A<i>β</i>-Like Peptide Displayed on Bacteriophage T7 Catalyzes Chromate and Uranyl Reduction

In order to discover genes capable of catalyzing the reductive immobilization of toxic chromate and uranyl ions, we have created a T7 bacteriophage library containing cDNA from environmental microbes (i.e., Geobacter sulfurreducens and Shewanella oneidensis MR-1) that are known to mediate the reduction of chromate and uranyl ions. After three rounds of screening, ten bacteriophage mutants were found to mediate the NADH-dependent reduction of chromate and uranyl ions whose cDNA encodes polypeptide chains ranging 14 to 73 amino acids in length. All identified sequences contain disordered structural motifs similar to the β-amyloid peptide (Aβ) known to promote aggregation and formation of high-affinity metal binding sites. Confirmation of this structural similarity involved phage display of the 42 amino-acid Aβ-peptides that have been found to catalyze the NADH-dependent reduction of both chromate and uranyl ions. Transmission electron microscopy (TEM) and X-ray absorption near edge structure (XANES) measurements confirm that reduced uranium is present on the surface of bacteriophage expressing the Aβ-peptide. The surface-displayed Aβ-like peptide on bacteriophage has the potential to couple naturally occurring electron transfer shuttles present in soils to promote economically viable remediation of contaminated sites containing toxic chromate and uranyl ions.

Effect of biochar application on rice,wheat,and corn seedlings in hydroponic culture

In recent years,biochar has attracted considerable attention for soil quality improvement and carbon sequestration due to its unique physicochemical properties.However,the mechanism by which biochar application negatively affects the growth of crop seedlings has not been fully investigated.In this study,a hydroponic experiment was conducted to evaluate the response of rice,wheat,and corn seedlings to biochar application(CK,0 g/L;BC1,0.5 g/L;and BC2,1.0 g/L).Compared with the CK treatment,the BC1 and BC2 treatments decreased the fresh shoot and root weights of rice and corn seedlings(P<0.05),but there was no significant effect on wheat seedlings(P>0.05).For the contents of nutrient elements in seedlings,both BC1 and BC2 treatments hindered the roots from absorbing Fe and Cu and increased the uptake of Ca and Mn.Compared with the CK treatment,the translocation factor(TF)values of Ca,Mn,and Zn were significantly decreased especially in rice seedlings(35.3%-36.8%,68.7%-76.5%,and 29.8%-22.0%,respectively)under the BC1 and BC2 treatments,while only Mn was significantly decreased in wheat and corn seedlings(P<0.05).Transmission electron microscope(TEM)analysis of root cross-sections showed that nano-sized biochar particles(10~23 nm)were found in the root cells under BC2 treatment conditions.Our findings reveal that a large amount of biochar application can reduce nutrient absorption and translocation,and hinder rice,wheat,and corn seedlings,particularly rice seedling,in hydroponic system.

Short-term biochar effect on soil physicochemical and microbiological properties of a degraded alpine grassland

Soil remediation is an important part of the restoration process of degraded terrestrial ecosystems.Due to its unique properties,biochar is being used widely as an effective soil modifier in agricultural systems,but research is still rare on biochar application in grassland ecosystems,especially in degraded alpine grasslands.In this study,we conducted a plot experiment to investigate the effect of biochar application on soil physicochemical properties and microorganisms at the 0–20 cm soil depth of a degraded alpine grassland in Qinghai-Tibet Plateau,China.The experiment consisted of four corn straw biochar application levels(0%,0.5%,1%and 2%,with the percentage representing the ratio of biochar weight to the dry weight of soil in the surface 20 cm soil layer).When the biochar addition increased from 0%to 2%,total nitrogen,total organic carbon and available phosphorus in the 0–10 cm soil layer increased by 41%,55%and 45%,respectively,in the second year after biochar addition.Meanwhile,soil electrical conductivity decreased,and soil water content increased.Total microbial,fungal and bacterial biomasses in the 0–10 cm soil layer increased from 9.15 to 12.68,0.91 to 1.34,and 3.85 to 4.55μg g^(-1),respectively.The relative biomasses of saprophytic fungi and methanotrophic bacteria decreased,while the relative biomasses of ectomycorrhizal fungi and arbuscular mycorrhizal fungi increased.These results indicate that biochar has a great potential in improving microbial activity and soil fertility in soil remediation of the degraded alpine grassland.

Simultaneous removal of Cd(II)and As(III)from co-contaminated aqueous solution byα-FeOOH modified biochar

A novelα-FeOOH modified wheat straw biochar(α-FeOOH@BC)was developed and the findings of the current study showed thatα-FeOOH@BC is an efficient material for the simultaneous removal of cations(Cd(II))and anions(As(III))from aqueous solutions.The SEM,FTIR,and XRD analysis proved thatα-FeOOH@BC was covered byα-FeOOH.In the single adsorption system,the maximum adsorption capacities ofα-FeOOH@BC for Cd(II)and As(III)were 62.9 and 78.3 mg/g,respectively.In the dual adsorption system,the maximum adsorption capacities ofα-FeOOH@BC for Cd(II)and As(III)dropped to 39.3 and 67.2 mg/g,respectively.The adsorption capacities of Cd(II)and As(III)byα-FeOOH@BC were much higher by BC andα-FeOOH both in single and dual adsorbate system.The adsorption results were well fitted by the Langmuir and pseudo-second-order kinetics models.The Cd(II)and As(III)co-adsorption onα-FeOOH@BC had a competitive effect,and the dominant adsorption mechanisms were co-precipitation and ion exchange.Our study showed thatα-FeOOH@BC could be an effective remediation material for Cd(II)and As(III)co-adsorption from aqueous environment.

Effects of low molecular weight organic acids on aggregation behavior of biochar colloids at acid and neutral conditions

Low molecular weight organic acids(LMWOAs),as active components in the rhizosphere carbon cycling,may influence the environmental behaviors of biochar colloids.This study selected the pine-wood and wheat-straw biochars(PB and WB)as two typical biochars.The effects of typical LMWOAs(oxalic acid,citric acid,and malic acid)on aggregation kinetics of PB and WB colloids were investigated under pH 4 and 6 conditions.Critical coagulation concentrations(CCCs)of both PB and WB colloids were decreased with the LMWOAs regardless of the types of biochar and the solution pH,and the most significant effect occurred in pH 4 due to more LMWOAs sorption on the biochar colloids.The different types of LMWOAs caused various CCCs changes.For example,the CCC values of PB colloids decreased from 75 mM to 56,52,and 47 mM in the pH 4 NaCl solutions when 1 mM oxalic acid,citric acid,and malic acid were present in the suspensions,respectively.The chemical structure(functional groups)and molecular weight of LMWOAs,solution pH,and the electrophoretic mobility(EPM)of biochar co-influence the interactions between biochar colloids and LMWOAs,thus affecting the stability of biochar colloids in the presence of LMWOAs.The presence of LMWOAs accelerated the aggregation of colloidal biochar by increasing the interaction of surface bridging bonds(hydrogen bonding)and decreasing the repulsive force between colloidal biochar particles.This study showed that LMWOAs could accelerate the aggregation of biochar colloids in acidic or neutral environments and reduce the mobility of biochar colloids in soil rhizosphere.