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Polychlorinated biphenyls (PCBs) are the typical persistent organic pollutants (POPs) in the environment. As a ubiquitous attenuation course of chlorinated organic compounds in anoxic environment, the microorganism-mediated reductive dechlorination process plays an important role in PCBs transformation, especially the transformation of higher chlorinated PCBs. The higher chlorinated PCBs can be dechlorinated in anaerobic condition, and thus, their persistence and toxicity can be decreased. The resultant lower chlorinated PCBs from the dechlorination can be further degraded and completely mineralized in aerobic condition. This paper summarized the research advances of PCBs microbial reductive dechlorination, introduced the mechanisms and characteristics of the dechlorination and the related specific microorganisms, and approached the affecting factors of PCBs bio-dechlorination, as well as the significances of anaerobic dechlorination coupling with aerobic degradation. The future research directions, including the complex metabolic networks of dechlorinating microbial populations, the screening of novel specific dechlorinators and their practical applications in the remediation of PCBs contaminated sites were also prospected.

Persistent organic pollutants have increasingly become a critical environmental concern, while thermophiles have the high potential of degrading various kinds of environmental organic pollutants. At high temperatures, thermophiles have higher metabolic activity, and the competition by mesophiles is reduced, meanwhile, the solubility and bioavailability of some persistent organic pollutants are greatly increased, and thus, the degradation of the pollutants by thermophiles is more rapid and complete. Therefore, thermophils are of great significance for the bio-treatment of organic wastewater and the bioremediation of organic pollutants-contaminated sites. This paper introduced the research progress on the degradation of organic pollutants by thermophiles in terms of the characteristics of thermophiles in degrading organic pollutants, the effects of temperature on the degradation, the degradation pathways, the degradation enzymes, their coding genes, and practical engineering applications. The future research directions including the degradation mechanisms of thermophiles, their resources reserve, related technology strategies and their applications were also prospected.

Soil microbial indicator is one of the important biological indicators in evaluating the extent of soil contamination. In recent years, with the development of molecular biology, many studies have focused on the ecological functions of soil microorganisms by using metagenomics, metatranscriptome and metaproteomics. Relative to metagenomics and metatranscriptome, soil metaproteomics aims to investigate the spatial and temporal changes of the proteins extracted from soil as well as the functional components of soil microbial genomic expression products, which is more conclusive to explore the ecological functions of soil microbes and their roles in soil pollutants transportation and transformation. Therefore, soil metaproteomics has great potential in soil pollution assessment. Currently, soil metaproteomics is still at its infancy stage, while soil protein extraction method is one of the key factors restraining the potential application of soil metaproteomics. In this paper, the advantages and disadvantage of soil metaproteomics in soil pollution assessment were reviewed, with the focus on the comparison of different soil protein extraction methods. In combining with case studies, the feasibility and limits of soil proteins as an indicator for soil pollution assessment were analyzed. In addition, the future research perspectives on the development of soil metaproteomics were discussed.

Taking non-transgenic parental rice as the control, and by using 13C pulse-chase labeling method coupled with phospholipid fatty acid (PLFA) analysis, this paper studied the effects of transgenic Bt rice on the microbial diversity in rhizosphere soil. The results showed that in the rhizosphere soils of transgenic Bt rice and its non-transgenic parent, saturated PLFAs and branched PLFAs were the main, followed by monounsaturated PLFAs, and polyunsaturated PLFAs. A significantly lower amount of Gram-positive bacterial PLFAs and a higher amount of Gram-negative bacterial PLFAs were observed in the rhizosphere soil of transgenic Bt rice at its seedling, booting, and heading stages, as compared with the control. In the whole growth period of rice, transgenic Bt gene had no significant effects on the fungal and actinomycete PLFAs in rhizosphere soil, and no significant difference was observed in the rhizosphere soil 13C-PLFA content between transgenic Bt rice and its non-transgenic parent. These findings indicated that the insertion of exogenous cry1Ab gene into rice only had temporary effects on the microbial community composition in the rhizosphere soil of rice.

A pot experiment was conducted to study the microbial activity and community structure in a lead-polluted paddy soil under effects of amendment with different concentration sodium thiosulfate. The amendment of the sulfur-containing substrate increased the soil oxidation-reduction potential and respiration rate, promoted the growth of soil sulfur-oxidizing bacteria, and induced some changes in soil microbial community structure. The clone sequencing indicated that the specific bands of soil microbes in sodium thiosulfate treatments had very high similarity to Bateroidetes, Thiobacillus, beta-proteobacteria, and Acidobacteria. Significant changes were observed in the contents of soil carbonate- and Fe/Mn oxide- bound Pb after the amendment of sodium thiosulfate.

Photosynthetic assimilation of CO2 is a primary source of carbon in soil and root exudates and can influence the community dynamics of rhizosphere organisms. Thus, if carbon partitioning is affected in transgenic crops, rhizosphere microbial communities may also be affected. In this study, the temporal effects of gene transformation on carbon partitioning in rice and rhizosphere microbial communities were investigated under greenhouse conditions using the 13C pulse-chase labeling method and phospholipid fatty acid (PLFA) analysis. The 13C contents in leaves of transgenic (Bt) and nontransgenic (Ck) rice were significantly different at the seedling, booting and heading stages. There were no detectable differences in 13C distribution in rice roots and rhizosphere microorganisms at any point during rice development. Although a significantly lower amount of Gram-positive bacterial PLFAs and a higher amount of Gram-negative bacterial PLFAs were observed in Bt rice rhizosphere as compared with Ck at all plant development stages, there were no significant differences in the amount of individual 13C-PLFA between Bt and Ck rhizospheres at any growing stage. These findings indicate that the insertion of cry1Ab and marker genes into rice had no persistent or adverse effect on the photosynthate distribution in rice or the microbial community composition in its rhizosphere.

Methane is the second largest contributor after carbon dioxide to global warming, while landfill is considered as one of the major sources of methane emission, accounting for 1.5%-15% of the global methane sources. Methanotrophic microorganisms play an important role in regulating global methane content, and landfill cover soil is proved to have high capacity of methane oxidation. The study of methanotrophic microorganisms in landfill cover soil and their mechanisms in methane oxidation becomes one of the hot research fields in environmental science and applied microbiology. This review summarized the recent progress on the research of methanotrophic microorganisms, mechanisms and dynamics of microbial methane oxidation, co-metabolism of methane and trace landfill gases, and environmental factors affecting methane oxidation in landfill cover soil. Some perspectives for further research on methanotrophic microorganisms in landfill cover soil were discussed.

All the regulations that define a maximum concentration of metals in the receiving soil are based on total soil metal concentration. However, the potential toxicity of a heavy metal in the soil depends on its speciation and availability. We studied the effects of heavy metal speciation and availability on soil microorganism activities along a Cu/Zn contamination gradient. Microbial biomass and enzyme activity of soil contaminated with both Cu and Zn were investigated. The results showed that microbial biomass was negatively affected by the elevated metal levels. The microbial biomass-C (C(mic))/organic C (C(org)) ratio was closely correlated to heavy metal stress. There were negative correlations between soil microbial biomass, phosphatase activity and NH4NO3 extractable heavy metals. The soil microorganism activity could be predicted using empirical models with the availability of Cu and Zn. We observed that 72% of the variation in phosphatase activity could be explained by the NH4NO3-extractable and total heavy metal concentration. By considering different monitoring approaches and different viewpoints, this set of methods applied in this study seemed sensitive to site differences and contributed to a better understanding of the effects of heavy metals on the size and activity of microorganisms in soils. The data presented demonstrate the relationship between heavy metals availability and heavy metal toxicity to soil microorganism along a contamination gradient.

The role of rhizosphere bacteria in facilitating the solubility of copper (Cu) in contaminated soil and Cu accumulation in plant were studied. The bacteria strains were isolated from the rhizosphere of Elsholtzia splendens, a Cu accumulator growing on Tonglu Mountain copper mines. After the sandy soils containing 237 mg kg(-1) were incubated with the bacteria strains, it was indicated that rhizosphere microbes played an important role in influencing the availability of water-soluble Cu in soils. Soils had greater concentrations of water-extractable Cu compared with axenic soils inoculated with different bacterial strains. Further evidence for bacterial facilitation of increased solubility of Cu in the soil was obtained using the antibiotic ampicillin (0.1 mg g(-1)). There were 36% decreases in Cu concentration in the presence of bacterial strain MS12 and ampicillin together compared with bacterial inoculation alone. Different bacterial strains had different abilities on soil water-soluble Cu. To achieve the highest rates of plant Cu accumulation, it was necessary for bacteria to be present in the rhizosphere of E. splendens. Inoculated plants supplied with 20 micromol L(-1) CuSO4 had significantly greater concentrations of Cu in shoots and roots than uninoculated plants and bacterial strain MS2 was the most effective strain in promoting plant Cu uptake. There were 2.2-fold and 2.5-fold increases in Cu accumulation in the shoots and roots of plants inoculated with strain MS2 compared to axenic controls. Furthermore, when ampicillin and the bacterial strains were added together to the nutrient solution, the Cu concentrations in roots and shoots of ampicillin-treated plants were lower than those in inoculated plants. When ampicillin was added to the nutrient solution, Cu accumulation was inhibited by about 24-44% in shoots and 20-44% in roots. The above results provided a new insight into the phytoremediation of Cu-contaminated soil.

A greenhouse experiment was carried out to compare differences in potential activities of ammonification, nitrification and denitrification in rhizosphere and bulk soil in a heavy-metal-stressed system. Exchangeable fractions of Cd, Cu and Cr were all higher in the rhizosphere of maize than in bulk soil. Results showed that the mineralization of N in soil was stimulated by low concentration of Cd. Addition of Cd at low levels stimulated the ammonifying and nitrifying activity in soil, while inhibitory influences were shown at high levels. Nitrifying bacteria was proved to be the most sensitive one, whilst the effect on denitrifying bacteria was very limited. Comparing Cd, Cu and Cr(VI) at 20 mg/kg soil, Cd was the most effective inhibitor of ammonification and denitrification, while Cr(VI) had the strongest inhibitory influence on nitrifying activity. Root exudates played important roles on the different exchangeable metal fractions and bacterial activities between rhizosphere and non-rhizosphere. Nitrate was the main form of mineral N in soil, as well as the main form of N absorbed by plants, but the formation and relative absorption of ammonium were promoted in response to high Cd exposure.