Biosorption of silver ions onto Bacillus cereus biomass was investigated. Overall kinetic experiments were performed for the determination of the necessary contact time for the attainment of equilibrium. It was found that the overall biosorption process was best described by pseudo second-order kinetic model. The crystals detected by scanning electron microscope and X-ray photoelectron spectroscopy suggested the precipitation was a possible mechanism of biosorption. The molecular genetics of silver resistance of B. cereus biomass was also detected and illustrated by a whole cell sensor tool.
Li Li Qing Hu Jinghai Zeng Hongyan Qi Guoqiang Zhuang
Fungicides have been used extensively for controlling fungal pathogens of plants. However, little is known regarding the effects that fungicides upon the indigenous bacterial communities within the plant phyllosphere. The aims of this study were to assess the impact of fungicide enostroburin upon bacterial communities in wheat phyllosphere. Culture-independent methodologies of 16S rDNA clone library and 16S rDNA directed polymerase chain reaction with denaturing gradient gel electrophoresis （PCR-DGGE） were used for monitoring the change of bacterial community. The 16S rDNA clone library and PCR-DGGE analysis both confirmed the microbial community of wheat plant phyllosphere were predominantly of the γ-Proteobacteria phyla. Results from PCR-DGGE analysis indicated a significant change in bacterial community structure within the phyllosphere following fungicide enostroburin application. Bands sequenced within control cultures were predominantly of Pseudomonas genus, but those bands sequenced in the treated samples were predominantly strains of Pantoea genus and Pseudomonas genus. Of interest was the appearance of two DGGE bands following fungicide treatment, one of which had sequence similarities （98%） to Pantoea sp. which might be a competitor of plant pathogens. This study revealed the wheat phyllosphere bacterial community composition and a shift in the bacterial community following fungicide enostroburin application.
Immigrant bacteria located on leaf surfaces are important to the health of plants as well as to people who consume fresh fruits and vegetables. However, the spatial distribution and organization of these immigrant bacteria on leaf surfaces are still poorly understood. To examine the spatial organization of these strains, two bacterial strains on tobacco leaves： （1） an indigenous strain, Pseudomonas stutzeri Nov. Y2011 labeled with green fluorescent protein, and （2） an immigrant strain Pantoea agglomerans labeled with cyan fluorescent protein isolated from pear, were studied. Under moist conditions, P. agglomerans cells quickly disappeared from direct observation by laser- scanning confocal microscopy, although elution results indicated that large amounts of live cells were still present on the leaves. Following exposure to desiccation stress, particles of cyan fluorescent protein-labeled P. agglomerans were visible within cracked aggregates of P. stutzeri Nov. Y2011. Detailed observation of sectioned aggregates showed that colonies of immigrant P. agglomerans were embedded within aggregates of P. stutzeri Nov. Y2011. Furthermore, carbon-resource partitioning studies suggested that these two species could coexist without significant nutritional competition. This is the first observation of an immigrant bacterium embedding within aggregates of indigenous bacteria on leaves to evade harsh conditions in the phyllosphere.
The prediction and assessment of environmental pollution by arsenic are important preconditions of advocating environmental protection and human health risk assessment. A yellow fluorescent protein-based whole-cell biosensor for the detection of arsenite and arsenate was constructed and tested. An arsenic-resistant promoter and the regulatory gene arsR were obtained by PCR from the genome ofEscherichia coli DH5ct, andphiYFP was introduced into E. coli DH5ct as a reporter gene to construct an arsenic-resistant whole-cell biosensor （WCB-11） in which phiYFP was expressed well for the first time. Experimental results demonstrated that the biosensor has a good response to arsenic and the expression ofphiYFP. When strain WCB-11 was exposed to As^3＋ and As^5＋, the expression of yellow fluorescence was time-dependent and dose-dependent. This engineered construct is expected to become established as an inexpensive and convenient method for the detection of arsenic in the field.
Qing Hu ,Li Li,Yanjuan Wang,Wenjuan Zhao,Hongyan Qi,Guoqiang Zhuang Department of Environmental Bio-Technology,Research Center for Eco-Environmental Sciences,Chinese Academy of Sciences,Beijing 100085,China.
