Effects of soil properties, heavy metals, and PBDEs on microbial community of e-waste contaminated soil

Heavy metals and polybrominated diphenyl ethers (PBDEs) are ubiquitous pollutants at electronic waste (e-waste) contaminated sites, their individual impacts on soil microbial community has attracted wide attention, however, limited research is available on the combined effects of heavy metals and PBDEs on microbial community of e-waste contaminated. Therefore, combined effects of heavy metals and PBDEs on the microbial community in the e-waste contaminated soil were investigated in this study. Samples were collected from Ziya e-waste recycling area in Tianjin, northern China, and the soil microbial communities were then analyzed by the high-throughput MiSeq 16S rRNA sequencing to assess the effects of soil properties, heavy metals, and PBDEs on the soil microbial community. Candidatus Nitrososphaera, Steroidobacter and Kaistobacter were the dominant microbial species in the soils. Similar microbial metabolic functions, including amino acid metabolism, carbohydrate metabolism and membrane transport, were found in all soil samples. Redundancy analysis and variation partition analysis revealed that the microbial community was mainly influenced by PBDEs (including BDE 183, BDE 99, BDE 100 and BDE 154) in horizontal soil samples. However, TN, biomass, BDE 100, BDE 99 and BDE 66 were the major drivers shaping the microbial community in vertical soil samples.

Absence of Quantum-Confined Stark Effect in GaN Quantum Disks Embedded in (Al,Ga)N Nanowires Grown by Molecular Beam Epitaxy

Several of the key issues of planar (Al,Ga)N-based deep-ultraviolet light-emitting diodes could potentially be overcome by utilizing nanowire heterostructures, exhibiting high structural perfection, and improved light extraction. Here, we study the spontaneous emission of GaN/(Al,Ga)N nanowire ensembles grown on Si(111) by plasma-assisted molecular beam epitaxy. The nanowires contain single GaN quantum disks embedded in long (Al,Ga)N nanowire segments essential for efficient light extraction. These quantum disks are found to exhibit intense light emission at unexpectedly high energies, namely, significantly above the GaN bandgap, and almost independent of the disk thickness. An in-depth investigation of the actual structure and composition of the nanowires reveals a spontaneously formed Al gradient both along and across the nanowire, resulting in a complex core/shell structure with an Al-deficient core and an Al-rich shell with continuously varying Al content along the entire length of the (Al,Ga)N segment. This compositional change along the nanowire growth axis induces a polarization doping of the shell that results in a degenerate electron gas in the disk, thus screening the built-in electric fields. The high carrier density not only results in the unexpectedly high transition energies but also in radiative lifetimes depending only weakly on temperature, leading to a comparatively high internal quantum efficiency of the GaN quantum disks up to room temperature.

Biogeography and Diversity of Freshwater Bacteria on a River Catchment Scale

To illustrate how freshwater bacterial community changes with geographic gradient, we investigated the spatial changes of bacterial abundance and community structures from over 200 samples on a catchment scale in the Songhua River using heterotrophic plate counts, flow cytometry, denaturing gradient gel electrophoresis, and pyrosequencing analysis. The results showed that the mainstream had higher cultivable bacteria and total bacterial concentration than tributaries in the Songhua River catchment. Response model analysis demonstrated that the bacterial community exhibits a biogeographical signature even in an interconnected river network system, and the total bacterial concentration and biodiversity were significantly correlated to latitude (p < 0.001) and longitude (p < 0.001). Multivariate redundancy analysis indicated that temperature was the most important factor driving bacterial community structure in the Songhua River, which accounts for 35.30% variance of communities, then dissolved oxygen (17.60%), latitude (17.60%), longitude (11.80%), and pH (5.88%). High-throughput pyrosequencing revealed that at the phylum level, Proteobacteria was numerically dominant (89.6%) in river catchment, followed by Bacteroidetes (8.1%) and Cyanobacteria (1.2%). The overall results revealed that the bacterial community was driven by geographical distance regardless of the continuum of the river on a catchment scale.

Structural and Functional Changes of Groundwater Bacterial Community During Temperature and pH Disturbances

In this study, we report the characteristics of a microbial community in sampled groundwater and elucidate the effects of temperature and pH disturbances on bacterial structure and nitrogen-cycling functions. The predominant phyla of candidate OD1, candidate OP3, and Proteobacteria represented more than half of the total bacteria, which clearly manifested as a "low nucleic acid content (LNA) bacteria majority" type via flow cytometric fingerprint. The results showed that LNA bacteria were more tolerant to rapid changes in temperature and pH, compared to high nucleic acid content (HNA) bacteria. A continuous temperature increase test demonstrated that the LNA bacterial group was less competitive than the HNA bacterial group in terms of maintaining their cell intactness and growth potential. In contrast, the percentage of intact LNA bacteria was maintained at nearly 70% with pH decrease, despite a 50% decrease in total intact cells. Next-generation sequencing results revealed strong resistance and growth potential of phylum Proteobacteria when the temperature increased or the pH decreased in groundwater, especially for subclasses α-, β-, and γ-Proteobacteria. In addition, relative abundance of nitrogen-related functional genes by qPCR showed no difference in nitrifiers or denitrifiers within 0.45 μm-captured and 0.45 μm-filterable bacteria due to phylogenetic diversity. One exception was the monophyletic anammox bacteria that belong to the phylum Planctomycetes, which were mostly captured on a 0.45-μm filter. Furthermore, we showed that both temperature increase and pH decrease could enhance the denitrification potential, whereas the nitrification and anammox potentials were weakened.

Impact of planktonic low nucleic acid-content bacteria to bacterial community structure and associated ecological functions in a shallow lake

In this study, 0.45 μm filtration, flow cytometric fingerprint, 16S rRNA amplicon sequencing, and bioinformation tools were adopted to analyze the structural diversity and potential functions of planktonic low nucleic acid (LNA)- content bacteria in a shallow lake. Three bacterial groups, namely, "LNA," "high nucleic acid (HNA)-Small," and "HNA-Large," were classified through flow cytometric fingerprint, among which the "HNA-Small" group was possibly in the proliferation stage of the "LNA" group. Total nitrogen and phosphate were the key factors that influence the growth of LNA bacteria. Results of 16S rRNA amplicon sequencing showed that LNA bacteria were phylogenetically less diverse than HNA bacteria, and Actinobacteria and Proteobacteria (especially Gamma-Proteobacteria) were the dominant phyla in LNA bacterial operational taxonomic units (OTUs). Accordingly, hgcI_clade and Pseudomonas were the most abundant bacterial genera in LNA bacterial OTUs. The fraction of low-abundance LNA bacteria was sensitive to several environmental factors, indicating that environmental factors only determined the fraction distribution of low-abundance bacteria. The prediction of metabolic and ecological functions showed that LNA and HNA bacteria had distinct metabolic and ecological functions, which were mainly attributed to the dominant and exclusive bacterial groups.

Interfacial reactions during the molecular beam epitaxy of GaN nanowires on Ti/Al2O3

We investigate the occurrence of interfacial reactions during the self-assembled formation of GaN nanowires on Ti/Al₂O₃(0001) substrates in plasma-assisted molecular beam epitaxy. The conditions typical for the synthesis of ensembles of long nanowires (>1 μm) are found to promote several chemical reactions. In particular, the high substrate temperature leads to the interdiffusion of Al and O at the Ti/Al₂O₃ interface resulting in the formation of Al _x Ti _y O_1-x-y and Ti _x O_1-x compounds. Furthermore, O is found to incorporate into the nanowires degrading their luminescence by heavy n-type doping. At the same time, impinging Ga and N species react with the substrate giving rise to the simultaneous formation of single-crystalline TiN and Ga _x Ti _y O_1-x-y compounds. The latter compounds tend to form hillocks at the substrate surface, on top of which nanowires elongate with large tilt angles with respect to the substrate normal. We develop here a specific process in order to mitigate the detrimental effects of these interfacial reactions, while maintaining the low areal density and absence of coalescence which is the strong asset of growing nanowires on Ti/Al₂O₃. We find that the combination of a thick Ti film with an intentional low temperature nitridation step preceding nanowire growth and a limited growth temperature results in ensembles of uncoalesced and well-oriented nanowires with luminescence properties comparable to those of standard GaN nanowires prepared on Si. All these properties, together with the inherent benefits of integrating semiconductors on metals, make the present materials combination a promising platform for the further development of group-III nitride nanowire-based devices.

Resistance and resilience of representative low nucleic acid-content bacteria to free chlorine exposure

Two representative low nucleic acid-content (LNA) bacterial strains, Polynucleobacter sp. CB and Sphingopyxis sp. 15Y-HN, and two commonly used microbial indicators of drinking water disinfection efficiency, Escherichia coli and Pseudomonas aeruginosa, were used to investigate the effects of chlorine disinfection. LNA bacteria were found to be more tolerant than microbial indicator strains at the same free chlorine concentrations in batch experiments. Three-stage chlorination experiments were carried out for two strains (15Y-HN and E. coli K12) to compare their responses to long-term chlorine exposure. Results from the first stage (increasing chlorine exposure from 0.0 to 0.6 mg/L and 1.2 mg/L for strain K12 and strain 15Y-HN, respectively) showed the rate constants of 99% cell damage were 10-fold lower for strain 15Y-HN than for strain K12. A second regrowth stage at low free chlorine concentrations (<0.3 mg/L for 140 h) facilitated the regrowth of chlorine-resistant populations of strains 15Y-HN and K12 in the presence of assimilable organic carbon (AOC). In the third stage, during which bacteria were exposed to increasing chlorine from 0.0 to 0.5-0.6 mg/L, strain 15Y-HN was maintained at 80% and 10⁵ cells/mL of intact cells whereas strain K12 was completely damaged. The overall results demonstrated that representative LNA bacteria exhibit strong resistance and resilience to chlorine under low AOC conditions, which should be taken into consideration in disinfection processes.

[The analysis of the effect of psycho-intervention combined with diazepam on patients with sudden sensorineural hearing loss and anxiety]

Objective: To investigate the therapeutic effect of psychological intervention combined with diazepam on sudden hearing loss patients with anxiety. Method: 108 cases of sudden hearing loss patients with anxiety were randomly divided into two groups(n=54 in each group): The control group received routine treatment of sudden hearing loss, the study group was given psychological intervention combined with diazepam tablets(2.5 mg once, twice a day) based on the routine treatment. The hearing and HAMA and SAS scores were reviewed after 10 days of treatment. Result: After 10 days of treatment, the average hearing threshold of patients in the control group and the study group were respectively increased by （19.65±7.89）dB and （26.93±9.04）dB (t=4.54, P=0.006), the HAMA score of two groups were respectively decreased by 4.68 and 10.75（t=9.949, P=0.000）and the SAS score of two groups were respectively decreased by 15.93 and 23.39 (t=6.773, P=0.000), and the total efficiency of hearing of two groups were 61.11% and 77.78% (χ²=4.441, P=0.035),respectively. the differences were statistically significant. Conclusion: Psychological intervention combined with diazepam can relieve anxiety in patients with sudden hearing loss effectively, and play a positive role in the development and prognosis of patients with sudden sensorineural hearing loss.