Remediation of toxic metals by bacteria offers a relatively inexpensive and efficient way for the decontamination of soil and associated environments. The present study was carried out to investigate the surface characteristics, adsorption, and remobilization of Cd and Cu on bacteria and their composites with soil colloidal components, which are the most active constituents in soils. The bacterial strain NTG-01 (Enterobacter aerogenes), which was both Cd-and Cu-resistant, was isolated from a heavily Cu-contaminated soil of the mining area in Daye suburb of Hubei Province, China. Batch laboratory experiments with NTG-01 and soil colloids were performed to quantify adsorption of Cu and Cd. The surface area of kaolinite and the soil colloids from an Alfisol and Ultisol increased by 3.0-8.8% after the introduction of the bacteria. In the presence of bacterial cells, the negative charges of soil colloid systems increased and the positive charges decreased, shifting pH from 4.0 to 6.5. Our results demonstrate that bacteria promote the adsorption of Cd and Cu by kaolinite and soil colloid systems. However, the heavy metals bound by the bacterial composites could also be easily released by NH4NO3 and EDTA. Caution should be taken when using such bacterial strains in bioremediation of heavy metalcontaminated soils.

Soybean rhizobia and their biodiversities were studied based on a systematicinvestigation of microbial flora at different altitudes of Shennongjia, a forest reserve incentral China. The objectives of this work were to investigate the distribution and thegenetic variation of the indigenous soybean rhizobia in an unexploited virgin forest withno soybean-planting history, and to employ this biodiversity to improve innoculantstrains that are applied to increase biological nitrogen fixation of soybean. Samples werecollected respectively from the soils at 500, 1,060, 1,500, 1,950, 2,400 and 3,100 metersabove sea level in Shennongjia Forest Reserve. Their corresponding pHs were 5.50, 4.91, 5.64, 5.28, 5.49 and 4.60. Results showed that the number of microorganisms in all thesoil samples studied followed the order: bacteria>actinomyces>fungi. Soybean rhizobiawere isolated only from the soils above elevations of 1,500 meter. A total of 25 strainswere isolated using the plant trap method with four different trapping plants. They wereall Sinorhizobium fredii. Their genetic biodiversities were characterized by 16S-23SrDNA intergenic region PCR-RFLP and RAPD analysis. After having been washed twotimes, bacterial suspensions were used as a template for the PCR amplification. Onepair of opposite highly conserved 16S and 23S ribosomal primerspHr(rev) andp23SR01 were used to amplify the intergenic region between 16S and 23S rDNA byPCR. All the tested strains produced a 2.1Kb 16S-23S rDNA fragment. After digestionwith three restriction enzymes (HaeIII, MspI and CfoI) respectively, several differentrestriction patterns were observed. Great variations in 16S-23S RFLP-patterns wereobserved. The tested S. fredii strains could be differentiated in eleven differentgenotypes. Then twelve primers were applied to RAPD analysis and a dendrogram wasobtained. These isolates showed a great diversity. Since Shennongjia is an unexploitedforest region in central China and the gene center of soybean is located in China, thesymbiotic genes harbored by these strains may be of great importance. Further studiesto characterize these isolates are being carried out.

The adsorption and binding of plasmid p34S DNA on four different colloidal fractions from a Brown soil and clay minerals in the presence of various Ca2+ concentrations, the ability of bound DNA to transform competent cells of CaCl2-treated Escherichia coli, and the resistance of bound DNA to degradation by DNase I were studied. DNA adsorption on soil colloids and clay minerals was promoted in the presence of Ca2+. Kaolinite exhibited the highest adsorption affinity for DNA among the examined soil colloids and clay minerals. In comparison with organo-mineral complexes (organic clays) and fine clays (0.02mm), DNA was tightly adsorbed by H2O2-treated clays (inorganic clays) and coarse clays (0.2-2mm). The transformation efficiency of bound DNA increased with increasing concentrations of Ca2+at which soil colloid or clay mineral-DNA complexes were formed. DNA bound by kaolinite showed the lowest transformation efficiency, and especially no transformants were observed with kaolinite-DNA complex prepared at 5-100mM Ca2+. Compared to organic clays and fine clays, DNA bound on inorganic clays and coarse clays showed a lower capacity to transform E. coli at different Ca2+ concentrations. The presence of soil colloids and minerals provided protection to DNA against degradation by DNase I. Montmorillonite, organic clays and fine clays showed stronger protective effects for DNA than inorganic clays and coarse clays. The protection mechanisms as well as the differences in transforming efficiency of plasmid DNA molecules bound on various soil colloidal particles are discussed. The information obtained in this study is of fundamental significance for the understanding of the horizontal dissemination of recombinant DNA and the fate of extracellular DNA in soil environments.

Adsorption of Pseudomonas putida on minerals including montmorillonite, kaolinite and goethite was studied. The adsorption isotherms of P. putida on the examined minerals conformed to the Langmuir equation. The amount of P. putida adsorbed followed the order: goethite>kaolinite>montmorillonite. A greater extent of P. putida adsorption on minerals was observed in the range of temperature from 15 to 35℃. The adsorption of P. putida on minerals decreased with the increase of pH from 3.0 to 10.0. Magnesium ion was more efficient than sodium ion in promoting P. putida adsorption on minerals. The results suggest that electrostatic interactions play a vital role in P. putida adsorption by soil colloidal factions. The information obtained in this study is of fundamental significance for the understanding of the survival and transport of bacteria in soil systems.

3’-Phosphoadenosine-5’-phosphatase (PAPase) is required for the removal of toxic 3’-phosphoadenosine- 5’-phosphate (PAP) produced during sulfur assimilation in various eukaryotic organisms. This enzyme is a well-known target of lithium and sodium toxicity and has been used for the production of salt-resistant transgenic plants. In addition, PAPase has also been proposed as a target in the treatment of manic-depressive patients. One gene, halA, which could encode a protein closely related to the PAPases of yeasts and plants, was identified from the cyanobacterium Arthrospira (Spirulina) platensis. Phylogenic analysis indicated that proteins related to PAPases from several cyanobacteria were found in different clades, suggesting multiple origins of PAPases in cyanobacteria. The HalA polypeptide from A. platensis was overproduced in Escherichia coli and used for the characterization of its biochemical properties. HalA was dependent on Mg2+for its activity and could use PAP or 3’-phosphoadenosine-5’-phosphosulfate as a substrate. HalA is sensitive to Li+ (50% inhibitory concentration [IC50=3.6mM) but only slightly sensitive to Na (IC50=600mM). The salt sensitivity of HalA was thus different from that of most of its eukaryotic counterparts, which are much more sensitive to both Li+ and Na+, but was comparable to the PAPase AtAHL (Hal2p-like protein) from Arabidopsis thaliana. The properties of HalA could help us to understand the structure-function relationship underlying the salt sensitivity of PAPases. The expression of halA improved the Li+ tolerance of E. coli, suggesting that the sulfur-assimilating pathway is a likely target of salt toxicity in bacteria as well.