Phenanthroline Derived N-Doped Carbon Dots as Robust Metal-Free Photocatalysts for PET-RAFT Polymerization and Polymerization-Induced Self-Assembly.

Metal-free organic photocatalysts for photo-mediated reversible deactivation radical polymerization (photo-RDRP) are witnessed to make increasing advancement in the precise synthesis of polymers. However, challenges still exist in the development of high-efficiency and environmentally sustainable carbon dots (CDs)-based organocatalysts. Herein, N-doped CDs derived from phenanthroline derivative (Aphen) are prepared as metal-free photocatalysts for photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. The introduction of phenanthroline structure enhances the excited state lifetime of CDs and expands the conjugated length of their internal structure to enable the light-absorption to reach green light region, thereby enhancing photocatalytic activity. The as-designed CDs exhibit unprecedented photocatalytic capacity in photopolymerization even in large-volume reaction (100 mL) with high monomer conversion and narrow polymer dispersity (Mw/Mn < 1.20) under green light. The photocatalytic system is compatible with PET-RAFT polymerization of numerous monomers and the production of high molecular weight polyacrylate (Mn >250 000) with exquisite spatiotemporal control. Above results confirm the potential of CDs as photocatalyst, which has not been achieved with other CDs catalysts used in photo-RDRP. In addition, the construction of fluorescent polymer nanoparticles using CDs as both photocatalyst and phosphor through photoinitiated polymerization-induced self-assembly (Photo-PISA) technology is successfully demonstrated for the first time.

Integrating Hybrid Perovskite Nanocrystals into Metal-Organic Framework as Efficient S-Scheme Heterojunction Photocatalyst for Synergistically Boosting Controlled Radical Photopolymerization under 980 nm NIR Light.

S-scheme heterojunction photocatalyst MAPbI3@PCN-222 with light absorption extending to the NIR region is constructed by embedding organic-inorganic hybrid perovskite (MAPbI3) into porphyrinic Zr-MOF (PCN-222). Both in situ X-ray photoelectron spectroscopy, ultraviolet photoelectron spectral characterization, and photocatalytic polymerization experiment prove the formation of S-scheme heterojunction. MAPbI3@PCN-222 with a low dosage (90 ppm) displays an impressive photocatalytic ability for 980 nm light-mediated photoinduced electron/energy-transfer-reversible addition-fragmentation chain-transfer (PET-RAFT) polymerization in air. The well-defined controllable-molecular weight polymers including block copolymers and ultrahigh-molecular weight polymers can be achieved with narrow distributions (Mw/Mn < 1.20) via rapid photopolymerization. The industrial application potential of the photocatalyst also has been proved by scale-up synthesis of polymers with low polydispersity under NIR light-induced photopolymerization in a large-volume reaction system (200 mL) with high monomer conversion up to 99%. The penetration photopolymerization through the 5 mm polytetrafluoroethylene plate and excellent photocontrollable behavior illustrate the existence of long-term photogenerated electron transfer of heterojunction and abundant free radicals in photopolymerization. The photocatalyst still retains high catalytic activity after 10 cycles of photopolymerization in air. It is revealed for the first time that the special PET-RAFT polymerization pathway is initiated by the aldehyde-bearing α-aminoalkyl radical derived from the oxidization of triethanolamine (TEOA) by the heterojunction photocatalyst. This research offers a new insight into understanding the NIR-light-activated PET-RAFT polymerization mechanism in the presence of TEOA.

Profiling microbial removal of micropollutants in sand filters: Biotransformation pathways and associated bacteria.

Although there is growing evidence that micropollutants can be microbially converted in rapid sand filters of drinking water treatment plants (DWTPs), little is known about the biotransformation pathways and associated microbial strains in this process. Here, we constructed sand filter columns filled with manganese or quartz sand obtained from full-scale DWTPs to explore the biotransformation of eight micropollutants. Under seven different empty bed contact times (EBCTs), the column experiments showed that caffeine and atenolol were easily removed (up to 92.1% and 97.6%, respectively) with adsorption and microbial biotransformation of the filters. In contrast, the removal of other six micropollutants (i.e., naproxen, carbamazepine, atrazine, trimethoprim, sulfamethoxazole, and sulfadiazine) in the filters were less than 27.1% at shorter EBCTs, but significantly increased at EBCT = 4 h, indicating the dominant role of microbial biotransformation in these micropollutants removal. Integrated analysis of metagenomic reads and transformation products of micropollutants showed a shift in caffeine oxidation and demethylation pathways at different EBCTs, simultaneous occurrence of atrazine hydrolysis and oxidation pathways, and sulfadiazine and sulfamethoxazole oxidation in the filters. Furthermore, using genome-centric analysis, we observed previously unidentified degrading strains, e.g., Piscinibacter, Hydrogenophaga, and Rubrivivax for caffeine transformation, and Methylophilus and Methyloversatilis for atenolol transformation.

Pectin in Metabolic Liver Disease.

Alterations in the composition of the gut microbiota (dysbiosis) are observed in nutritional liver diseases, including non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) and have been shown to be associated with the severity of both. Editing the composition of the microbiota by fecal microbiota transfer or by application of probiotics or prebiotics/fiber in rodent models and human proof-of-concept trials of NAFLD and ALD have demonstrated its possible contribution to reducing the progression of liver damage. In this review, we address the role of a soluble fiber, pectin, in reducing the development of liver injury in NAFLD and ALD through its impact on gut bacteria.

Alterations in the gut microbiota and metabolic profiles coincide with intestinal damage in mice with a bloodborne Candida albicans infection.

Candida albicans is an opportunistic fungus that can threaten life especially in patients with candidemia. The morbidity and mortality of candidemia originating from a central venous catheter (CVC) and illicit intravenous drug use (IVDU) are increasing. However, the mechanism underlying the bloodborne C. albicans infection remains unclear. Herein, we evaluated the gut microbiome, metabolites and intestinal mucosa by constructing the mouse models with candidemia. Model mice were injected with C. albicans via tail vein. Control mice underwent sham procedures. We observed basic life characteristics, intestinal damage-related alterations using hematoxylin and eosin (H&E) staining, intestinal tight junction protein levels, and intestinal permeability in these mice. Fecal samples were analyzed by performing 16S rRNA gene sequencing of the microbiota and LC-MS metabolomics to reveal the perturbations in intestinal flora and metabolism exacerbating intestinal damage. Weight loss, a decreased survival rate, C. albicans infection spread, and colonic epithelial damage occurred in the model group. Furthermore, the intestinal flora abundance was reduced. Several probiotics, such as Lactobacillus, and butyrate-producing bacteria, including Roseburia, Lachnospiraceae, and Clostridia, were depleted, and some pathogenic bacteria, such as Escherichia-Shigella and Proteus, belonging to the Proteobacteria phylum, and the inflammation mediators Ruminococcus and Parabacteroides were enriched in model mice. Multiple differentially altered metabolic pathways were observed and mainly related to bile acid, arachidonic acid, bile secretion, and arachidonic acid metabolism. This study illustrated the effects of a bloodborne C. albicans on the intestinal microbiota, metabolites, and intestinal barrier, which may provide new insights into tests or treatments for candidemia originating from CVC or IVDU.

Diallyl Disulfide (DADS) Ameliorates Intestinal Candida albicans Infection by Modulating the Gut microbiota and Metabolites and Providing Intestinal Protection in Mice.

Diallyl disulfide (DADS), a garlic extract also known as allicin, has been reported to have numerous biological activities, including anticancer, antifungal, and inflammation-inhibiting activities, among others. Although many studies have assessed whether DADS can treat Candida albicans infection in vitro, its in vivo function and the underlying mechanism are still not clear. Accumulated evidence has implicated the gut microbiota as an important factor in the colonization and invasion of C. albicans. Thus, this study aimed to identify the mechanism by which DADS ameliorates dextran sulfate (DSS)-induced intestinal C. albicans infection based on the systematic analysis of the gut microbiota and metabolomics in mice. Here, we determined the body weight, survival, colon length, histological score, and inflammatory cytokine levels in the serum and intestines of experimental mice. Fecal samples were collected for gut microbiota and metabolite analysis by 16S rRNA gene sequencing and LC-MS metabolomics, respectively. DADS significantly alleviated DSS-induced intestinal C. albicans infection and altered the gut microbial community structure and metabolic profile in the mice. The abundances of some pathogenic bacteria, such as Proteobacteria, Escherichia-Shigella, and Streptococcus, were notably decreased after treatment with DADS. In contrast, SCFA-producing bacteria, namely, Ruminiclostridium, Oscillibacter, and Ruminococcaceae_UCG-013, greatly increased in number. The perturbance of metabolites in infectious mice was improved by DADS, with increases in secondary bile acids, arachidonic acid, indoles and their derivatives, which were highly related to the multiple differentially altered metabolic pathways, namely, bile secretion, arachidonic acid metabolism, and tryptophan metabolism. This study indicated that DADS could modulate gut microbiota and metabolites and protect the gut barrier to alleviate DSS-induced intestinal C. albicans infection in mice. Moreover, this work might also provide novel insight into the treatment of C. albicans infection using DADS.

Metagenomics Unravels Differential Microbiome Composition and Metabolic Potential in Rapid Sand Filters Purifying Surface Water Versus Groundwater.

Designed for retaining suspended particles, rapid sand filters (RSFs) are widely used in drinking water treatment. There is increasing evidence that microbial processes within RSFs contribute to the transformation and removal of organic carbon, nitrogen, and metal pollutants. Here, we linked microbial composition and functional profiles with the treatment performance of 12 different RSFs that significantly removed influent ammonium and manganese (Mn). Metagenomic analyses showed that chemoautotrophic or methanotrophic bacteria were prevalent in the groundwater filters, and chemoheterotrophic bacteria encoding more carbohydrate- and xenobiotic-metabolizing genes were more abundant in the surface water filters. Approximately 92% of ammonium was transformed into nitrate, with a critical contribution from comammox Nitrospira. The composition of comammox amoA differed between groundwater and surface water filters, with clade A dominating groundwater filters (78.0 ± 12.0%) and clade B dominating surface water filters (91.9 ± 8.9%). Further, we identified six bacterial genera encoding known Mn(II)-oxidizing genes in the RSFs, with Pseudomonas accounting for 71.1%. These Mn(II)-oxidizing bacteria might promote Mn(II) oxidation and thus increase the removal of influent Mn. Overall, our study gave a comprehensive investigation of microbiome in RSFs and highlighted the roles of comammox and Mn(II)-oxidizing bacteria in water purification.

[Metabolic Functional Analysis of Dominant Microbial Communities in the Rapid Sand Filters for Drinking Water].

Rapid sand filter (RSF) is widely used in drinking water treatment plants. Rapid filtration is always considered a physicochemical process, but the effect of the microorganisms that attach to the filter media remain inadequately investigated. In order to understand the composition and functional characteristics of microbial communities in RSFs, influent water, effluent water, and filter materials from eleven RSFs in eight Chinese cities were sampled and analyzed. After filtration, dissolved organic carbon (DOC) showed a slight but significant removal due to the growth of heterotrophic microbes. The activity of ammonia-oxidizing microbes and nitrite-oxidizing microbes promoted a significant decrease in ammonia nitrogen (NH4+-N) and a significant increase in nitrate nitrogen (NO3--N) in water. No significant changes in total nitrogen (TN) were observed, indicating that denitrification and anammox were weak in the RSFs. The composition and function of the microbial communities of RSFs were assessed using metagenomic methods. Genera in the top 10% with respect to relative abundance (14 genera in total) were identified as the dominant genera, including the two ammonia-oxidizing bacteria Nitrospira and Nitrosomonas. Functional gene information for the dominant genera was also extracted for analysis. The dominant genera exhibited higher relative abundances of carbohydrate, nitrogen, sulfur, and xenobiotic metabolic pathways. Aeromonas had the highest relative abundance of carbohydrate metabolic genes, and Bradyrhizobium had the highest relative abundance of nitrogen, sulfur, and xenobiotics metabolic genes, indicating that these two genera play an important role in the transformation of substances in drinking water. Finally, the metabolic potential of the dominant genera on xenobiotics was evaluated, and the results showed that Bradyrhizobium, Sphingomonas, Methyloglobulus, Sphingopyxis, and Klebsiella were the key bacterial genera for the removal of micropollutants in RSFs.

Use of convertible flow cells to simulate the impacts of anthropogenic activities on river biofilm bacterial communities.

Bacterial attachment to surfaces and the development of biofilms are crucial processes during the self-purification of polluted rivers. Biofilm bacterial communities also are a potential indicator of the human impact on an aquatic system. Here, we used indoor reactors with 7.7cm3 transparent convertible flow cells to observe the formation of biofilms in river water from different land-use areas (i.e., an undisturbed mountainous area, a wastewater-discharge urban area, and a pesticide-fertilizer applied agricultural area). We then compared the bacterial biomass, composition, and function among the formed biofilms and explored whether the biofilm bacterial communities formed in polluted river water (urban area) could shift to those formed in unpolluted water (mountainous area) after simulating water-body remediation. After 60d of indoor biofilm cultivation, the biofilms formed with the three types of influent were markedly different. Anthropogenic activities (e.g., wastewater discharge and pesticide-fertilizer use) facilitated biofilm bacterial production and the metabolic rate and altered the composition and metabolic patterns of the biofilm bacterial communities. After switching from an urban water to mountainous water influent in the same reactor, the biofilm bacterial communities that initially formed in the polluted discharge did not shift to that formed in unpolluted water. This result indicated that even after water remediation, the composition of the river biofilm bacterial community would not recover to a community like that observed under non-polluted conditions. Our study highlights possible issues related to current pollution-remediation routines and emphasizes the importance of sustainable anthropogenic activities within river basins.

Integrating microbial biomass, composition and function to discern the level of anthropogenic activity in a river ecosystem.

Anthropogenic activities (e.g., wastewater discharge and pesticide and fertilizer use) have considerable impact on the biotic properties of natural aquatic ecosystems, especially the microbial community and function. Microbes can respond to anthropogenic activities and are thus potential indicators of activity levels. Several reports have documented the impacts of anthropogenic activities on the variations in the microbial community, but the direct use of microbial community indices to discern anthropogenic activity levels remains limited. Here, we integrated flow cytometry, 16S rRNA sequencing, and natural organic matter metabolism determination to investigate microbial biomass, composition, and function in three areas along a gradient of anthropogenic disturbance (less-disturbed mountainous area, wastewater-discharge urban area, and pesticide and fertilizer used agricultural area) in a river ecosystem. Multiple statistical methods were used to explore the causal relationships between changes in environmental factors and microbial variation. Results showed that anthropogenic activities (e.g., wastewater discharge, pesticide and fertilizer use) facilitated bacterial production, affected dominant species distribution, and accelerated natural organic matter (NOM) metabolic rate by microbes. After screening the possible factors influencing the microbial community, we determined that cyanobacterial concentration could be a diagnostic indicator of nutrient levels. We also developed a NOM metabolic index to quantitatively reflect the holistic influence of nutrients and xenobiotics.