinity promoted release of organic acids from root and enhanced soil Cd mobilization and accumulation in edible amaranth cultivar in soil culture.

Impact of osmoregulation on the differences in Cd accumulation between two contrasting edible amaranth cultivars grown on Cd-polluted saline soils.

This study aimed to investigate the difference of osmoregulation between two edible amaranth cultivars, Liuye (high Cd accumulator) and Quanhong (low Cd accumulator), under salinity stress and determine the effects of such difference on Cd accumulation. A pot experiment was conducted to expose the plants to sewage-irrigated garden soil (mean 2.28 mg kg-1 Cd) pretreated at three salinity levels. Under salinity stress, the concentrations of Cd in the two cultivars were significantly elevated compared with those in the controls, and the Cd concentration in Liuye was statistically higher than that in Quanhong (p < 0.05). Salinity-induced osmoregulation triggered different biogeochemical processes involved in Cd mobilization in the rhizosphere soil, Cd absorption, and translocation by the two cultivars. Rhizosphere acidification induced by an imbalance of cation over anion uptake was more serious in Liuye than in Quanhong, which obviously increased soil Cd bioavailability. Salinity-induced injuries in the cell wall pectin and membrane structure were worse in Liuye than in Quanhong, increasing the risk of Cd entering the protoplasts. The chelation of more cytoplasmic Cd2+ with Cl- ions in the roots of Liuye promoted Cd translocation into the shoots. Furthermore, the less organic solutes in the root sap of Liuye than in that of Quanhong also favored Cd translocation into the shoots. Hence, osmoregulation processes can be regarded as important factors in reducing Cd accumulation in crop cultivars grown on saline soils.

Use of low-calcium cultivars to reduce cadmium uptake and accumulation in edible amaranth (Amaranthus mangostanus L.).

This study aimed to investigate the mechanism of low Cd accumulation in crops using edible amaranth (Amaranthus mangostanus L.) as a model. Fifteen amaranth cultivars were grown in long-term contaminated soil, and the differences in soil Cd mobilization, root uptake, and root-shoot translocation between low- and high-Cd accumulating cultivars were examined. The transport pathways of Cd across the root were further identified in Hoagland nutrient solution using the Ca channel blocker La3+, the ATP inhibitor 2, 4-dinitrophenol (DNP), and a nutrition-deficient culture. Cd concentrations in amaranth cultivars varied about six-fold and showed an elevated trend as the concentration of Ca and Zn increased (p < 0.01), but did not exhibit any correlation with Mg and Fe. The concentrations of essential metals (Ca, Mg, Zn, and Fe) in the rhizosphere of low-Cd cultivars were significantly lower than those of high-Cd cultivars, and decreased with decreasing levels of soluble rhizosphere exudates. These findings indicated that low co-mobilization of Cd with essential metals mediated by root-induced exudates of low-Cd cultivars contributed to its low accumulation in amaranth. Uptake of Cd was inhibited along with Ca by La3+ and DNP, but was promoted by Ca or Fe deficiency treatment. Therefore, the Ca pathway is likely the mode of Cd entry into amaranth roots, although Zn and Fe transporters may also be involved. Low-Ca cultivars exhibited lower Cd uptake capability than high-Ca cultivars. The low translocation efficiency of Cd from root to shoot also contributed to its low content accumulation in edible parts of amaranth.

Leaching heavy metals from the surface soil of reclaimed tidal flat by alternating seawater inundation and air drying.

Leaching experiments were conducted in a greenhouse to simulate seawater leaching combined with alternating seawater inundation and air drying. We investigated the heavy metal release of soils caused by changes associated with seawater inundation/air drying cycles in the reclaimed soils. After the treatment, the contents of all heavy metals (Cd, Pb, Cr, and Cu), except Zn, in surface soil significantly decreased (P < 0.05), with removal rates ranging from 10% to 51%. The amounts of the exchangeable, carbonate, reducible, and oxidizable fractions also significantly decreased (P < 0.05). Moreover, prolonged seawater inundation enhanced the release of heavy metals. Measurement of diffusive gradients in thin films indicated that seawater inundation significantly increased the re-mobility of heavy metals. During seawater inundation, iron oxide reduction induced the release of heavy metals in the reducible fraction. Decomposition of organic matter, and complexation with dissolved organic carbon decreased the amount of heavy metals in the oxidizable fraction. Furthermore, complexation of chloride ions and competition of cations during seawater inundation and/or leaching decreased the levels of heavy metals in the exchangeable fraction. By contrast, air drying significantly enhanced the concentration of heavy metals in the exchangeable fraction. Therefore, the removal of heavy metals in the exchangeable fraction can be enhanced during subsequent leaching with seawater.

Use of flue gas desulfurization gypsum for leaching Cd and Pb in reclaimed tidal flat soil.

A soil column leaching experiment was conducted to eliminate heavy metals from reclaimed tidal flat soil. Flue gas desulfurization (FGD) gypsum was used for leaching. The highest removal rates of Cd and Pb in the upper soil layers (0-30 cm) were 52.7 and 30.5 %, respectively. Most of the exchangeable and carbonate-bound Cd and Pb were removed. The optimum FGD gypsum application rate was 7.05 kg·m(-2), and the optimum leaching water amount for the application was 217.74 L·m(-2). The application of FGD gypsum (two times) and the extension of the leaching interval time to 20 days increased the heavy metal removal rate in the upper soil layers. The heavy metals desorbed from the upper soil layers were re-adsorbed and fixed in the 30-70 cm soil layers.

Effects of freshwater leaching on potential bioavailability of heavy metals in tidal flat soils.

Leaching experiments were conducted to investigate the effects of desalination levels and sediment depths on potential bioavailability of heavy metal (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) in tidal flat soils. The data showed that both the desalination levels (p < 0.001) and soil depths (p < 0.001) had significant effects on the concentrations of acid-volatile sulfide (AVS). AVS concentrations generally exhibited increasing trends with an increase in depth and decreasing trends with enhanced desalination levels. The desalination levels had significant (p < 0.05) effects on the concentrations of simultaneously extracted metal (SEM; Cd, Cr, Cu, Fe, Mn, Pb, and Zn). Moreover, the concentrations of SEM (Cd, Cr, Cu, Fe, Mn, Pb, and Zn) generally tended to decrease with an increase in the desalination level. The desalination treatment significantly reduced the ratios of SEM/AVS compared with control. However, the ratios of SEM/AVS increased with enhanced desalination levels in treatments. Results reveal that low desalination treatment is better for reducing toxicity to benthic organisms than high desalination treatment. Since these reclaimed tidal flats with low desalinisation are suitable for saline water aquaculture, transforming the present land use of reclaimed tidal flats from fresh water aquaculture into saline water aquaculture may reduce health risk of heavy metals remained in sediments. These results will also contribute to our understanding of the dynamic behavior of heavy metals in the reclamation of tidal flats during leaching and the role of the ratio of SEM/AVS predictions on assessing the ecological risks of reclaimed tidal flats.

Sequential dynamic artificial neural network modeling of a full-scale coking wastewater treatment plant with fluidized bed reactors.

This study proposed a sequential modeling approach using an artificial neural network (ANN) to develop four independent models which were able to predict biotreatment effluent variables of a full-scale coking wastewater treatment plant (CWWTP). Suitable structure and transfer function of ANN were optimized by genetic algorithm. The sequential approach, which included two parts, an influent estimator and an effluent predictor, was used to develop dynamic models. The former parts of models estimated the variations of influent COD, volatile phenol, cyanide, and NH4 (+)-N. The later parts of models predicted effluent COD, volatile phenol, cyanide, and NH4 (+)-N using the estimated values and other parameters. The performance of these models was evaluated by statistical parameters (such as coefficient of determination (R (2) ), etc.). Obtained results indicated that the estimator developed dynamic models for influent COD (R (2) = 0.871), volatile phenol (R (2) = 0.904), cyanide (R (2) = 0.846), and NH4 (+)-N (R (2) = 0.777), while the predictor developed feasible models for effluent COD (R (2) = 0.852) and cyanide (R (2) = 0.844), with slightly worse models for effluent volatile phenol (R (2) = 0.752) and NH4 (+)-N (R (2) = 0.764). Thus, the proposed modeling processes can be used as a tool for the prediction of CWWTP performance.

Sodium chloride salinity reduces Cd uptake by edible amaranth (Amaranthus mangostanus L.) via competition for Ca channels.

Soil salinity is known to enhance cadmium (Cd) accumulation in crops. However, the mechanism by which this occurs independent of the surrounding soil remains unclear. In this study, root adsorption and uptake of salt cations and Cd by edible amaranth under NaCl salinity stress were investigated in hydroponic cultures with 0, 40, 80, 120, and 160mM of NaCl and 27nM Cd. The dominant Cd species in the nutrient solution changed from free Cd(2+) to Cd chlorocomplexes as NaCl salinity increased. High salinity significantly reduced K, Ca, and Cd root adsorption and K, Ca, Mg, and Cd uptake. High salinity decreased root adsorption of Cd by 43 and 58 percent and Cd uptake by 32 and 36 percent in salt-tolerant and salt-sensitive cultivars, respectively. Transformation of Cd from free ion to chlorocomplexes is unlikely to have significantly affected Cd uptake by the plant because of the very low Cd concentrations involved. Application of Ca ion channel blocker significantly reduced Na, K, Ca, Mg, and Cd uptake by the roots, while blocking K ion channels significantly reduced Na and K uptake but not Ca, Mg, and Cd uptake. These results suggest that Na was absorbed by the roots through both Ca and K ion channels, while Cd was absorbed by the roots mainly through Ca ion channels and not K ion channels. Salinity caused a greater degree of reduction in Cd adsorption and uptake in the salt-sensitive cultivar than in the salt-tolerant cultivar. Thus, competition between Na and Cd for Ca ion channels can reduce Cd uptake at very low Cd concentrations in the nutrient solution.

[Isolation of an effective benzo [a] pyrene degrading strain and its degradation characteristics].

A strain which could utilize BaP as a sole carbon and energy source and efficiently degrade benzo[a] pyrene (BaP) was isolated from the contaminated sediments of Guiyu, Guangdong province, China. The strain was identified as Brevibacillus brevis based on physiological and biochemical experiments together with 16S rRNA sequence analysis. The experimental results showed that the biodegradation rate of BaP by B. brevis in 7 days was 51.35%. The study also demonstrated that pH, temperature, bacterial dosage, initial concentration of BaP and processing time were important factors for BaP degradation. B. brevis could tolerate wide pH and temperature ranges, from 2 to 12 degrees C and 25 to 40 degrees C, respectively. The optimum condition for BaP degradation was pH 7 and 25 degrees C. With the increase of B. brevis inoculation amount, the degradation efficacy displayed an initial increasing trend and then came to a plateau. And the increase of BaP concentration led to the enhancement of BaP degradation. Addition of salicylic, succinate and phthalate showed no obvious positive effect on BaP biodegradation. After degradation of BaP, the surface of B. brevis was wrinkled, and became depressed and deformed over time.

[Biodegradation of decabromodiphenyl ether by intracellular enzyme obtained from Pseudomonas aeruginosa].

The degradation characteristics of decabromodiphenyl ether (BDE-209) by crude enzyme from Pseudomonas aeruginosa were investigated. The results revealed that the degradation efficiency of the intracellular enzyme excreted from this bacterial strain reached 69.22% after incubation with 1 mg x L(-1) BDE-209 for 12 h. Temperature, pH, enzyme concentration and BDE-209 concentration all influenced the ability of crude enzyme to degrade BDE-209. When the BDE-209 concentration was 1 mg x L(-1), the optimal condition for enzymatic degradation was temperature 30 degrees C and pH 7.5, and the degradation rate increased with increasing enzyme concentration. The degradation process of BDE-209 by intracellular enzyme of the strain conformed to the first-order kinetic model. The highest reaction rate was achieved when the initial concentration of BDE-209 was 1 mg x L(-1) and the half-life of this substrate was 6.9 h. In addition, the biodegradation of BDE-209 can be well described by enzymatic reaction of high concentration substrate inhibition, with a maximum substrate utilization rate of 0.133 mg x (L x h)(-1), a Michaelis-Menten constant of 0.642 mg x L(-1), and an inhibitory constant of 1.558 mg x L(-1), respectively.