Fabrication and structural and magnetic properties of spark plasma sintered group-IV diluted magnetic semiconductor Fe-doped SiGe alloys.

Fe-doped SiGe bulk alloys are fabricated using non-equilibrium spark plasma sintering (SPS) and their structure and ferromagnetic and magneto-transport properties are investigated. X-ray diffraction and high-resolution transmission electron microscope measurements show that the obtained alloys are composed of SiGe polycrystals. Magnetization measurements reveal that the Fe-doped SiGe alloys exhibit ferromagnetism up to 259 K, and their Curie temperature increases with Fe doping concentration up to 8%. Moreover, transport measurements of the Fe-doped SiGe alloys show typical metal-insulator transition characteristics of doped semiconductors as well as anomalous Hall effect and intriguing positive-to-negative magnetoresistance, indicating that the obtained alloys are diluted magnetic semiconductors (DMSs). Our results provide insight into the SPS-prepared Fe-doped SiGe bulk alloys and may be useful for the design, fabrication, and application of group-IV DMSs.

Amyloplast sedimentation repolarizes LAZYs to achieve gravity sensing in plants.

Gravity controls directional growth of plants, and the classical starch-statolith hypothesis proposed more than a century ago postulates that amyloplast sedimentation in specialized cells initiates gravity sensing, but the molecular mechanism remains uncharacterized. The LAZY proteins are known as key regulators of gravitropism, and lazy mutants show striking gravitropic defects. Here, we report that gravistimulation by reorientation triggers mitogen-activated protein kinase (MAPK) signaling-mediated phosphorylation of Arabidopsis LAZY proteins basally polarized in root columella cells. Phosphorylation of LAZY increases its interaction with several translocons at the outer envelope membrane of chloroplasts (TOC) proteins on the surface of amyloplasts, facilitating enrichment of LAZY proteins on amyloplasts. Amyloplast sedimentation subsequently guides LAZY to relocate to the new lower side of the plasma membrane in columella cells, where LAZY induces asymmetrical auxin distribution and root differential growth. Together, this study provides a molecular interpretation for the starch-statolith hypothesis: the organelle-movement-triggered molecular polarity formation.

Development and validation of a contrast-enhanced CT-based radiomics nomogram for differentiating mass-like thymic hyperplasia and low-risk thymoma.

PURPOSE: To explore the efficiency of a contrast-enhanced CT-based radiomics nomogram integrated with radiomics signature and clinically independent predictors to distinguish mass-like thymic hyperplasia (ml-TH) from low-risk thymoma (LRT) preoperatively. METHODS: 135 Patients with histopathology confirmed ml-TH (n = 65) and LRT (n = 70) were randomly divided into training set (n = 94) and validation set (n = 41) at a ratio of 7:3. The least absolute shrinkage and selection operator (LASSO) algorithm was used to obtain the optimal features. Based on the selected features, four machine learning models, support vector machine (SVM), logistic regression (LR), extreme gradient boosting (XGBOOST), and random forest (RF) were constructed. Multivariate logistic regression was used to establish a radiomics nomogram containing clinically independent predictors and radiomics signature. Receiver operating characteristic (ROC), DeLong test, and calibration curves were used to detect the performance of the radiomics nomogram in training set and validation set. RESULTS: In the validation set, the area under the curve (AUC) value of LR (0.857; 95% CI: 0.741, 0.973) was the highest of the four machine learning models. Radiomics nomogram containing radiomics signature and clinically independent predictors (including age, shape, and net enhancement degree) had better calibration and identification in the training set (AUC: 0.959; 95% CI: 0.922, 0.996) and validation set (AUC: 0.895; 95% CI: 0.795, 0.996). CONCLUSION: We constructed a contrast-enhanced CT-based radiomics nomogram containing clinically independent predictors and radiomics signature as a noninvasive preoperative prediction method to distinguish ml-TH from LRT. The radiomics nomogram we constructed has potential for preoperative clinical decision making.

Application of DCE-MRI radiomics signature analysis in differentiating molecular subtypes of luminal and non-luminal breast cancer.

Background: The goal of this study was to develop and validate a radiomics signature based on dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) preoperatively differentiating luminal and non-luminal molecular subtypes in patients with invasive breast cancer. Methods: One hundred and thirty-five invasive breast cancer patients with luminal (n = 78) and non-luminal (n = 57) molecular subtypes were divided into training set (n = 95) and testing set (n = 40) in a 7:3 ratio. Demographics and MRI radiological features were used to construct clinical risk factors. Radiomics signature was constructed by extracting radiomics features from the second phase of DCE-MRI images and radiomics score (rad-score) was calculated. Finally, the prediction performance was evaluated in terms of calibration, discrimination, and clinical usefulness. Results: Multivariate logistic regression analysis showed that no clinical risk factors were independent predictors of luminal and non-luminal molecular subtypes in invasive breast cancer patients. Meanwhile, the radiomics signature showed good discrimination in the training set (AUC, 0.86; 95% CI, 0.78-0.93) and the testing set (AUC, 0.80; 95% CI, 0.65-0.95). Conclusion: The DCE-MRI radiomics signature is a promising tool to discrimination luminal and non-luminal molecular subtypes in invasive breast cancer patients preoperatively and noninvasively.

Development and validation of a MRI-based combined radiomics nomogram for differentiation in chondrosarcoma.

Objective: This study aims to develop and validate the performance of an unenhanced magnetic resonance imaging (MRI)-based combined radiomics nomogram for discrimination between low-grade and high-grade in chondrosarcoma. Methods: A total of 102 patients with 44 in low-grade and 58 in high-grade chondrosarcoma were enrolled and divided into training set (n=72) and validation set (n=30) with a 7:3 ratio in this retrospective study. The demographics and unenhanced MRI imaging characteristics of the patients were evaluated to develop a clinic-radiological factors model. Radiomics features were extracted from T1-weighted (T1WI) images to construct radiomics signature and calculate radiomics score (Rad-score). According to multivariate logistic regression analysis, a combined radiomics nomogram based on MRI was constructed by integrating radiomics signature and independent clinic-radiological features. The performance of the combined radiomics nomogram was evaluated in terms of calibration, discrimination, and clinical usefulness. Results: Using multivariate logistic regression analysis, only one clinic-radiological feature (marrow edema OR=0.29, 95% CI=0.11-0.76, P=0.012) was found to be independent predictors of differentiation in chondrosarcoma. Combined with the above clinic-radiological predictor and the radiomics signature constructed by LASSO [least absolute shrinkage and selection operator], a combined radiomics nomogram based on MRI was constructed, and its predictive performance was better than that of clinic-radiological factors model and radiomics signature, with the AUC [area under the curve] of the training set and the validation set were 0.78 (95%CI =0.67-0.89) and 0.77 (95%CI =0.59-0.94), respectively. DCA [decision curve analysis] showed that combined radiomics nomogram has potential clinical application value. Conclusion: The MRI-based combined radiomics nomogram is a noninvasive preoperative prediction tool that combines clinic-radiological feature and radiomics signature and shows good predictive effect in distinguishing low-grade and high-grade bone chondrosarcoma, which may help clinicians to make accurate treatment plans.

Facile Solution-Refluxing Synthesis and Photocatalytic Dye Degradation of a Dynamic Covalent Organic Framework.

Covalent organic frameworks (COFs), as a novel crystalline porous adsorbent, have been attracting significant attention for their synthesis and application exploration due to the advantages of designability, stability, and functionalization. Herein, through increasing the concentration of the acid catalyst, a facile solution-refluxing synthesis method was developed for the preparation of a three-dimensional dynamic COF material, COF-300, with high yields (>90%) and high space−time yields (>28 kg m−3 day−1). This synthesis method not only permits gram-scale synthesis, but also yields products that well maintain porosity and unique guest-dependent dynamic behavior. Moreover, the catalytic activity of COF-300 as a metal-free photocatalyst was explored for the first time. Under 365 nm ultra-violet light irradiation, COF-300 can effectively catalyze the dye degradation (>99%) in wastewater with good recyclability. By adding magnetic Fe3O4 nanoparticles into the solution-refluxing synthesis of COF-300, Fe3O4/COF-300 nanocomposites can be obtained and used as magnetically recyclable photocatalysts, demonstrating the superiority of this facile synthesis procedure. Our study provides new insights for the preparation of COF materials and a constructive exploration for their water treatment application.

Application of a combined radiomics nomogram based on CE-CT in the preoperative prediction of thymomas risk categorization.

Objective: This study aimed to establish a combined radiomics nomogram to preoperatively predict the risk categorization of thymomas by using contrast-enhanced computed tomography (CE-CT) images. Materials and Methods: The clinical, pathological, and CT data of 110 patients with thymoma (50 patients with low-risk thymomas and 60 patients with high-risk thymomas) collected in our Hospital from July 2017 to March 2022 were retrospectively analyzed. The study subjects were randomly divided into the training set (n = 77) and validation set (n = 33) in a 7:3 ratio. Radiomics features were extracted from the CT images, and the least absolute shrinkage and selection operator (LASSO) algorithm was performed to select 13 representative features. Five models, including logistic regression (LR), support vector machine (SVM), random forest (RF), decision tree (DT), and gradient boosting decision tree (GBDT) were constructed to predict thymoma risks based on these features. A combined radiomics nomogram was further established based on the clinical factors and radiomics scores. The performance of the models was evaluated using receiver operating characteristic (ROC) curve, DeLong tests, and decision curve analysis. Results: Maximum tumor diameter and boundary were selected to build the clinical factors model. Thirteen features were acquired by LASSO algorithm screening as the optimal features for machine learning model construction. The LR model exhibited the highest AUC value (0.819) among the five machine learning models in the validation set. Furthermore, the radiomics nomogram combining the selected clinical variables and radiomics signature predicted the categorization of thymomas at different risks more effectively (the training set, AUC = 0.923; the validation set, AUC = 0.870). Finally, the calibration curve and DCA were utilized to confirm the clinical value of this combined radiomics nomogram. Conclusion: We demonstrated the clinical diagnostic value of machine learning models based on CT semantic features and the selected clinical variables, providing a non-invasive, appropriate, and accurate method for preoperative prediction of thymomas risk categorization.

Nomogram Incorporating Contrast-Enhanced Ultrasonography Predicting Time to the Development of Castration-Resistant Prostate Cancer.

BACKGROUND: It is valuable to predict the time to the development of castration-resistant prostate cancer (CRPC) in patients with advanced prostate cancer (PCa). This study aimed to build and validate a nomogram incorporating the clinicopathologic characteristics and the parameters of contrast-enhanced ultrasonography (CEUS) to predict the time to CRPC after androgen deprivation therapy (ADT). METHODS: Patients with PCa were divided into the training (n = 183) and validation cohorts (n = 37) for nomogram construction and validation. The clinicopathologic characteristics and CEUS parameters were analyzed to determine the independent prognosis factors and serve as the basis of the nomogram to estimate the risk of 1-, 2-, and 3-year progress to CRPC. RESULTS: T stage, distant metastasis, Gleason score, area under the curve (AUC), prostate-specific antigen (PSA) nadir, and time to PSA nadir were the independent predictors of CRPC (all P < 0.05). Three nomograms were built to predict the time to CRPC. Owing to the inclusion of CEUS parameter, the discrimination of the established nomogram (C-index: 0.825 and 0.797 for training and validation datasets) was improved compared with the traditional prediction model (C-index: 0.825 and 0.797), and when it excluded posttreatment PSA, it still obtained an acceptable discrimination (C-index: 0.825 and 0.797). CONCLUSIONS: The established nomogram including regular prognostic indicators and CEUS obtained an improved accuracy for the prediction of the time to CRPC. It was also applicable for early prediction of CRPC when it excluded posttreatment PSA, which might be helpful for individualized diagnosis and treatment.

Analysis of melanin biosynthesis in the plant pathogenic fungus Colletotrichum gloeosporioides.

Melanin is recognized as a dark pigment that can protect fungi from the harm of environmental stresses. To investigate what roles of melanin played in the pathogenicity and development of Colletotrichum gloeosporioides, a causal agent of poplar anthracnose, genes encoding a transcription factor CgCmr1 and a polyketide synthase CgPks1 were isolated as the ortholog of Magnaporthe oryzae Pig1 and Pks1 respectively. Deletion of CgCmr1 or CgPks1 resulted in melanin-deficient fungal colony. The ΔCgPks1 mutant showed no melanin accumulation in appressoria, and lack of CgCmr1 also resulted in the delayed and decreased melanization of appressoria. In addition, the turgor pressure of the appressorium was lower in ΔCgPks1 and ΔCgCmr1 than in the wild-type (WT). However, DHN melanin was not a vital factor for virulence in C. gloeosporioides. Moreover, deletion of CgCmr1 and CgPks1 resulted in the hypersensitivity to hydrogen peroxide (H2O2) oxidative stress but not to other abiotic stresses. Collectively, these results suggest that CgCmr1 and CgPks1 play an important role in DHN melanin biosynthesis, and melanin was not an essential factor in penetration and pathogenicity in C. gloeosporioides. The data presented in this study will facilitate future evaluations of the melanin biosynthetic pathway and development in filamentous fungi.

Mucin Msb2 cooperates with the transmembrane protein Sho1 in various plant surface signal sensing and pathogenic processes in the poplar anthracnose fungus Colletotrichum gloeosporioides.

Colletotrichum gloeosporioides is a hemibiotrophic ascomycete fungus that causes anthracnose on numerous plants worldwide and forms a specialized infection structure known as an appressorium in response to various plant surface signals. However, the associated mechanism of host surface signal recognition remains unclear. In the present study, three putative sensors, namely the mucin Msb2, the membrane sensor protein Sho1, and the G-protein-coupled receptor Pth11, were identified and characterized. The results showed that CgMsb2 plays a major role in the recognition of various host surface signals; deletion of CgMsb2 resulted in significant defects in appressorium formation, appressorium penetration, cellophane membrane penetration, and pathogenicity. CgSho1 plays a minor role and together with CgMsb2 cooperatively regulates host signal recognition, cellophane membrane penetration, and pathogenicity; deletion of CgSho1 resulted in an expansion defect of infection hyphae. Deletion of CgPth11 in wildtype, ΔCgMsb2, and ΔCgSho1 strains only resulted in a slight defect in appressorium formation at the early stage, and CgPth11 was dispensable for penetration and pathogenicity. However, exogenous cAMP failed to restore the defect of appressorium formation in ΔCgPth11 at the early stage. CgMsb2 contributed to the phosphorylation of the mitogen-activated protein kinase CgMk1, which is essential for infection-associated functions, while CgSho1 was unable to activate CgMk1 alone but rather cooperated with CgMsb2 to activate CgMk1. These data suggest that CgMsb2 contributes to the activation of CgMk1 and has overlapping functions with CgSho1 in plant surface sensing, appressorium formation, and pathogenicity.

CgEnd3 Regulates Endocytosis, Appressorium Formation, and Virulence in the Poplar Anthracnose Fungus Colletotrichum gloeosporioides.

The hemibiotrophic ascomycete fungus Colletotrichum gloeosporioides is the causal agent of anthracnose on numerous plants, and it causes considerable economic losses worldwide. Endocytosis is an essential cellular process in eukaryotic cells, but its roles in C. gloeosporioides remain unknown. In our study, we identified an endocytosis-related protein, CgEnd3, and knocked it out via polyethylene glycol (PEG)-mediated protoplast transformation. The lack of CgEnd3 resulted in severe defects in endocytosis. C. gloeosporioides infects its host through a specialized structure called appressorium, and ΔCgEnd3 showed deficient appressorium formation, melanization, turgor pressure accumulation, penetration ability of appressorium, cellophane membrane penetration, and pathogenicity. CgEnd3 also affected oxidant adaptation and the expression of core effectors during the early stage of infection. CgEnd3 contains one EF hand domain and four calcium ion-binding sites, and it is involved in calcium signaling. A lack of CgEnd3 changed the responses to cell-wall integrity agents and fungicide fludioxonil. However, CgEnd3 regulated appressorium formation and endocytosis in a calcium signaling-independent manner. Taken together, these results demonstrate that CgEnd3 plays pleiotropic roles in endocytosis, calcium signaling, cell-wall integrity, appressorium formation, penetration, and pathogenicity in C. gloeosporioides, and it suggests that CgEnd3 or endocytosis-related genes function as promising antifungal targets.

Mitogen-activated protein kinase cascade CgSte50-Ste11-Ste7-Mk1 regulates infection-related morphogenesis in the poplar anthracnose fungus Colletotrichum gloeosporioides.

The hemibiotrophic pathogen Colletotrichum gloeosporioides is the causal agent of poplar anthracnose and causes considerable economic losses. This fungus infects its host through a specialized structure called an appressorium. In a previous study, we demonstrated that the mitogen-activated protein kinase (MAPK) CgMk1 plays a critical role in appressorium formation and pathogenicity. In this study, we identified three upstream components of CgMk1, the putative adaptor protein CgSte50, MAPKKK CgSte11, and MAPKK CgSte7, and showed that CgSte50, CgSte11, and CgSte7 positively regulate the phosphorylation of CgMk1. Deletion of CgSte50, CgSte11, and CgSte7 resulted in the loss of appressorium formation, penetration of the cellophane membrane, invasive growth and pathogenicity, similar to the defects observed in the CgMk1 mutant. CgSte50, CgSte11, CgSte7 and CgMk1 were also required for polarity during conidial germination. At the initial stage of appressorium formation, the accumulation of reactive oxygen species (ROS) was altered in the CgSte50, CgSte11, CgSte7 and CgMk1 deletion mutants compared with that in wild type (WT). Furthermore, the CgSte50, CgSte11, CgSte7 and CgMk1 deletion mutants manifested pleiotropic defects during vegetative growth; all mutants exhibited albino colonies, and the aerial hyphae had reduced hydrophobicity. In the mutants, autolysis was detected at the colony edge, and septum formation in the hyphae was elevated compared with that in the WT hyphae. Moreover, deletion of CgSte50, CgSte11, CgSte7 and CgMk1 affected vegetative growth under nitrogen-limiting and osmotic stress conditions. CgSte50, CgSte11, and CgSte7 but not CgMk1 were required for the oxidative stress response. Taken together, these results indicate that the CgMk1 MAPK cascade plays vital roles in various important functions in C. gloeosporioides.

A Cdc42 homolog in Colletotrichum gloeosporioides regulates morphological development and is required for ROS-mediated plant infection.

The Rho GTPase Cdc42 is conserved in fungi and plays a key role in regulating polarity establishment, morphogenesis and differentiation. In this study, we identified an ortholog of Cdc42, CgCdc42, and functionally characterized it to determine the role of Cdc42 in the development and pathogenicity of Colletotrichum gloeosporioides, a causal agent of poplar anthracnose. Targeted deletion of CgCdc42 resulted in reduced vegetative growth and dramatic morphological defects, including the formation of elongated conidia and abnormally shaped appressoria. Moreover, CgCdc42 deletion mutants were less virulent on poplar leaves than were wild type. Appressoria formed by ΔCgCdc42 mutants were morphologically abnormal and present in lower numbers on poplar leaves than were those formed by wild type. However, an ROS scavenging assay indicated that the ΔCgCdc42 mutants maintained wild type pathogenicity in the absence of ROS despite having fewer appressoria than wild type, suggesting that the ΔCgCdc42 mutants were deficient in their tolerance of ROS. Additionally, we also found that the distribution of ROS was different after the deletion of CgCdc42, the ΔCgCdc42 mutants were hypersensitive to H2O2, and transcriptional analysis revealed that CgCdc42 is involved in the regulation of ROS-related genes. Furthermore, loss of CgCdc42 caused defects in cell wall integrity and an uneven distribution of chitin. These data collectively suggest that CgCdc42 plays an important role in the regulation of vegetative growth, morphological development, cell wall integrity and ROS-mediated plant infection in C. gloeosporioides.

The Mitogen-Activated Protein Kinase CgMK1 Governs Appressorium Formation, Melanin Synthesis, and Plant Infection of Colletotrichum gloeosporioides.

The fungus Colletotrichum gloeosporiodes infects plant hosts with a specialized cell called an appressorium, which is melanized and required for plant cell wall penetration. Here, we show that the mitogen-activated protein kinase CgMK1 governs appressorium formation and virulence in the poplar anthracnose fungus C. gloeosporioides. Deletion of CgMK1 impairs aerial hyphal growth and biomass accumulation, and CgMK1 is responsible for the expression of melanin biosynthesis-associated genes. CgMK1 deletion mutants are unable to form appressorium and lose the capacity to colonize either wounded or unwounded poplar leaves, leading to loss of virulence. We demonstrate that the exogenous application of cAMP fails to restore defective appressorium formation in the CgMK1 deletion mutants, suggesting that CgMK1 may function downstream or independent of a cAMP-dependent signal for appressorium formation. Moreover, CgMK1 mutants were sensitive to high osmosis, indicating that CgMK1 plays an important role in stress response. We conclude that CgMK1 plays a vital role in regulating appressorium formation, melanin biosynthesis, and virulence in C. gloeosporiodes.

Histamine downregulates aquaporin 5 in human nasal epithelial cells.

BACKGROUND: Aquaporin 5 (AQP5) is a water-specific channel protein. It is thought to be a key participant in fluid secretion and a rate-limiting barrier to the secretion seen during allergic inflammation. We sought to determine the effect of histamine on AQP5 expression in human nasal epithelial cells (HNEpC). METHODS: HNEpC cells were cultured with four concentrations of histamine in vitro. The phosphorylation of cyclic adenosine monophosphate-responsive element binding protein (CREB) at serine 133 and the AQP5 protein were measured by using immunocytochemistry and Western blotting. Real-time polymerase chain reaction was used to detect AQP5 messenger ribonucleic acid (mRNA). RESULTS: Concentration-dependent histamine induced-inhibition of CREB phosphorylation at serine 133 in HNEpC cells was observed, and AQP5 mRNA and protein were also downregulated in a concentration-dependent fashion. CONCLUSION: Histamine downregulates AQP5 production in HNEpC cells by inhibiting CREB phosphorylation at serine 133.

Hes1, an important gene for activation of hepatic stellate cells, is regulated by Notch1 and TGF-ß/BMP signaling.

AIM: To determine the role of Notch1 and Hes1 in regulating the activation of hepatic stellate cells (HSCs) and whether Hes1 is regulated by transforming growth factor (TGF)/bone morphogenetic protein (BMP) signaling. METHODS: Immunofluorescence staining was used to detect the expression of desmin, glial fibrillary acidic protein and the myofibroblastic marker α-smooth muscle actin (α-SMA) after freshly isolated, normal rat HSCs had been activated in culture for different numbers of days (0, 1, 3, 7 and 10 d). The expression of α-SMA, collagen1α2 (COL1α2), Notch receptors (Notch1-4), and the Notch target genes Hes1 and Hey1 were analyzed by reverse transcriptase-polymerase chain reaction. Luciferase reporter assays and Western blot were used to study the regulation of α-SMA, COL1α1, COL1α2 and Hes1 by NICD1, Hes1, CA-ALK3, and CA-ALK5 in HSC-T6 cells. Moreover, the effects of inhibiting Hes1 function in HSC-T6 cells using a Hes1 decoy were also investigated. RESULTS: The expression of Notch1 and Hes1 mRNAs was significantly down-regulated during the culture of freshly isolated HSCs. In HSC-T6 cells, Notch1 inhibited the promoter activities of α-SMA, COL1α1 and COL1α2. On the other hand, Hes1 enhanced the promoter activities of α-SMA and COL1α2, and this effect could be blocked by inhibiting Hes1 function with a Hes1 decoy. Furthermore, co-transfection of pcDNA3-CA-ALK3 (BMP signaling activin receptor-like kinase 3) and pcDNA3.1-NICD1 further increased the expression of Hes1 compared with transfection of either vector alone in HSC-T6 cells, while pcDNA3-CA-ALK5 (TGF-ß signaling activin receptor-like kinase 5) reduced the effect of NICD1 on Hes1 expression. CONCLUSION: Selective interruption of Hes1 or maintenance of Hes1 at a reasonable level decreases the promoter activities of α-SMA and COL1α2, and these conditions may provide an anti-fibrotic strategy against hepatic fibrosis.

Achieving nitrogen removal via nitrite in a pilot-scale continuous pre-denitrification plant.

Nitrogen removal via nitrite (the nitrite pathway) is beneficial for carbon-limited biological wastewater treatment plants. However, partial nitrification to nitrite has proven difficult in continuous processes treating domestic wastewater. The nitrite pathway is achieved in this study in a pilot-scale continuous pre-denitrification plant (V=300 L) treating domestic wastewater by controlling the dissolved oxygen (DO) concentration at 0.4-0.7 mg/L. It is demonstrated that the nitrite pathway could be repeatedly and reliably achieved, with over 95% of the oxidized nitrogen compounds at the end of the aerobic zone being nitrite. The nitrite pathway improved the total nitrogen (TN) removal by about 20% in comparison to the nitrate pathway, and also reduced aeration costs by 24%. FISH analysis showed that the nitrite oxidizing bacteria (NOB) population gradually reduced at low DO levels, and reached negligible levels when stable nitrite pathway was established. It is hypothesized that NOB was washed out due to its relatively lower affinity with oxygen. A lag phase was observed in the establishment of the nitrite pathway. Several sludge ages were required for the onset of the nitrite pathway after the application of low DO levels. However, nitrite accumulation increased rapidly after that. A similar lag phase was observed for the upset of the nitrite pathway when a DO concentration of 2-3 mg/L was applied. The nitrite pathway negatively impacted on the sludge settleability. A strong correlation between the sludge volume index and the degree of nitrite accumulation was observed.

The denitrification capability of cluster 1 Defluviicoccus vanus-related glycogen-accumulating organisms.

The denitrification capability of Cluster 1 Defluviicoccus vanus-related glycogen-accumulating organisms (DvGAOs) is investigated. A sequencing batch reactor (SBR) fed with acetate as the sole carbon source was operated under alternating anaerobic-aerobic conditions to enrich Cluster 1 DvGAOs. Fluorescence in situ hybridization (FISH) showed that more than 85% of the bacterial population present in the reactor bound to the probes previously designed for Cluster 1 DvGAOs. A series of batch tests were performed to evaluate the capability of the community to reduce nitrate and nitrite. The tests were carried out both before and after the adaptation of the culture to anoxic conditions, and with both the intracellularly stored carbon and acetate as the electron donors. It was found that Cluster 1 DvGAOs were able to reduce nitrate but most likely unable to reduce nitrite. When un-adapted Cluster 1 DvGAOs were exposed to nitrate for the first time, a lag phase of approximately 4 h occurred, which was likely required for the synthesis of the necessary enzymes.

Anaerobic metabolism of Defluviicoccus vanus related glycogen accumulating organisms (GAOs) with acetate and propionate as carbon sources.

The anaerobic uptake of acetate and propionate as single and dual carbon sources by the putative Defluviicoccus vanus related glycogen accumulating organisms (DvGAOs) is investigated. A high enrichment of DvGAOs, representing 95+/-3% of the bacterial community bound to the EUBMIX probes, was achieved in a lab-scale reactor operated under alternating anaerobic and aerobic conditions with acetate as the sole carbon source. The culture is able to take up both acetate and propionate under anaerobic conditions, and the metabolism in both cases is well described by the metabolic models previously proposed for GAOs and verified with experimental data obtained with other types of GAO cultures. In the simultaneous presence of acetate and propionate, DvGAOs take up these two carbon sources sequentially, with propionate uptake preceding acetate uptake. Through model-based analysis, we hypothesise that DvGAOs prefer propionate in order to maximise their production of polyhydroxyalkanoates (PHAs) with the same glycogen consumption, which would enhance their growth potential in the following aerobic period. Despite a low to negligible consumption of acetate in the presence of large amounts of propionate, the presence of acetate considerably stimulated the uptake of propionate with the rate increased by over 60% in comparison to the case where only propionate was present. This property enhances the competitive capability of DvGAOs in enhanced biological phosphorus removal (EBPR) wastewater treatment systems, given the fact that wastewater typically contains both acetate and propionate.

Short-cut nitrification of domestic wastewater in a pilot-scale A/O nitrogen removal plant.

The feasibility of nitrite accumulation in a pilot-scale A/O (anoxic/oxic) nitrogen removal plant treating domestic wastewater was investigated at various dissolved oxygen (DO) concentrations and pH levels. The results showed that the pH was not a useful operational parameter to realize nitrite accumulation. Significant nitrite accumulation was observed at the low DO concentration range of 0.3-0.8 mg/l and the maximum nitrite accumulation ratio of about 90% occurred at a DO concentration of 0.6 mg/l. This suggests a reduction of 22% in the oxygen consumption, and therefore a considerable saving in aeration. However, the nitrite accumulation was destroyed at the high DO concentration and the resumption was very slow. In addition, the average ammonia removal efficiency reached as high as 93% at the low DO level. Moreover, experimental results indicated that nitrogen could be removed by simultaneous nitrification and denitrification (SND) via nitrite in the aerobic zones at the low DO concentration, with the efficiency of 6-12%.