Effects of cadmium and flooding on the formation of iron plaques, the rhizosphere bacterial community structure, and root exudates in Kandelia obovata seedlings.

In the rhizosphere, plant root exudates (REs) serve as a bridge between plant and soil functional microorganisms, which play a key role in the redox cycle of iron (Fe). This study examined the effects of periodic flooding and cadmium (Cd) on plant REs, the rhizosphere bacterial community structure, and the formation of root Fe plaques in the typical mangrove plant Kandelia obovata, as well as the relationship between REs and Fe redox cycling bacteria. Based on two-way analysis of variance, flooding and Cd had a considerable effect on the REs of K. obovata. DOC, NH4+-N, NO3--N, dissolved inorganic phosphorus, acetic acid, and malonic acid concentrations in REs of K. obovata increased considerably with the increase of Cd concentration under 5 and 10 h flooding conditions. Fe plaque development in the plant root was stimulated by flooding and Cd, although flooding was more effective. After Cd treatment, the ways in which Fe-oxidizing bacteria (FeOB) and Fe-reducing bacteria (FeRB) were enriched in the rhizosphere and rhizoplane of plants were different. Thiobacillus and Sideroxydans (dominant FeOB) were more abundant in the plant rhizosphere, whereas Acinetobacter (dominant FeRB) was more abundant in the rhizoplane. Cd considerably decreased the relative abundance of unclassified_f_Gallionellaceae in the rhizosphere and rhizoplane but dramatically enhanced the relative abundance of Thiobacillus, Shewanella, and unclassified_f_Geobacteraceae. Unclassified_f_Geobacteraceae and Thiobacillus exhibited substantial positive correlations with citric acid and DOC in REs in the rhizosphere and rhizoplane but strong negative correlations with Sideroxydans. The findings indicate that Cd and flooding treatments may play a role in the production and breakdown of Fe plaque in K. obovata roots by affecting the relative abundance of Fe redox cycling bacteria in the rhizosphere and rhizoplane.

Effects of exogenous organic acids and flooding on root exudates, rhizosphere bacterial community structure, and iron plaque formation in Kandelia obovata seedlings.

The rhizosphere of coastal wetland plants is the active interface of iron (Fe) redox transformation. However, coupling mechanism between organic acids (OAs) exuded by plant roots and Fe speciation transformation participated by Fe redox cycling bacteria in the rhizosphere is still unclear. Effects of four common OAs (citric acid, malic acid, tartaric acid, and oxalic acid) on root exudation, rhizosphere bacterial community structure, root Fe plaque, and Fe redox cycling bacterial communities of Kandelia obovata were investigated in this study. Long-term flooding (10 h) was conducive to K. obovata seedlings exuding additional dissolved organic carbon (DOC) and nitrogen and phosphorus organic matter (NH4+-N, NO3--N, and dissolved inorganic phosphorus [DIP]) under each OA level. DOC, NH4+-N, NO3--N, and DIP in root exudates increased significantly with the increase of exogenous OA level. Notably, long flooding time corresponds to an evidently increasing trend. Exogenous OAs also significantly increased contents of formic and oxalic acids in root exudates. Exogenous OAs and flooding enhanced the rhizosphere effect of K. obovata and significantly enhanced bacterial diversity of the rhizosphere and relative abundance of dominant bacteria in rhizoplane. Bacterial diversity in the rhizosphere of K. obovata seedlings was significantly higher than that in the rhizoplane under the same level of OAs and flooding. Fe plaque content of K. obovata root decreased significantly and the relative abundance of typical Fe-oxidizing bacteria, such as Gallionella, unclassified_f__Gallionellaceae, and Sideroxydans, decreased significantly in the rhizosphere but increased significantly in the rhizoplane with the increase of the treatment level of exogenous OAs. This finding is likely due to the Fe3+ reduction caused by acidification of rhizosphere environment after exogenous OA treatment rather than the result of chemotactic colonization of Fe redox cycling bacteria in the rhizoplane.

Utilization of neurosurgical perioperative antimicrobial prophylaxis in a Chinese teaching hospital.

Background Audits of antimicrobial prophylaxis is an essential strategy to identify practice gaps in antimicrobial prescribing in healthcare facilities. There is a lack of studies on the costs, quality, and antimicrobial use density of neurosurgical perioperative antimicrobial prophylaxis in China. Objectives Evaluate the appropriateness of perioperative antimicrobial prophylaxis in neurosurgeries and analyze the costs, quality, and antimicrobial use density of neurosurgical perioperative antimicrobial prophylaxis. Setting Beijing Tsinghua Changgung Hospital, a teaching hospital in Beijing. Methods This retrospective study was conducted among 262 neurosurgical patients without infections during 2017. The appropriateness of perioperative antimicrobial prophylaxis was determined based on relevant international and Chinese perioperative antimicrobial prophylaxis guidelines. Main outcome measures Discrepancy rates in perioperative antimicrobial prophylaxis, including indication, choice of antimicrobials, dose, route of administration, time of administration of the first dose, re-dosing, and duration, were analyzed. Results Discrepancies were observed between current practice and relevant guidelines. A total of 51 (32.1%) procedures failed to administer intraoperative re-dosing as needed, and the perioperative antimicrobial prophylaxis duration of 217 (82.8%) procedures was inappropriately prolonged. The choice of antimicrobial agents was optimal in 249 (95%) procedures, and the timing of perioperative antimicrobial prophylaxis was appropriate in all procedures. If perioperative antimicrobial prophylaxis was implemented according to guidelines, the defined daily dose per 100 procedures would decrease from 31.97 to 16.99, and the total cost would reduce from $2000 to $490. Conclusions Effective antimicrobial stewardship is urgently needed to promote the appropriateness of neurosurgical perioperative antimicrobial prophylaxis in China.

Self-Supported Ternary Ni-S-Se Nanorod Arrays as Highly Active Electrocatalyst for Hydrogen Generation in Both Acidic and Basic Media: Experimental Investigation and DFT Calculation.

In this study, a novel three-dimensional self-supported ternary NiS-Ni9S8-NiSe nanorod (NR) array cathode has been successfully in situ constructed by a two-step hydrothermal route. When applied to hydrogen evolution, the synthesized NiS-Ni9S8-NiSe-NR electrode demonstrates optimized electrocatalytic activity and long-term durability, only requiring overpotentials as low as 120 and 112 mV to drive 10 mA cm-2 for hydrogen evolution reaction in 0.5 M H2SO4 and 1.0 M KOH, respectively. Density functional theory calculation reveals that after Se doping Se 3d orbitals are bonded to Ni 3d orbitals and S p orbitals near Fermi level, attesting a significant electron transfer between nickel and selenium atoms. The success of enhancing the electrocatalytic performance via introducing the Se dopant holds great promise for the potential optimization of other transition-metal compounds in highly efficient electrochemical water splitting for large-scale hydrogen production.

A nanocluster-based fluorescent sensor for sensitive hemoglobin detection.

In this report, a fluorescence sensor for sensitive detection of hemoglobin was developed. Gold nanoclusters were first synthesized with bovine serum albumin. It was found that both hydrogen peroxide and hemoglobin could weakly quench the fluorescence from the gold nanoclusters, but when these two were applied onto the nanolcusters simultaneously, a much improved quenching was resulted. This enhancing effect was proved to come from the catalytic generation of hydroxyl radical by hemoglobin. Under an optimized condition, the quenching linearly related to the concentration of hemoglobin in the range of 1-250nM, and a limit of detection as low as 0.36nM could be obtained. This provided a sensitive means for the quantification of Hb. The sensor was then successfully applied for blood analyses with simple sample pretreatment.

Turn-on fluorescence detection of ascorbic acid with gold nanolcusters.

In this report, a sensitive fluorescent detection of ascorbic acid was developed with protein-stabilized gold nanoclusters. The fluorescence signal from the gold nanoclusters could be effectively quenched by elemental iodine. This kind of quenching could be inhibited by ascorbic acid through a corresponding reduction process, thus a turn-on response toward ascorbic acid was obtained. The validity and performances of the detection scheme were evaluated. The fluorescence responses were linearly related to ascorbic acid in the concentration range 0.1-10µM, and the method was capable of detecting ascorbic acid down to 22nM. The high performances of the developed scheme greatly simplified the sample preparation step, and the method was successfully applied for real sample analyses.