Iron oxide nanozymes stabilize stannous fluoride for targeted biofilm killing and synergistic oral disease prevention.

Dental caries (tooth decay) is the most prevalent human disease caused by oral biofilms, affecting nearly half of the global population despite increased use of fluoride, the mainstay anticaries (tooth-enamel protective) agent. Recently, an FDA-approved iron oxide nanozyme formulation (ferumoxytol, Fer) has been shown to disrupt caries-causing biofilms with high specificity via catalytic activation of hydrogen peroxide, but it is incapable of interfering with enamel acid demineralization. Here, we find notable synergy when Fer is combined with stannous fluoride (SnF 2 ), markedly inhibiting both biofilm accumulation and enamel damage more effectively than either alone. Unexpectedly, our data show that SnF 2 enhances the catalytic activity of Fer, significantly increasing reactive oxygen species (ROS) generation and antibiofilm activity. We discover that the stability of SnF 2 (unstable in water) is markedly enhanced when mixed with Fer in aqueous solutions without any additives. Further analyses reveal that Sn 2+ is bound by carboxylate groups in the carboxymethyl-dextran coating of Fer, thus stabilizing SnF 2 and boosting the catalytic activity. Notably, Fer in combination with SnF 2 is exceptionally effective in controlling dental caries in vivo , preventing enamel demineralization and cavitation altogether without adverse effects on the host tissues or causing changes in the oral microbiome diversity. The efficacy of SnF 2 is also enhanced when combined with Fer, showing comparable therapeutic effects at four times lower fluoride concentration. Enamel ultrastructure examination shows that fluoride, iron, and tin are detected in the outer layers of the enamel forming a polyion-rich film, indicating co-delivery onto the tooth surface. Overall, our results reveal a unique therapeutic synergism using approved agents that target complementary biological and physicochemical traits, while providing facile SnF 2 stabilization, to prevent a widespread oral disease more effectively with reduced fluoride exposure.

Spatial and seasonal change in algal community structure and its interaction with nutrient dynamics in a gravel-bed urban river.

Harmful algal blooms frequently occur in urban rivers due to intense human activities. However, little is known about the change in algal community structure and its interactions with nutrient dynamics in gravel-bed urban rivers. In present study, water samples were collected from a gravel-bed River Xin'an, China for five months over four seasons and a rainy month to measure algal community structure, dissolved nitrogen gas (N2) and Argon (Ar) concentrations, and other water quality parameters. The results showed that the harmful Cyanophyta accounted for 31.6 ± 24.1% of the total community in the hot season while Bacillariophyta contributed more than 60% to the community in the other three seasons. The N2 was supersaturated in the moderate and cold seasons but it was unsaturated in the hot season, along with high concentrations of nitrogen-fixing cyanobacteria (Anabaena), indicating that the nitrogen fixation capacity was strong and even stronger than denitrification and anammox in the hot season. However, nitrogen fixation was not the main source of nitrogen in the water column. The concentrations of nutrients and Chla in the downstream river were significantly higher than those in the upstream river (p < 0.001 for nutrients and p = 0.029 for Chla), suggesting that human activities along the river greatly affected nutrient concentrations, as well as algal growth. Our study provides new insights into the algal community succession in a gravel-bed urban river and puts forward effective measures such as controlling exogenous nutrient input and dredging organic sediment for mitigating the harmful algal blooms in urban rivers.

New insights into eutrophication management: Importance of temperature and water residence time.

Eutrophication and harmful cyanobacterial blooms threaten water resources all over the world. There is a great controversy about controlling only phosphorus or controlling both nitrogen and phosphorus in the management of lake eutrophication. The primary argument against the dual nutrients control of eutrophication is that nitrogen fixation can compensate the nitrogen deficits. Thus, it is of great necessary to study the factors that can significantly affect the nitrogen fixation. Due to the difference of climate and human influence, the water quality of different lakes (such as water temperature, N:P ratio and water residence time) is also quite different. Numerous studies have reported that the low N:P ratio can intensify the nitrogen fixation capacities. However, the effects of temperature and water residence time on the nitrogen fixation remain unclear. Thus, 30 shallows freshwater lakes in the eastern plain of China were selected to measure dissolved N2 and Ar concentrations through N2: Ar method using a membrane inlet mass spectrometer to quantify the nitrogen fixation capacities and investigate whether the temperature and water residence time have a great impact on nitrogen fixation. The results have shown that the short lake water residence time can severely inhibit the nitrogen fixation capacities through inhibiting the growth of nitrogen-fixing cyanobacteria, changing the N:P ratio and resuspending the solids from sediments. Similarly, lakes with low water temperature also have a low nitrogen fixation capacity, suggesting that controlling nitrogen in such lakes is feasible if the growth of cyanobacteria is limited by nitrogen.

Cellular Uptake of Few-Layered Black Phosphorus and the Toxicity to an Aquatic Unicellular Organism.

With the potential continuous application of mono- or few-layered black phosphorus (BP) in electronic, photonic, therapeutic, and environmental fields, the possible side effects of BP on aquatic organisms after release into natural water are of great concern. We investigated the potential toxicity of BP on the unicellular organism, Tetrahymena thermophila. After the exposure for 8 h at 10 µg/mL, the reproduction of T. thermophila significantly decreased by 46.3%. Severe cell membrane and cilium damage were observed by scanning electron microscopy (SEM) upon treatment with BP. Based on bright-field microscopy and three-dimensional Raman imaging, we investigated the cellular uptake and translocation of BP within T. thermophila. It was observed that the engulfment of BP by T. thermophila was oral apparatus dependent, through which intracellular BP was then transported to the posterior end of T. thermophila by food vacuole packaging. Our study also revealed that BP induced the increase of intracellular reactive oxidant species and formed oxidative stress-dependent toxicity to T. thermophila. Our findings paved a way for better understanding the BP toxicityon aquatic organisms and its potential ecological risks.

Inhibition effect of Zedoary turmeric oil on Listeria monocytogenes and Staphylococcus aureus growth and exotoxin proteins production.

PURPOSE: Zedoary turmeric oil (ZTO), the steam extract of Curcuma zedoaria Rosc was researched for its chemical composition, antibacterial activity, and mechanism for countering two major food-borne pathogenic species, Listeria monocytogenes and Staphylococcus aureus. METHODOLOGY: Gas chromatography-mass spectrometry (GC-MS) was used to analyse and characterize the chemical composition of ZTO. Its MICs for the two bacterial species and growth curves were measured. Western blot and real-time reverse-transcription (RT)-PCR assays were utilized to elaborate the mechanism of the antibacterial effect of ZTO by examining the expression levels of virulence-related extracellular proteins. ELISA was used to explore the biological relevance. RESULTS: GC-MS revealed high contents of curzerene, eucalyptol, germacrone and (-)-g-elemene representing 28.45, 10.94, 10.77 and 10.54  %, respectively, of the whole components. The MICs of ZTO that combatted L. monocytogenes and S. aureus were similar (1-2 mg ml-1 ). After adding ZTO at increasing concentrations, there was an evident reduction in the transcription of hly, iap, hla, sea, seb and agrA in a dose-dependent manner. Furthermore, TNF-α accumulation in RAW264.7 cells stimulated by L. monocytogenes and S. aureus supernatants was restricted by a 1/4 MIC of ZTO. CONCLUSION: Overall, L. monocytogenes and S. aureus were comparably susceptible to ZTO. These data demonstrated that ZTO's antimicrobial property was mediated by the repression of the production of virulence factors involved in L. monocytogenes and S. aureus pathogenesis, a finding that can potentially further progress in the development of new anti-virulence drugs.

Antimicrobial potential of myristic acid against Listeria monocytogenes in milk.

Listeria monocytogenes (L. monocytogenes), an important food-borne pathogenic microorganism, has resistance immune function to many commonly used drugs. Myristic acid is a traditional Chinese herbal medicine, but it has been rarely used as a food additive, limiting the development of natural food preservatives. In this study, the antibacterial activity and mechanism of myristic acid against L. monocytogenes were studied. The minimum inhibitory concentration (MIC) of myristic acid against 13 L. monocytogenes strains ranged from 64 to 256 µg ml-1. The time-kill assay demonstrated that when myristic acid was added to dairy products, flow cytometry confirmed that myristic acid influenced cell death and inhibited the growth of L. monocytogenes. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and NPN uptake studies illustrated that myristic acid changed the bacterial morphology and membrane structure of L. monocytogenes, which led to rapid cell death. Myristic acid could bind to DNA and lead to changes in DNA conformation and structure, as identified by fluorescence spectroscopy. Our studies provide additional evidence to support myristic acid being used as a natural antibacterial agent and also further fundamental understanding of the modes of antibacterial action.

Phenotype and RNA-seq-Based transcriptome profiling of Staphylococcus aureus biofilms in response to tea tree oil.

Staphylococcus aureus (S. aureus) is a Gram-positive bacterium that causes a wide range of diseases, including food poisoning. Tea tree oil (TTO), an essential oil distilled from Melaleuca alternifolia, is well-known for its antibacterial activities. TTO effectively inhibited all 19 tested strains of S. aureus biofilm and planktonic cells. Phenotype analyses of S. aureus biofilm cells exposed to TTO were performed by biofilm adhesion assays, eDNA detection and PIA release. RNA sequencing (RNA-seq) was used in our study to elucidate the mechanism of TTO as a potential antibacterial agent to evaluate differentially expressed genes (DEGs) and the functional network in S. aureus ATCC 29213 biofilms. TTO significantly changed (greater than a 2- or less than a 2-fold change) the expression of 304 genes in S. aureus contained in biofilms. The levels of genes related to the glycine, serine and threonine metabolism pathway, purine metabolism pathway, pyrimidine metabolism pathway and amino acid biosynthesis pathway were dramatically changed in the biofilm exposed to TTO. Furthermore, the expression changes identified by RNA-seq analysis were verified by real-time RT-PCR. To the best of our knowledge, this research is the first study to report the phenotype and expression profiles of S. aureus in biofilms exposed to TTO.

Composition and stability of anthocyanins from purple Solanum tuberosum and their protective influence on Cr(VI) targeted to bovine serum albumin.

Anthocyanins from the purple Solanum tuberosum newly cultivated by the Taian Academy of Agricultural Sciences were extracted and analyzed using high-performance liquid chromatography (HPLC) and UV-vis spectroscopy. Four individual anthocyanins were detected as the major components, and the total anthocyanin content was 273.5 ± 14.3 mg of cyanidin-3-glucoside equiv/100 g of dry seeds. Results of color stability showed that the purple S. tuberosum anthocyanins (PSTAs) are more stable under low pH and temperatures. Heat and general food additives have fine compatibility with PSTAs; however, they are very sensitive with oxidant and reduction. The influence of PSTAs on Cr(VI) targeted to bovine serum albumin (BSA) was also studied. The quenching of BSA fluorescence caused by Cr(VI) could be delayed by PSTAs. UV-vis and circular dichroism (CD) data suggested that PSTAs can protect the secondary and tertiary structures of BSA by probably interacting with Cr(VI) in advance.