Ningjie Li

Oxalate production at different initial Pb2+ concentrations and the influence of oxalate during solid-state fermentation of straw with Phanerochaete chrysosporium

The production of oxalate at different initial Pb(2+) concentrations during solid-state fermentation of straw with Phanerochaete chrysosporium was investigated. It was found that the maximal peak value of oxalate concentration (22.84 mM) was detected at the initial Pb(2+) concentration of 200 mg kg(-1) dry straw, while the minimum (15.89 mM) at the concentration of 600 mg Pb(2+)kg(-1) dry straw, and at moderate concentration of Pb(2+) the capability of oxalic acid secretion was enhanced. In addition, it was also found that more oxalic acid accumulation went together with better Pb(2+) passivation effect and higher manganese peroxidase (MnP) activity. The present findings will improve the understandings of the interactions of heavy metals with white-rot fungi and the role of oxalate in lignin degradation system, which could provide useful references for more efficient treatment of Pb-contaminated lignocellulosic waste.

Study of the degradation of methylene blue by semi-solid-state fermentation of agricultural residues with Phanerochaete chrysosporium and reutilization of fermented residues

The degradation of methylene blue (MB) by semi-solid-state fermentation of agricultural residues rice straw with Phanerochaete chrysosporium and the reutilization of fermented residues was investigated. A maximum decolorization of 84.8% for an initial dye concentration of 0.4 g/L was observed at the optimal operating conditions (temperature 35 °C, pH 5). As compared to the previous results obtained using synthetic materials as substrate, the results in the present study revealed an excellent performance of the bioreactor in decolorizing the wastewater containing MB, which is due to this type of cultivation reproducing the natural living conditions of the white rot fungi. Among the two ligninolytic enzymes that are responsible to the decolorization, manganese peroxidase (MnP) activity was found better correlated with decoloration percentage. Our results also provide a first step to recycling the fermented residues for the removal of MB from aqueous solutions, the maximum adsorption capacity of the fermented residues reached 51.4 mg/g.

Combined removal of di(2-ethylhexyl)phthalate (DEHP) and Pb(II) by using a cutinase loaded nanoporous gold-polyethyleneimine adsorbent

A cutinase loaded nanoporous gold-polyethyleneimine (NPG-PEI) was fabricated for the application in simultaneous removal of DEHP and Pb(II) from contaminated water. The thermal stability, acid and alkali resistance, storage stability and reutilization of immobilized cutinase were enhanced. The removal kinetics of DEHP and Pb(II) were described by a pseudo-second-order kinetic model, and the adsorption isotherms for Pb(II) were fitted by a Langmuir model. Pb(II) had a suppression effect on DEHP uptake in the simultaneous removal and DEHP preloading experiments. The overall DEHP removal efficiency was about 90.9%, in which enzymatic hydrolysis contributed about 81.9%, and the enzymatic degradation products of DEHP were mainly non-toxic 1,3-isobenzofurandione (IBF). In simultaneous removal of DEHP and Pb(II) at low concentrations, the cutinase loaded NPG-PEI can be used more than five times before regeneration. Due to its high removal capacity, easy separation and effective reusability, cutinase loaded NPG-PEI presented excellent potential in wastewater treatment.

The Oxidative Stress of Phanerochaete chrysosporium Against Lead Toxicity

Among the technologies for heavy metal remediation, bioremediation technology has gained extensive attention because of its low processing costs and high efficiency. The white-rot fungus Phanerochaete chrysosporium (P. chrysosporium) which has a good tolerance to heavy metals has been widely used in the heavy metal bioremediation. In order to figure out the molecular mechanisms involved in the oxidative stress of P. chrysosporium against metal toxicity, we examined the effect of Pb2+ on the levels of reactive oxygen species and the production of malondialdehyde. Results showed that P. chrysosporium could adjust Pb-stressed condition by regulating the unique oxidation-antioxidation process in cells and kept a balance between oxidation and antioxidation when it was threatened by a different dose of Pb2+. Investigations into the oxidative stress of P. chrysosporium to lead could not only provide a better understanding of the relationship between lead and oxidative stress in P. chrysosporium, but also offer important informations on the development of fungal-based remediation technologies to reduce the toxic effects of lead.

Response of extracellular carboxylic and thiol ligands (oxalate, thiol compounds) to Pb2+ stress in Phanerochaete chrysosporium

When exposed to higher Pb2+ concentration, Phanerochaete chrysosporium secreted higher content of oxalate and thiol compounds. An earlier and faster increase in oxalate was observed after short-term exposure, comparing with a gentle increase in the thiol compounds. In the extracellular polymeric substances (EPS) extract, more oxalate and T-SH were detected when the initial Pb2+ was higher, and the variations were different from the situation in the culture medium. In EPS solution, the oxalate amount was more closely related with Pb than that of thiol compounds. pH condition in the whole Pb removal process by P. chrysosporium ranged from 4 to 6.5 and was more beneficial for the binding of Pb2+ to carboxylic groups in the oxalic acid. More Pb2+ induced more EPS amount, and the increase of EPS amount influenced the immobilized oxalate more seriously. The present study can supply more comprehensive information about the metal passivation mechanism in white-rot fungi and provide meaningful references for an enhanced removal of heavy metals.

Synthesis of gold–cellobiose nanocomposites for colorimetric measurement of cellobiase activity

Gold-cellobiose nanocomposites (GCNCs) were synthesized by reducing gold salt with a polysaccharide, cellobiose. Here, cellobiose acted as a controller of nucleation or stabilizer in the formation of gold nanoparticles. The obtained GCNCs were characterized with UV-visible spectroscopy; Zetasizer and Fourier transform infrared (FT-IR) spectrophotometer. Moreover, 6-Mercapto-1-hexanol (MCH) was modified on GCNCs, and the MCH-GCNCs were used to determine the cellobiase activity in compost extracts based on the surface plasmon resonance (SPR) property of MCH-GCNCs. The degradation of cellobiose on MCH-GCNCs by cellobiase could induce the aggregation, and the SPR absorption wavelength of MCH-GCNCs correspondingly red shifted. Thus, the absorbance ratio of treated MCH-GCNCs (A650/A520) could be used to estimate the cellobiase activity, and the probe exhibited highly sensitive and selective detection of the cellobiase activity with a wide linear from 3.0 to 100.0U L(-1) within 20 min. Meanwhile, a good linear relationship with correlation coefficient of R2=0.9976 was obtained. This approach successfully showed the suitability of gold nanocomposites as a colorimetric sensor for the sensitive and specific enzyme activity detection.

Colorimetric screening of β-glucosidase inhibition based on gold nanocomposites

This article presents a simple gold–cellobiose nanocomposites based colorimetric assay for the screening of β-glucosidase inhibitors. The nanocomposites are composed of gold nanoparticles (AuNPs), particular cellobiose substrates, and 6-mercapto-1-hexanol. After β-glucosidase digestion, the AuNPs become more exposed and the attractive force between AuNPs is increased by the modified 6-mercapto-1-hexanol. Consequently, the aggregation of nanocomposites and the red shift of surface plasmon absorption can be observed. The absorbance ratio at 650 nm and 520 nm (A650/A520) of nanocomposites can be used to estimate the β-glucosidase activity. This technology could serve an alternative platform for the efficient screening of β-glucosidase inhibitors. Both the inhibition effect of heavy metals and surfactants on β-glucosidase could be analyzed by the detection of β-glucosidase activity. To summarize, the goal of this technical note is to develop a simple colorimetric method for the screening of β-glucosidase inhibitors.