A set S of vertices in G is a semitotal dominating set of G if it is a dominating set of G and every vertex in S is within distance 2 of another vertex of S . The semitotal domination number , γ t 2 ...( G ), is the minimum cardinality of a semitotal dominating set of G . Clearly, γ ( G ) ≤ γ t 2 ( G ) ≤ γ t ( G ). In this paper, for any nontrivial tree T that is not a star, we investigate the ratios γ t 2 ( T )/ γ ( T ) and γ t ( T )/ γ t 2 ( T ), and provide constructive characterizations of trees achieving the upper bounds.
•Double-edged sword effects of DNRA bacteria on anammox performance were studied.•Overgrowth DNRA bacteria out competed anammox cell with toxic NO2−-N accumulation.•Predominant C. Kuenenia were ...replaced by C. Brocadia with high NO2−-N loading.•DNRA showed positive effects on anammox with low RatioNH4+-N: NO2−-N (1.25).
Dissimilatory nitrate reduction to ammonium (DNRA) bacteria imposing double-edged sword effects on anammox bacteria were investigated in an anammox-membrane bioreactor (MBR) experiencing an induced crash-recovery event. During the experiment, the anammox-MBR was loaded with NH4+-N:NO2−-N ratios (RatioNH4+-N: NO2−-N) of 1.20–1.60. Initially, the anammox-MBR removed over 95% of 100 mg/L NH4+-N and 132 mg/L NO2−-N (RatioNH4+-N: NO2−-N = 0.76, the well accepted stoichiometric RatioNH4+-N: NO2−-N for anammox) in the influent (Stage 0). Then, we induced a system crash-recovery event via nitrite shock loadings to better understand responses from different guilds of bacteria in anammox-MBR, loaded with 1.60 RatioNH4+-N: NO2−-N with 100 mg/L NO2−-N in the influent (Stage 1). Interestingly, the nitrogen removal by anammox bacteria was maintained for about 20 days before starting to decrease significantly. In Stage 2, we further increased influent nitrite concentration to 120 mg/L (1.33 RatioNH4+-N: NO2−-N) to simulate a high nitrite toxicity scenario for a short period of time. As expected, nitrogen removal efficiency dropped to only 16.8%. After the induced system crash, anammox-MBR performance recovered steadily to 93.2% nitrogen removal with a 1.25 RatioNH4+-N:NO2−-N and a low nitrite influent concentration of 80 mg/L NO2−-N. Metagenomics analysis revealed that a probable causality of the decreasing nitrogen removal efficiency in Stage 1 was the overgrowth of DNRA-capable bacteria. The results showed that the members within the Ignavibacteriales order (21.7%) out competed anammox bacteria (17.0%) in the anammox-MBR with elevated nitrite concentrations in the effluent. High NO2−-N loading (120 mg N/L) further caused the predominant Candidatus Kuenenia spp. were replaced by Candidatus Brocadia spp. Therefore, it was evident that DNRA bacteria posed negative effects on anammox with 1.60 RatioNH4+-N: NO2−-N. Also, when 120 mg/L NO2−-N fed to anammox-MBR (RatioNH4+-N: NO2−-N = 1.33), canonical denitrification became the primary nitrogen sink with both DNRA and anammox activities decreased. They probably fed on lysed microbial cells of anammox and DNRA. In Stage 3, a low RatioNH4+-N: NO2−-N (1.25) with 80 mg/L NO2−-N was used to rescue the system, which effectively promoted DNRA-capable bacteria growth. Although anammox bacteria's abundance was only 7.7% during this stage, they could be responsible for about 90% of the total nitrogen removal during this stage.
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The suppression of types I and III interferon (IFN) responses by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) contributes to the pathogenesis of coronavirus disease 2019 (COVID‐19). ...The strategy used by SARS‐CoV‐2 to evade antiviral immunity needs further investigation. Here, we reported that SARS‐CoV‐2 ORF9b inhibited types I and III IFN production by targeting multiple molecules of innate antiviral signaling pathways. SARS‐CoV‐2 ORF9b impaired the induction of types I and III IFNs by Sendai virus and poly (I:C). SARS‐CoV‐2 ORF9b inhibited the activation of types I and III IFNs induced by the components of cytosolic dsRNA‐sensing pathways of RIG‐I/MDA5‐MAVS signaling, including RIG‐I, MDA‐5, MAVS, TBK1, and IKKε, rather than IRF3‐5D, which is the active form of IRF3. SARS‐CoV‐2 ORF9b also suppressed the induction of types I and III IFNs by TRIF and STING, which are the adaptor protein of the endosome RNA‐sensing pathway of TLR3‐TRIF signaling and the adaptor protein of the cytosolic DNA‐sensing pathway of cGAS–STING signaling, respectively. A mechanistic analysis revealed that the SARS‐CoV‐2 ORF9b protein interacted with RIG‐I, MDA‐5, MAVS, TRIF, STING, and TBK1 and impeded the phosphorylation and nuclear translocation of IRF3. In addition, SARS‐CoV‐2 ORF9b facilitated the replication of the vesicular stomatitis virus. Therefore, the results showed that SARS‐CoV‐2 ORF9b negatively regulates antiviral immunity and thus facilitates viral replication. This study contributes to our understanding of the molecular mechanism through which SARS‐CoV‐2 impairs antiviral immunity and provides an essential clue to the pathogenesis of COVID‐19.
The capability of different strains derived from soil, activated sludge, farm sludge, and worms’ excreta were investigated for biodegradation of high-density polyethylene, polystyrene foam, ...polypropylene and polyethylene terephthalate in unstimulated and stimulated conditions. Biodegradation using naturally occurring microbial strains examined in mixed (270 days) and individual (100 days) systems, while H2O2 stimulated strains were tested only in the mixed system (30 days). Penicillium raperi, Aspergillus flavus, Penicillium glaucoroseum and Pseudomonas sp. were isolated as the most plastic degrading microbes. Maximum weight loss was seen by incubation of polyethylene with Aspergillus flavus (5.5%) in unstimulated mix condition. Fourier Transform Infrared Spectroscopy (FT-IR) revealed formation of new functional groups as hydroxyl, carbonyl, alkene and alkoxy in the treated plastics. Visualisation of plastics by optical, atomic force (AFM) and electron microscopy (SEM) were also illustrated biodegradation. The derived by-products from microbial degradation was tested, and found no inhibition on microbial growth and performance.
•Penicillium, Aspergillus and Pseudomonas sp. isolated as plastic degrading strains.•The isolated strains showed biofilm formation and ability to degrade PET, PS and PE.•A higher surface degradation was observed using the mixed microbial systems.•Maximum 5.5% weight loss of HD-PE obtained within 100 days.•Stimulation can reduce degradation time with having 2.5% weight loss in 30 days.
The ongoing outbreak of a new coronavirus (2019‐nCoV, or severe acute respiratory syndrome coronavirus 2 SARS‐CoV‐2) has caused an epidemic of the acute respiratory syndrome known as coronavirus ...disease (COVID‐19) in humans. SARS‐CoV‐2 rapidly spread to multiple regions of China and multiple other countries, posing a serious threat to public health. The spike (S) proteins of SARS‐CoV‐1 and SARS‐CoV‐2 may use the same host cellular receptor, angiotensin‐converting enzyme 2 (ACE2), for entering host cells. The affinity between ACE2 and the SARS‐CoV‐2 S protein is much higher than that of ACE2 binding to the SARS‐CoV S protein, explaining why SARS‐CoV‐2 seems to be more readily transmitted from human to human. Here, we report that ACE2 can be significantly upregulated after infection of various viruses, including SARS‐CoV‐1 and SARS‐CoV‐2, or by the stimulation with inflammatory cytokines such as interferons. We propose that SARS‐CoV‐2 may positively induce its cellular entry receptor, ACE2, to accelerate its replication and spread; high inflammatory cytokine levels increase ACE2 expression and act as high‐risk factors for developing COVID‐19, and the infection of other viruses may increase the risk of SARS‐CoV‐2 infection. Therefore, drugs targeting ACE2 may be developed for the future emerging infectious diseases caused by this cluster of coronaviruses.
Highlights
Virus infection and inflammatory cytokines can stimulate angiotensin‐converting enzyme 2 (ACE2) expression. ACE2 is upregulated by the activation of RNA‐sensing pathways. ACE2 is a novel interferon‐stimulated gene (ISG). The increase in ACE2 induced by various viruses and inflammatory cytokines may facilitate severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection and spreading.
Non-degradable plastics such as polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) are among the most generated plastic wastes in municipal and industrial ...waste streams. The mismanagement of abandoned plastics and toxic plastic additives have threatened marine and land fauna as well as human beings for several decades. The available thermal processes can degrade plastic at pilot- and commercial-scale. However, they are energy-intensive and can generate toxic gases. Degradation of plastic waste with the help of live microorganisms (biodegradation) is an eco- and environmentally friendly method for plastic degradation, although the slow processing time and low degradation rate still hinder its applications at pilot- and large-scale. In this review, the advantages and limitations of current plastic degradation methods, their technology readiness levels (TRL), biodegradation mechanisms and the associated challenges in biodegradation are assessed in detail. Based on this analysis, a path toward an efficient and greener way toward degradation of non-recyclable single-use PE, PP, PS and PET plastic is proposed.
•Thermal technologies while degrade plastics in full scale are energy intensive.•Biodegradation is the most environmentally friendly way of plastic degradation.•The current low biodegradation efficiency limits its potential in commercial scale.•Enzyme engineering, aging and biosurfactant can enhance biodegradation rate.
A characteristic feature of COVID‐19, the disease caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection, is the dysregulated immune response with impaired type I and III ...interferon (IFN) expression and an overwhelming inflammatory cytokine storm. RIG‐I‐like receptors (RLRs) and cGAS–STING signaling pathways are responsible for sensing viral infection and inducing IFN production to combat invading viruses. Multiple proteins of SARS‐CoV‐2 have been reported to modulate the RLR signaling pathways to achieve immune evasion. Although SARS‐CoV‐2 infection also activates the cGAS–STING signaling by stimulating micronuclei formation during the process of syncytia, whether SARS‐CoV‐2 modulates the cGAS–STING pathway requires further investigation. Here, we screened 29 SARS‐CoV‐2‐encoded viral proteins to explore the viral proteins that affect the cGAS–STING signaling pathway and found that SARS‐CoV‐2 open reading frame 10 (ORF10) targets STING to antagonize IFN activation. Overexpression of ORF10 inhibits cGAS–STING‐induced interferon regulatory factor 3 phosphorylation, translocation, and subsequent IFN induction. Mechanistically, ORF10 interacts with STING, attenuates the STING–TBK1 association, and impairs STING oligomerization and aggregation and STING‐mediated autophagy; ORF10 also prevents the endoplasmic reticulum (ER)‐to‐Golgi trafficking of STING by anchoring STING in the ER. Taken together, these findings suggest that SARS‐CoV‐2 ORF10 impairs the cGAS–STING signaling by blocking the translocation of STING and the interaction between STING and TBK1 to antagonize innate antiviral immunity.
Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has quickly spread worldwide and has affected more than 10 million individuals. A typical ...feature of COVID-19 is the suppression of type I and III interferon (IFN)-mediated antiviral immunity. However, the molecular mechanism by which SARS-CoV-2 evades antiviral immunity remains elusive. Here, we reported that the SARS-CoV-2 membrane (M) protein inhibits the production of type I and III IFNs induced by the cytosolic dsRNA-sensing pathway mediated by RIG-I/MDA-5-MAVS signaling. In addition, the SARS-CoV-2 M protein suppresses type I and III IFN induction stimulated by SeV infection or poly (I:C) transfection. Mechanistically, the SARS-CoV-2 M protein interacts with RIG-I, MAVS, and TBK1, thus preventing the formation of the multiprotein complex containing RIG-I, MAVS, TRAF3, and TBK1 and subsequently impeding the phosphorylation, nuclear translocation, and activation of IRF3. Consequently, ectopic expression of the SARS-CoV-2 M protein facilitates the replication of vesicular stomatitis virus. Taken together, these results indicate that the SARS-CoV-2 M protein antagonizes type I and III IFN production by targeting RIG-I/MDA-5 signaling, which subsequently attenuates antiviral immunity and enhances viral replication. This study provides insight into the interpretation of SARS-CoV-2-induced antiviral immune suppression and illuminates the pathogenic mechanism of COVID-19.
Rare earth elements (REEs) have become increasingly important in modern day technologies. Unfortunately, their recycling is currently limited, and the conventional technologies for their extraction ...and purification are exceedingly energy and chemical intensive. New sustainable technologies for REE extraction from both primary and secondary resources would be extremely beneficial. This research investigated a two-stage recovery strategy focused on the recovery of neodymium (Nd) and lanthanum (La) from monazite ore that combines microbially based leaching (using citric acid and spent fungal supernatant) with electrochemical extraction. Pretreating the phosphate-based monazite rock (via roasting) dramatically increased the microbial REE leaching efficiency. Batch experiments demonstrated the effective and continued leaching of REEs by recycled citric acid, with up to 392 mg of Nd L–1 and 281 mg of La L–1 leached during seven consecutive 24 h cycles. Neodymium was further extracted in the catholyte of a three-compartment electrochemical system, with up to 880 mg of Nd L–1 achieved within 4 days (at 40 A m–2). Meanwhile, the radioactive element thorium and counterions phosphate and citrate were separated effectively from the REEs in the anolyte, favoring REE extraction and allowing sustainable reuse of the leaching agent. This study shows a promising technology that is suitable for primary ores and can further be optimized for secondary resources.
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