Remediation of Chromium-Contaminated Soil Based on Bacillus cereus WHX-1 Immobilized on Biochar: Cr(VI) Transformation and Functional Microbial Enrichment

Microorganisms are applied to remediate chromium (Cr)-contaminated soil extensively. Nevertheless, the microbial loss and growth inhibition in the soil environment restrain the application of this technology. In this study, a Cr(VI)-reducing strain named Bacillus cereus WHX-1 was screened, and the microbial aggregates system was established via immobilizing the strain on Enteromorpha prolifera biochar to enhance the Cr(VI)-reducing activity of this strain. The mechanism of the system on Cr(VI) transformation in Cr-contaminated soil was illuminated. Pot experiments indicated that the microbial aggregates system improved the physicochemical characteristics of Cr-contaminated soil obviously by increasing organic carbon content and cation exchange capacity, as well as decreasing redox potential and bulk density of soil. Moreover, 94.22% of Cr(VI) was transformed into Cr(III) in the pot, and the content of residue fraction Cr increased by 63.38% compared with control check (CK). Correspondingly, the physiological property of Ryegrass planted on the Cr-contaminated soil was improved markedly and the main Cr(VI)-reducing microbes, Bacillus spp., were enriched in the soil with a relative abundance of 28.43% in the microbial aggregates system. Considering more active sites of biochar for microbial aggregation, it was inferred that B. cereus WHX-1 could be immobilized by E. prolifera biochar, and more Cr(VI) was transformed into residue fraction. Cr stress was decreased and the growth of plants was enhanced. This study would provide a new perspective for Cr-contaminated soil remediation.

Viscoelastic properties of tablets from Osborne fractions, pentosans, flour and bread evaluated by creep tests

Little attention has been given to the influence of non-gluten components on the viscoelastic properties of wheat flour dough, bread making process and their products. The aim of this study was to evaluate by creep tests the viscoelastic properties of tablets manufactured from Osborne solubility fractions (globulins, gliadins, glutenins, albumins and residue), pentosans, flour and bread. Hard and soft wheat cultivars were used to prepare the reconstituted tablets. Sintered tablets (except flour and bread) showed similar values to those obtained from the sum of the regression coefficients of the fractions. Gliadins and albumins accounted for about 54% of the total elasticity. Gliadins contributed with almost half of the total viscosity (45.7%), and showed the highest value for the viscosity coefficient of the viscous element. When the effect of dilution was evaluated, the residue showed the highest instantaneous elastic modulus (788.2 MPa). Retardation times of the first element (λ1~ 3.5 s) were about 10 times lower than the second element (λ2~ 39.3 s). The analysis of compliance of data corrected by protein content in flour showed that the residue fraction presented the highest values. An important contribution of non-gluten components (starch, albumins and globulins) on the viscoelastic performance of sintered tablets from Osborne fractions, flour and bread was found.

Speciation Analysis of Heavy Metals of Core Amuta Sediments in Lianhua Lake

The BCR-SEP method was used to determine the binding forms of heavy metals in Amuta Lake(AMT) in this paper. The chemical forms of heavy metals, namely extractable fractions or valid fractions, including exchangeable-carbonate fraction, Fe-Mn oxide fraction and Organic-sulfide fraction .The results of the partitioning study indicated that in the core AMT sediments, Cr, Fe and Ni are mainly associated with the residue fraction, Cu is mainly concentrated in the Fe–Mn oxide fractions and residue fraction, Mn is concentrated in the exchangeable-carbonate fraction and residue fraction. Zn is concentrated in organic-sulfide fraction and residue fraction.

Evaluation of Methanethiol and Dimethyl Disulfide in the Homogenate Fractions of Fresh and Frozen Broccoli Tissues

The emission of methanethiol (MT) and dimethyl disulfide (DMDS) from homogenate fractions of fresh and frozen broccoli tissues was analyzed using gas chromatography coupled with flame photometric detector after incubating for 2 h at 30 °C in a water bath. Both sulfur compounds were detected in the headspace of the residue fraction of fresh broccoli but not frozen tissues. Only DMDS was formed in the filtrate and supernatant fractions of fresh tissues but their emission was also suppressed in frozen tissues. Phosphate buffer treatment reduced the amount of MT formed on the residue of fresh tissues, whereas treatment of enzyme co-factor, pyridoxal phosphate, and its substrate, S-methyl-L-cysteine sulfoxide, in the residue fraction of frozen broccoli did not induce the formation of MT except for DMDS. Both compounds were also inhibited in the residue fraction of the fresh tissues by aminooxyacetic acid, a potential inhibitor of pyridoxal phosphate-dependent enzymes, indicating that these objectionable odors were produced upon the action of cysteine sulfoxide lyase. This enzyme, which yielded strong activity in the residue upon extraction with buffer containing Triton X-100, is highly likely to be a bound enzyme. Inhibition of MT and DMDS in frozen broccoli tissues is likely attributed to the retardation of the enzyme action due in part to the loss of the co-factor and its substrate, and owing to the solubility of MT and its affinity to gaseous condition.

Estimation of Slow- and Fast-Cycling Soil Organic Carbon Pools from 6N HCl Hydrolysis

Acid hydrolysis is used to fractionate the soil organic carbon pool into relatively slow- and fast-cycling compartments on soils from Arizona, the Great Plains states and Michigan collected for carbon isotope tracer studies related to soil carbon sequestration, for studies of shifts in C3/C4 vegetation, and for “pre-bomb” soil-carbon inventories. Prior to hydrolysis, soil samples are first treated with cold 0.5–1N HCl to remove soil carbonates if necessary. Samples are then dispersed in a concentrated NaCl solution (ρ≍1.2 g cm-3) and floated plant fragments are skimmed off the surface. After rinsing and drying, all remaining recognizable plant fragments are picked from the soil under 20x magnification. Plant-free soils, and hot, 6N HCl acid-hydrolysis residue and hydrolyzate fractions are analyzed for carbon content, δ13C and 14C age, and the carbon distribution is verified within 1–2% by stable-carbon isotope mass balance. On average, the recalcitrant residue fraction is 1800 yr older and 2.6% more 13C-depleted than total soil organic carbon. A test of hydrolysis with fresh plant fragments produced as much as 71–76% in the acid-hydrolysis residue pool. Thus, if plant fragments are not largely removed prior to hydrolysis, the residue fraction may date much younger than it actually is.