Environmental fate of Bt proteins in soil: Transport, adsorption/desorption and degradation.

During the production and application of Bacillus thuringiensis (Bt) transgenic crops, large doses of insecticidal Bt toxic proteins are expressed continuously. The multi-interfacial behaviors of Bt proteins entering the environment in multi-media affects their states of existence transformation, transport and fate as well as biological and ecological impacts. Because both soil matrix and organisms will be exposed to Bt proteins to a certain extent, knowledge of the multi-interfacial behaviors and affecting factors of Bt proteins are vital not only for understanding the source-sink distribution mechanisms, predicting their bio-availability, but also for exploring the soil safety and environmental problems caused by the interaction between Bt proteins and soil matrix. This review summarized and analyzed various internal and external factors that affect the adsorption/ desorption and degradation of Bt proteins in the environment, so as to understand the multi-interfacial behaviors of Bt proteins. In addition, the reasons of concentration changes of Bt proteins in soil are discussed. This review will also discuss the existing knowledge of the combined effects of Bt proteins and other pollutants in environment. Finally, discussing the factors that should be considered when assessing the environmental risk of Bt proteins, thus to further improve the understanding of the environmental fate of Bt proteins.

Exploring the interaction between Cry1Ac protein and Zn2+, Cd2+ metal ions by fluorescence quenching and molecular docking approaches.

Bacillus Thuringiensis (Bt) protein has a strong ability to complex with metal ions, which may increase the transport of metal ions in the soil multi-media system. In this study, the interactions between Cry1Ac protein and metal ions (Zn2+ and Cd2+) were investigated through spectroscopies and molecular docking methods. The spectra results showed that both Zn2+ and Cd2+ quenched the fluorescence intensity of Cry1Ac protein through the static quenching. The binding constants with 4-5 orders of magnitude also indicated the interactions between the ions and the Cry1Ac protein. The thermodynamic analysis showed that hydrogen bonds and van der Waals forces were predominant during the processes. In terms of the Förster non-radiation energy transfer theory, the binding distances between metal ions and Cry1Ac protein were approximately 0.21-0.24 nm, indicating the existence of a non-radiative energy transfer between them. Furthermore, molecular docking revealed that the metal ions participated in ligand binding with the Cry1Ac at the locations Asp569, Thr560, Asn564 and Gln566. The present work provided reasonable models helping us further understand the transport effect of heavy metals in the presence of Cry1Ac. The results could provide mechanistic insights into the nature of metal ions-Cry1Ac interactions and offer important information on the toxicity risk of metal ions-Cry1Ac binding interactions.

Biodelignification of rice straw by Phanerochaete chrysosporium in the presence of dirhamnolipid.

Lignin degradation by white-rot fungi has received considerable attention as a means for reducing accumulation of lignocellulosic wastes in the environment. The stimulatory effect of surfactants on fungal lignocellulose bioconversion also has attracted wide interest. In this study the influence of dirhamnolipid biosurfactant on biodegradation of rice straw by Phanerochaete chrysosporium was investigated. It was shown that the biodelignification process of rice straw can be significantly enhanced by the presence of dirhamnolipid biosurfactant. In particular, the dirhamnolipid at the concentration of 0.007% increased the peak activity of lignin peroxidase (LiP) by 86% without affecting the manganese peroxidase (MnP) activity. The water-soluble organic carbon (WSOC) contents in the straw substrates as well as the microbial growth and activity were effectively improved by dirhamnolipid, while the degradation rate of lignin increased by 54% with dirhamnolipid of 0.007%. Observed chemical structural and morphological changes showed that the straw substrates were delignified in the presence of dirhamnolipid with the formation of terrace-like fragments separated from the inner cellular fibers and the release of simple compounds. Variation partitioning analysis revealed that the dirhamnolipid addition induced a significant straw biodelignification which explained 22.1% (P = 0.013) of the variance.

The factors affecting a native obligate parasite, Cuscuta australis, in selecting an exotic weed, Humulus scandens, as its host.

In weed management, using native parasites to control exotic weeds is considered a better alternative than classical biological control. But the risk must be assessed because of the potential damage caused by these agents. We conducted this project to investigate the mechanism driving the choice of a native obligate parasite, Cuscuta australis, between the exotic, Humulus scandens, and native plants as its host through field and pot experiments. The results showed that C. australis preferred the exotic weed over native (naturalized) hosts and caused a notable reduction in the biomass of H. scandens in the field. In contrast, the results of the pot experimentindicated that C. australis preferred a mix of native (naturalized) hosts over the exotic weed. Both texperiments indicated that the parasitic preference of C. australis was induced more by light irradiance than plant water, carbon (C), nitrogen (N) and phosphorus (P) contents, indicating that the native parasite can only be used to control H. scandens when the exotic weed forms mono-cultures or dominates the community. Accordingly, induction and release of C. australis to control H. scandens should be conducted with great caution.

Cry1Ab-expressing rice did not influence expression of fecundity-related genes in the wolf spider Pardosa pseudoannulata.

The impact of Bacillus thuringiensis (Bt) toxin proteins on non-target predatory arthropods is not well understood at the cellular and molecular levels. Here, we investigated the potential effects of Cry1Ab expressing rice on fecundity of the wolf spider, Pardosa pseudoannulata, and some of the underlying molecular mechanisms. The results indicated that brown planthoppers (BPHs) reared on Cry1Ab-expressing rice accumulated the Cry toxin and that reproductive parameters (pre-oviposition period, post-oviposition stage, number of eggs, and egg hatching rate) of the spiders that consumed BPHs reared on Bt rice were not different from those that consumed BPHs reared on the non-Bt control rice. The accumulated Cry1Ab did not influence several vitellin (Vt) parameters, including stored energy and amino acid composition, during one generation. We considered the possibility that the Cry toxins exert their influence on beneficial predators via more subtle effects detectable at the molecular level in terms of gene expression. This led us to transcriptome analysis to detect differentially expressed genes in the ovaries of spiders exposed to dietary Cry1Ab and their counterpart control spiders. Eight genes, associated with vitellogenesis, vitellogenin receptor activity, and vitellin membrane formation were not differentially expressed between ovaries from the treated and control spiders, confirmed by qPCR analysis. We infer that dietary Cry1Ab expressing rice does not influence fecundity, nor expression levels of Vt-associated genes in P. pseudoannulata.

[Enzymatic hydrolysis of cellulose in reverse micelles].

Several types of surfactants were adopted to construct reverse micelles, in order to investigate the characteristics of cellulose hydrolysis, we used the carboxymethyl cellulose as substrate. The electrical conductivity was measured to determine the maximum water solubilization W0( W0 = [H2O]/[SA] ) of CTAB, SDS, Tween-80 and rhamnolipid reverse micellar systems were 15.2, 20.1, 2.3 and 40.3. In this condition we studied the effects of surfactants concentrations and cellulose dosage on the enzymatic hydrolysis of reverse micelle,and compared with aqueous systems. It was shown by the results that when the cellulose dosage was 0.15 FPU/g substrate, the maximum yield of reducing sugar in reverse micelles was obtained at 1 cmc of CTAB, SDS, Tween-80 and rhamnolipid, in which the rhamnolipid yield was the highest of 198.03 mg substrate. When the concentrations of CTAB, SDS, Tween-80 and rhamnolipid were 1 cmc, the productions of reverse micelles systems were higher than that of aqueous systems of 34.36%, 21.24%, 11.44% and 34.62%. In the optimum conditions of the surfactant concentration, taking the saving cost and sugar yield into consideration, the cellulose dosage of 5 FPU substrate was the most suitable. The reducing sugar's yield of biosurfactant rhamnolipid reverse micellar system was higher than those of three chemical surfactant systems, it was shown that the adoption of biosurfactant has technologically promising prospect in constructing reverse micelles and enhancing the stability of reverse micelles.

[Feasibility of treatment of landfill leachates by external loop three phase fluidized bed-constructed wetland system].

In this study, the system composed with the external loop fluidized bed reactor and constructed wetland was used to treat the landfill leachate. The change of water quality for the landfill leachate treated by this system was investigated. The experimental results indicated that the COD and NH4(+) -N of the influent reduced from 4000 mg x L(-1) and 300 mg x L(-1) to 1 500 mg x L(-1) and 150 mg x L(-1) after the external loop three phase fluidized bed reactor and steady at 200 mg x L(-1) and 10 mg x L(-1) behind treated by the constructed wetland. The heavy metals of Cd, Zn, Pb were also reduced for treatment by external loop three phase fluidized bed reactor. They were steady at 0.01 mg x L(-1), 0.5 mg x L(-1), 0.1 mg x L(-1) from 0.12 mg x L(-1), 3.0 mg x L(-1), 1.4 mg x L(-1) because of the constructed wetland. We also compared the different plants for the efficiency, the results showed that whatever plants, there was little effects on the efficiency of the COD and NH4(+) -N, but the effect of heavy metal was markedness.

[Biofilm formation in an external loop three phase fluidized bed reactor].

The experiment on biofilm formation in an external loop three phase fluidized bed reactor was presented in this paper. The effect of the value of sludge addition and C/N ratio were studied. The experiment result showed that at the temperature of 20-30 degrees C, when the diameter of granular activated carbon was 0.125-0.5 mm, the value of sludge addition at 2 g x L(-1) was more propitious to the formation of biofilm than 5 g x L(-1). Formation of biofilm in fluidized bed was the rapidest when C/N ratio was between 8-12. It was difficult and leaned to form filamentous bulking sludge when C/N > or = 14. On the basis of the success of attached film, the influence of hydraulic residence time (HRT) on the value of suspended sludge and the value of biofilm was studied. The result showed that while HRT expended and the value of suspended sludge increased, the value of biofilm also increased, when HRT was between 1-3 h. But when HRT exceeded 5h, HRT expended and the value of biofilm decreased. when HRT was between 4-5 h, the value of suspended sludge and the value of biofilm were steady.