Molecular analysis of microbial community in a groundwater sample polluted by landfill leachate and seawater.

Seashore landfill aquifers are environments of special physicochemical conditions (high organic load and high salinity), and microbes in leachate-polluted aquifers play a significant role for intrinsic bioremediation. In order to characterize microbial diversity and look for clues on the relationship between microbial community structure and hydrochemistry, a culture-independent examination of a typical groundwater sample obtained from a seashore landfill was conducted by sequence analysis of 16S rDNA clone library. Two sets of universal 16S rDNA primers were used to amplify DNA extracted from the groundwater so that problems arising from primer efficiency and specificity could be reduced. Of 74 clones randomly selected from the libraries, 30 contained unique sequences whose analysis showed that the majority of them belonged to bacteria (95.9%), with Proteobacteria (63.5%) being the dominant division. One archaeal sequence and one eukaryotic sequence were found as well. Bacterial sequences belonging to the following phylogenic groups were identified: Bacteroidetes (20.3%), beta, gamma, delta and epsilon-subdivisions of Proteobacteria (47.3%, 9.5%, 5.4% and 1.3%, respectively), Firmicutes (1.4%), Actinobacteria (2.7%), Cyanobacteria (2.7%). The percentages of Proteobacteria and Bacteroides in seawater were greater than those in the groundwater from a non-seashore landfill, indicating a possible influence of seawater. Quite a few sequences had close relatives in marine or hypersaline environments. Many sequences showed affiliations with microbes involved in anaerobic fermentation. The remarkable abundance of sequences related to (per)chlorate-reducing bacteria (ClRB) in the groundwater was significant and worthy of further study.

Variations of dominant microbial populations in groundwater in response to the leachate from Laogang Landfill.

Temporal changes of dominant microbial populations in groundwater in response to the leachate from Shanghai Laogang Landfill were investigated. Concentrations of dissolved redox-relevant species in groundwater suggested that the dominating redox process had changed from denitrification to methane-production/sulfate-reduction due to landfilling. Dominant microbial populations were determined using restriction fragment length polymorphism( RFLP) analyses of 16S rRNA gene libraries, which were further studied by sequencing and phylogenetic analyses. The results indicated that obvious shifts of dominant microbial populations had occurred in groundwater in response to the pollution of leachate. The closest relatives of some dominant clones are accordant with the dominating redox processes determined by hydrochemical analyses, based on the GenBank's indications on the ability to perform redox reactions.

An experimental study on effects of paraformaldehyde fixation on viscoelasticity of rat vertebrae / 医用生物力学

Objective To observe the effect of paraformaldehyde fixation on viscoelastic properties of the vertebrae in rats, so as to find the best methods of preserving cancellous bone samples from the perspective of biomechanics. Methods Twenty 8-week-old healthy female Sprague-Dawley rats were selected, and their whole L4 and L5 vertebra were separated by surgery. The total 40 vertebrae were randomly and evenly divided into experimental group and control group. The experimental group was fixed with 4% paraformaldehyde for 72 h, and the control group was transferred to 5 mL EP tube and cryopreserved at -20 ℃. Ten vertebrae were randomly selected from each group for stress relaxation and creep experiments. After 7 200 s, the samples were collected and their micro-structure changes were analyzed by micro-CT. Results The relaxation creep curve of experimental group was smoother than that of control group, the time to reach steady state was shorter, and the total amount of relaxation creep at 500 s and 7 200 s was significantly decreased (P<0.01). Micro-CT results showed that relaxation and creep experiment could cause trabecular rupture, and trabecular damage was more severe in experimental group than that in control group. Conclusions Paraformaldehyde significantly reduce the viscoelasticity of rat vertebrae, and it is more easily to cause microstructure damage under mechanical stimulation, which is detrimental to cancellous bone preservation.