High-level production of poly-γ-glutamic acid by a newly isolated Bacillus sp. YJY-8 and potential use in increasing the production of tomato.

Strain YJY-8, a new γ-polyglutamic acid producer, was separated from fermented soybean paste samples. The strain was identified as a genus of Bacillus by morphological and 16S rDNA sequence analysis and was named Bacillus sp. YJY-8. The optimal medium composition and cultural conditions were studied using a single-factor experiment and a response surface experiment. The optimized medium consisted of monosodium glutamate 70 g/L, glucose 54.3 g/L, glycerol 31.8 g/L, ammonium sulfate 11.1 g/L, yeast extract 3.2 g/L, tryptone 1.5 g/L, L-glutamic acid 6.8 g/L, MgSO4 7H2O 0.5 g/L, FeCl3 6H2O 0.02 g/L, KH2PO4 0.9 g/L, CaCl2 0.03 g/L, MnSO4 H2O 0.3 g/L, ammonium molybdate 0.02 g/L, pH 7.0. The optimal cultivation conditions were 35 °C and pH 7.0. Under the optimized conditions, after 48 hr of cultivation, the highest shaking flask fermentation level of γ-PGA reached 65.2 ± 0.36 g/L. In addition, through fed-batch fermentation in 30 L fermenters, the fermentation level of γ-PGA reached its highest level at 88.42 g/L and productivity was 1.23 g/(L hr) after 72 hr. Then, the effect of γ-PGA on tomato yield was investigated. At the seedling stage, the plant height and stem diameter of γ-PGA treated plants increased by 5.69 and 15.735% after spraying γ-PGA for 19 days. During the flowering and fruiting period, the stem diameter of the γ-PGA treatment group increased by 6.74%, with a maximum increase of 11.65%. The number of fruit branches increased by 0.56-16.29% and the number of fruit sets increased by 1.01-28.47%. At the fruit maturation stage, the yield of tomatoes increased by 10.51, 14.27, and 5.83%.

Impacts of COVID-19 on tourists' destination preferences: Evidence from China.

Using data of online ticket sales for attractions in the seven provinces of South Central China, this study focuses on the impact of COVID-19 on tourists' destination preferences after the end of lockdown. Empirical results reveal that tourists' destination preferences have changed significantly, which holds under a number of robustness checks. Specifically, we find that tourists avoid traveling to destinations with more confirmed cases of COVID-19 relative to their places of origin, especially Hubei Province, and prefer destinations close to home, especially local attractions. The empirical findings have significant implications for managers and policymakers in tourism and we provide potential mechanisms for these findings based on signaling, risk perception, and prospect theory.

Association Between Serum Vitamin A Levels and Recurrent Respiratory Tract Infections in Children.

To evaluate the association between serum vitamin A levels and the prevalence of recurrent respiratory tract infections (RRTIs) in children and adolescents and to provide evidence that would help decrease the prevalence of respiratory tract infections (RTIs) in children. This cross-sectional study included 8034 children and adolescents in Beijing aged 6 months to 17 years. RRTI and RTI symptoms were diagnosed according to the Clinical Concept and Management of Recurrent Respiratory Tract Infections in Children. Multivariate logistic regression models were used to evaluate the association between serum vitamin A levels and RRTIs after adjusting for potential confounders. Among the included children, 721 (8.97%) were diagnosed with vitamin A deficiency, whereas 3,073 (38.25%) were diagnosed with subclinical vitamin A deficiency. Only 28.8% (208/721) of children with vitamin A deficiency and 53.1% (1,631/3,073) of children with subclinical vitamin A deficiency had no RRTI and RTI symptoms, respectively. Compared with children with normal vitamin A levels, those with vitamin A deficiency and subclinical vitamin A deficiency had a greater risk for RRTIs, with an odds ratio (OR) of 6.924 [95% confidence interval (CI): 5.433-8.824] and 2.140 (95% CI: 1.825-2.510), respectively]. Vitamin A levels were also positively associated with RTI symptoms, with those having vitamin A deficiency and subclinical vitamin A deficiency showing an OR of 1.126 (95% CI: 0.773-1.640) and 1.216 (95% CI: 1.036-1.427), respectively. The present cross-sectional study found that low serum vitamin A levels were significantly associated with RRTI or RTI prevalence in children and adolescents.

Synthesis and optical properties of Eu3+ doped ZnO nanoparticles used for white light emitting diodes.

ZnO nanoparticles doped with trivalent europium ions (Eu3+) were synthesized by the hydrothermal method. The structural properties of the samples were investigated by the X-ray diffraction (XRD). The results indicated that Eu3+ was incorporated into the lattice of ZnO. Photoluminescence (PL) measurements of ZnO:Eu3+ showed a strong red luminescence emission. Specially, the red emission can be obtained even under the nonresonant excitation of 320 nm, and it is explained by an energy transfer mechanism in which the energy is transferred from ZnO matrix to Eu3+. These results indicate that the ZnO:Eu3+ is the attractive candidate phosphor for the application in phosphor-converted light-emitting diodes (pc-LEDs) as red phosphor. The intensity of Eu3+ PL decreased with the increasing Eu3+ concentration and the concentration quenching mechanism was presented based on non-radiative recombination processes in ZnO and the energy back-transfer from the excited state of Eu3+ to the ZnO host. Moreover, the samples were synthesized under low temperature condition.