Exploring the characteristics of microbial community and enzyme activity in the aged refuse landfill environment of Taiyuan,China

Municipal solid waste landfill is the main disposal option for domestic garbage,in which microbial activities play an important role.However,despite the widespread practice of landfilling,the metagenomic microbial profiles of landfill sites remain poorly characterized.In this study,we used a combination of physicochemical analysis,ultraviolet-visible spectrophotometry,and high-throughput Illumina shotgun sequencing to systematically investigate the changes in soil enzyme activities,microbial community structure,and functional attributes in aged refuse collected from the Xingou Municipal Solid Waste Landfill in Taiyuan,China,with ordinary topsoil from an area within 5 km of the landfill as control soil.Except for neutral phosphatase(P=0.065),the activities of urease,laccase,dehydrogenase,sucrase,neutral protease,andβ-glucosidase were all significantly reduced(P<0.05)in the aged refuse compared with the control soil.Contrastingly,catalase activity was found to be significantly elevated in the aged refuse.Compared with the control soil,aged refuse was characterized by higher richness and diversity of microbial communities,as reflected by the higher values of community richness estimators(Chao 1 and ACE)and diversity indices(Shannon and Simpson).In total,186 phyla,4354 genera,and 34459 species were identified,with 132 phyla,1914 genera,and7369 species showing significantly different abundances between the aged refuse and the control soil.Actinobacteria and Acidobacteria were identified as the dominant phyla in the control soil,whereas Proteobacteria,Euryarchaeota(archaea),and Firmicutes were found to predominate in the aged refuse.Notably,Euryarchaeota and Methanoculleus were the major taxa detected in the aged refuse,but were almost completely absent in the control soil.Xenobiotic biodegradation and bacterial chemotaxis were the main functions of the microflora in the aged refuse,whereas the carbohydrate,amino acid,energy,and lipid metabolism pathways were significantly enriched in the control soil.Moreover,the aged refuse contained a high abundance of genes involved in quorum sensing.Our findings in this study revealed close associations between enzyme activities and variations in the microbial community structure and genes that were actively involved in biodegradation activities at landfill sites.It was found that the landfill environment was characterized by a more complex spectrum of microbial activities than expected.Further investigations are needed to gain a more comprehensive understanding of the microbial community structure and functional attributes as well as their potential influencing factors in the landfill environment.

Effects of nitrogen dioxide and its acid mist on reactive oxygen species production and antioxidant enzyme activity in Arabidopsis plants

Nitrogen dioxide（NO2） is one of the most common and harmful air pollutants. To analyze the response of plants to NO2 stress, we investigated the morphological change, reactive oxygen species（ROS） production and antioxidant enzyme activity in Arabidopsis thaliana（Col-0） exposed to 1.7, 4, 8.5, and 18.8 mg/m3NO2. The results indicate that NO2 exposure affected plant growth and chlorophyll（Chl） content, and increased oxygen free radical（O2-）production rate in Arabidopsis shoots. Furthermore, NO2 elevated the levels of lipid peroxidation and protein oxidation, accompanied by the induction of antioxidant enzyme activities and change of ascorbate（As A） and glutathione（GSH） contents. Following this, we mimicked nitric acid mist under experimental conditions, and confirmed the antioxidant mechanism of the plant to the stress. Our results imply that NO2 and its acid mist caused pollution risk to plant systems. During the process, increased ROS acted as a signal to induce a defense response, and antioxidant status played an important role in plant protection against NO2/nitric acid mist-caused oxidative damage.