The support vector machine (SVM) has been widely applied for classification problems in both machine learning and statistics. Despite its popularity, however, SVM has some drawbacks in certain ...situations. In particular, the SVM classifier can be very sensitive to outliers in the training sample. Moreover, the number of support vectors (SVs) can be very large in many applications. To circumvent these drawbacks, we propose the robust truncated hinge loss SVM (RSVM), which uses a truncated hinge loss. The RSVM is shown to be more robust to outliers and to deliver more accurate classifiers using a smaller set of SVs than the standard SVM. Our theoretical results show that the RSVM is Fisher-consistent, even when there is no dominating class, a scenario that is particularly challenging for multicategory classification. Similar results are obtained for a class of margin-based classifiers.
We report a facile method for the antimicrobial modification of a thin-film composite polyamide reverse osmosis (RO) membrane. The membrane surface was first coated with polydopamine (PDA), whose ...reducing catechol groups subsequently immobilized silver ions in situ to form uniformly dispersed silver nanoparticles (AgNPs) inside the coating layer. Agglomeration of AgNPs was not observed despite a high silver loading of 13.3 ± 0.3 μg/cm2 (corresponding to a surface coverage of 18.5% by the nanoparticles). Both diffusion inhibition zone tests and colony formation unit tests showed clear antimicrobial effects of the silver loaded membranes on model bacteria Bacillus subtilis and Escherichia coli. Furthermore, the silver immobilized membrane had significantly enhanced salt rejection compared to the control PDA coated membrane, which is attributed to the preferential formation of AgNPs at defect sides within the PDA layer. This self-healing mechanism can be used to prepare antimicrobial RO membranes with improved salt rejection without scarifying the membrane permeability, which provides a new dimension for membrane surface modification.
is often reported to be one of the major members of microbial communities in various natural and engineered environments. Versatile catabolic capabilities of
have been studied extensively in the last ...decade. In contrast, little is known about the ecological roles and adaptation of
to different environments as well as the virulence of potentially pathogenic
strains. In this study, we provide genomic insights into the potential ecological roles and virulence of
by analysing the entire gene set (pangenome) and the genes present in all genomes (core genome) using 34 genomes of 11 different
species. The analyses revealed that the metabolic pathways enabling
to acquire energy from various nutrient sources are well conserved. Genes for denitrification and ammonification are abundant in
, suggesting that
plays an important role in the nitrogen biogeochemical cycle. They also encode sophisticated redox sensory systems and diverse c-di-GMP controlling systems, allowing them to be able to effectively adjust their biofilm lifestyle to changing environments. The virulence factors in
were found to be highly species-specific. The conserved strategies used by potentially pathogenic
for surface adherence, motility control, nutrient acquisition and stress tolerance were also revealed.
The COVID-19 epidemic had an appropriate impact on tourists' trip psychology and their subsequent behavior in participating in rural tourism activities. The purpose of this paper is to explore the ...types of motivations Chinese tourists have for participating in rural tourism in the context of COVID-19, and to comparatively analyze the similarities and differences in motivations for rural tourism during the epidemic and in normal times. An interpretive paradigm qualitative data collection method was used: semi-structured interviews and focus group discussions. Respondents were 21 tourists, who were selected through purposive and snowball sampling. Through content analysis, we found that rural tourism motivations during the epidemic included both diversified and singular motivations. The pull effect of rural destinations is related to distance and ease of realization. For rural areas in close proximity, a single motivation is sufficient to drive tourists. In addition, we found that there was no "altruistic motivation" for rural tourism during the COVID-19 period, but "altruistic feelings" for the preservation of ancient villages were generated during rural tourism. Finally, we discuss the theoretical and practical significance of this study and make suggestions for future research. The study explains tourists' companionship preferences, activity choices, and affective changes, and provides a basis for the operation and advertising strategies of rural destinations to attract tourists and promote their sustainable development.
Biofilms have been extensively studied in aquatic and clinical environments. However, the complexity of edaphic microenvironment hinders the advances toward understanding the environmental ...functionalities and ecological roles of soil biofilms. In this work, artificial soil was employed to investigate the soil biofilm formation and corresponding impacts on community structure and microbial activities. Our results showed that extracellular polymeric substances (EPS) production was significantly enhanced and micro-meter sized cell aggregates formed with high glucose amendment. Biofilm development exhibited significant effects on the soil microbial processes. 16S rRNA gene sequencing demonstrated the soils with biofilms and free-living cells shared similar microbial communities. But the Shannon diversity and evenness indices of communities with soil biofilms were significantly enhanced by 18.2% and 17.1%. The soil with biofilms also revealed a rapid response to nutrient provision and robust microbial activity, which consumed 65.4% more oxygen in the topsoil (0–1.5 mm). Kinetic respiration analysis showed that the enhanced metabolic activity was attributed to 23-times more active microbes in soil biofilms. In summary, this study revealed that soil biofilms can sustain a diverse and robust community to drive soil biogeochemical processes.
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•High nutrient supply induced less microbial biomass growth, enhanced EPS production and soil biofilm formation.•The microbial diversity and evenness of soil with biofilms was significantly higher than that with free-living cells.•The soil with biofilms revealed an elevated microbial respiration rate and a rapid response to nutrient amendment.•Soil biofilm sustained 40-times more active microbes than that with free-living cells.
Bacterial biofilms are surface-adherent microbial communities in which individual cells are surrounded by a self-produced extracellular matrix of polysaccharides, extracellular DNA (eDNA) and ...proteins. Interactions among matrix components within biofilms are responsible for creating an adaptable structure during biofilm development. However, it is unclear how the interactions among matrix components contribute to the construction of the three-dimensional (3D) biofilm architecture.
DNase I treatment significantly inhibited Bacillus subtilis biofilm formation in the early phases of biofilm development. Confocal laser scanning microscopy (CLSM) and image analysis revealed that eDNA was cooperative with exopolysaccharide (EPS) in the early stages of B. subtilis biofilm development, while EPS played a major structural role in the later stages. In addition, deletion of the EPS production gene epsG in B. subtilis SBE1 resulted in loss of the interaction between EPS and eDNA and reduced the biofilm biomass in pellicles at the air-liquid interface. The physical interaction between these two essential biofilm matrix components was confirmed by isothermal titration calorimetry (ITC).
Biofilm 3D structures become interconnected through surrounding eDNA and EPS. eDNA interacts with EPS in the early phases of biofilm development, while EPS mainly participates in the maturation of biofilms. The findings of this study provide a better understanding of the role of the interaction between eDNA and EPS in shaping the biofilm 3D matrix structure and biofilm formation.
The accumulation of potentially toxic elements (PTEs) in aquatic ecosystems has become a global concern, as PTEs may exert a wide range of toxicological impacts on aquatic organisms. Submerged plants ...and the microorganisms attached to their surfaces, however, have displayed great potential as a means of coping with such pollution. Therefore, it is crucial to understand the transport pathways of PTEs across sediment and organisms as well as their accumulation mechanisms in the presence of submerged plants and their biofilms. The majority of previous studies have demonstrated that submerged plants and their biofilms are indicators of PTE pollution in the aquatic environment, yet relatively little is known about PTE accumulation in epiphytic biofilms. In this review, we describe the transport pathways of PTEs in the aquatic environment in order to offer remarkable insights into bioaccumulation mechanisms in submerged plants and their biofilms. Based on the literature cited in this review, the roles of epiphytic biofilms in bioaccumulation and as an indicator of ecosystem health are discussed.
•PTEs transport through different media in aquatic environments.•Bioaccumulation mechanisms of PTEs were studied for submerged plants and biofilms.•Submerged plants and biofilms served as indicators of PTE pollution.•Potential bioaccumulating and bioindicating roles of epiphytic biofilm is addressed.
Graphical models are frequently used to explore networks, such as genetic networks, among a set of variables. This is usually carried out via exploring the sparsity of the precision matrix of the ...variables under consideration. Penalized likelihood methods are often used in such explorations. Yet, positive-definiteness constraints of precision matrices make the optimization problem challenging. We introduce nonconcave penalties and the adaptive LASSO penalty to attenuate the bias problem in the network estimation. Through the local linear approximation to the nonconcave penalty functions, the problem of precision matrix estimation is recast as a sequence of penalized likelihood problems with a weighted L₁ penalty and solved using the efficient algorithm of Friedman et al. Biostatistics 9 (2008) 432-441. Our estimation schemes are applied to two real datasets. Simulation experiments and asymptotic theory are used to justify our proposed methods.
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•NPs within low concentration threshold significantly promote biofilm formation.•EPS is critical for biofilm tolerance of NPs.•Cells in mature biofilm are more resistant to NPs than ...cells at other stages.•Low level of NPs stimulated the release of biofilm-related signaling molecules.•High content NPs exposure induced genotoxicity and upregulated antioxidant genes.
Elucidating the effects of nanoparticles (NPs) on key bacterial functions not only deepens our understanding of nano-toxicity mechanisms, but also guides us in the design criteria for manufacturing safe nanomaterials. In this study, bacterial growth, biofilm development and the expression of biofilm-related genes were monitored in Pseudomonas putida KT2440, a plant-beneficial bacterium, following exposure to ZnO NPs. Low concentrations of NPs (0.5–30 mg L−1) significantly promoted bacterial growth and biofilm formation, while higher concentrations (>30 mg L−1) significantly inhibited biofilm formation. Confocal laser scanning microscopy revealed that microscope slides coated with 0.5 mg L−1 of ZnO NPs showed enhanced bacterial colonization and biomass production, but at higher concentrations (250 mg L−1), biomass production was about 11 times lower than that of the substrate without NPs. Increased protein and sugar contents of the biofilm matrix corroborated the stimulating effects of low concentrations of ZnO NPs. Physiological data were supported by changes in the expression of genes associated with oxidative stress and biofilm development. ZnO NPs at 0.5 mg L−1 stimulated the expression of quorum sensing, lipopolysaccharide biosynthesis, and antibiotic resistance genes; high concentrations of ZnO NPs (250 mg L−1) down-regulated biofilm formation-related genes and up-regulated antioxidant genes. Our results indicate that long-term release of low concentrations of ZnO NPs to the environment would promote undesired biofilm formation and increased resistance to antibiotics.
•EPS-C, N, P preferentially retained during adsorption and coprecipitation with Fh.•EPS mass uptake and selective fractionation opposite for the two formation pathways.•Proteins and acidic ...polysaccharides selectively retained in adsorption complexes.•Lipids and polysaccharide components selectively retained in coprecipitates.•Differential sorption process of EPS components with Fh revealed by 2D-COS-FTIR.
Recent work shows that microbially-derived compounds constitute a significant fraction of the soil organic matter (OM) pool. These compounds include extracellular polymeric substances (EPS) whose mass can far exceed total microbial cell biomass. Sorption of EPS to soil minerals occurs via adsorption and coprecipitation and contributes to the preservation of OM in the soil environment. Little is known, however, about the sorption mechanisms of EPS and selective retention of different EPS constituents on iron (oxyhydr)oxides, especially during EPS adsorption versus coprecipitation with these reactive soil phases. This study examines how EPS interacts with the ubiquitous soil iron (oxyhydr)oxide ferrihydrite during EPS adsorption and coprecipitation and whether these different EPS-mineral association pathways affect EPS sorption and selective retention, and thus the mobility and fate of microbially-derived OM in the soil environment. We use several complimentary techniques to i) examine EPS-carbon, EPS-nitrogen and EPS-phosphorus sorption and fractionation, ii) visualize spatial relationships between EPS biomolecular classes and ferrihydrite using confocal laser scanning microscopy (CLSM), iii) determine EPS-C speciation and chemical fractionation with ferrihydrite using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and iv) determine functional group interactions with ferrihydrite using Fourier transform infrared spectroscopy (FTIR) combined with two-dimensional correlation spectroscopy (2D-COS) analysis. Results show that the coprecipitation of EPS does not change the ferrihydrite mineralogy, as the main mineral phase for EPS association, but it substantially increases the particle size of EPS-ferrihydrite. A substantial difference in the EPS mass fraction associated with the ferrihydrite is observed between the adsorption and coprecipitation experiments at an initial molar C/Fe ratio >1. The EPS-N is relatively enriched during the adsorption process, while more EPS-C and near-complete EPS-P are fixed in the coprecipitation process. XPS results show that the surface of the ferrihydrite formed through EPS adsorption is preferentially enriched with protein-like components, whereas, the surface of the ferrihydrite formed through EPS coprecipitation is enriched with polysaccharide-like components, which is visually confirmed with CLSM images. NEXAFS results reveal that the carboxylic/amide C-containing components are selectively retained during adsorption, with the aliphatic and O-alkyl C-containing components relatively enriched during coprecipitation. 2D-FTIR-COS results indicate that during EPS adsorption on ferrihydrite the PO functional groups are adsorbed faster than the amide and carboxylate functional groups, while during EPS coprecipitation with ferrihydrite the opposite trend is observed. The findings from this study indicate that the formation pathway of EPS-ferrihydrite associations substantially effects the sorption mechanisms and selective retention of EPS and may thus affect the mobility and fate of microbially-derived carbon (C), nitrogen (N) and phosphorus (P) in soils. These new insights on EPS behaviour at the mineral–water interface might be used to evaluate how microbially-derived compounds like EPS are stabilized by iron (oxyhydr)oxides and how EPS-iron (oxyhydr)oxide couplings might affect the reactivity and cycling of OM in natural environments.
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