Search

This paper illuminates the significant question of how the oral commensal Fusobacterium nucleatum adapts to the metabolically changing environments of several extra-oral sites such as placenta and colon to promote various diseases as an opportunistic pathogen. We demonstrate here that the highly conserved Rhodobacter nitrogen-fixation complex, commonly known as Rnf complex, is key to fusobacterial metabolic adaptation and virulence. Genetic disruption of this Rnf complex causes global defects in polymicrobial interaction, biofilm formation, cell growth and morphology, hydrogen sulfide production, and ATP synthesis. Targeted metabolomic profiling demonstrates that the loss of this respiratory enzyme significantly diminishes catabolism of numerous amino acids, which negatively impacts fusobacterial virulence as tested in a preterm birth model in mice.

The Gram-negative anaerobe Fusobacterium nucleatum is a major producer of hydrogen sulfide (H2S), a volatile sulfur compound that causes halitosis. Here, we dissected the genetic determinants of H2S production and its role in bacterial fitness and virulence in this important member of the oral microbiome. F. nucleatum possesses four enzymes, CysK1, CysK2, Hly, and MegL, that presumably metabolize l-cysteine to H2S, and CysK1 was previously shown to account for most H2S production in vitro, based on correlations of enzymatic activities with gene expression at mid-log phase. Our molecular studies showed that cysK1 and megL were highly expressed at the late exponential growth phase, concomitant with high-level H2S production, while the expression levels of the other genes remained substantially lower during all growth phases. Although the genetic deletion of cysK1 without supplementation with a CysK1-catalyzed product, lanthionine, caused cell death, the conditional ΔcysK1 mutant and a mutant lacking hly were highly proficient in H2S production. In contrast, a mutant devoid of megL showed drastically reduced H2S production, and a cysK2 mutant showed only minor deficiencies. Intriguingly, the exposure of these mutants to various antibiotics revealed that only the megL mutant displayed altered susceptibility compared to the parental strain: partial sensitivity to nalidixic acid and resistance to kanamycin. Most significantly, the megL mutant was attenuated in virulence in a mouse model of preterm birth, with considerable defects in the spread to amniotic fluid and the colonization of the placenta and fetus. Evidently, the l-methionine γ-lyase MegL is a major H2S-producing enzyme in fusobacterial cells that significantly contributes to fusobacterial virulence and antibiotic susceptibility. IMPORTANCE Fusobacterium nucleatum is a key commensal anaerobe of the human oral cavity that plays a significant role in oral biofilm development and contributes to additional pathologies at extraoral sites, such as promoting preterm birth and colorectal cancer. Although F. nucleatum is known as a major producer of hydrogen sulfide (H2S), its genetic determinants and physiological functions are not well understood. By a combination of bacterial genetics, biochemical methods, and in vivo models of infection, here, we demonstrate that the l-methionine γ-lyase MegL not only is a major H2S-producing enzyme of F. nucleatum but also significantly contributes to the antibiotic susceptibility and virulence of this organism.

Actinomyces oris plays an important role in oral biofilm development. Like many gram-positive bacteria, A. oris produces a sizable number of surface proteins that are anchored to bacterial peptidoglycan by a conserved transpeptidase named the housekeeping sortase SrtA; however, the biological role of many A. oris surface proteins in biofilm formation is largely unknown. Here, we report that the glycoprotein GspA-a genetic suppressor of srtA deletion lethality-not only promotes biofilm formation but also maintains cell membrane integrity under cation stress. In comparison to wild-type cells, under elevated concentrations of mono- and divalent cations the formation of mono- and multi-species biofilms by mutant cells devoid of gspA was significantly diminished, although planktonic growth of both cell types in the presence of cations was indistinguishable. Because gspA overexpression is lethal to cells lacking gspA and srtA, we performed a genetic screen to identify GspA determinants involving cell viability. DNA sequencing and biochemical characterizations of viable clones revealed that mutations of two critical cysteine residues and a serine residue severely affected GspA glycosylation and biofilm formation. Furthermore, mutant cells lacking gspA were markedly sensitive to sodium dodecyl sulfate, a detergent that solubilizes the cytoplasmic membranes, suggesting the cell envelope of the gspA mutant was altered. Consistent with this observation, the gspA mutant exhibited increased membrane permeability, independent of GspA glycosylation, compared to the wild-type strain. Altogether, the results support the notion that the cell wall-anchored glycoprotein GspA provides a defense mechanism against cation stress in biofilm development promoted by A. oris.

Most Actinobacteria encode a small transmembrane protein, whose gene lies immediately downstream of the housekeeping sortase coding for a transpeptidase that anchors many extracellular proteins to the Gram-positive bacterial cell wall. Here, we uncover the hitherto unknown function of this class of conserved proteins, which we name SafA, as a topological modulator of sortase in the oral Actinobacterium Actinomyces oris. Genetic deletion of safA induces cleavage and excretion of the otherwise predominantly membrane-bound SrtA in wild-type cells. Strikingly, the safA mutant, although viable, exhibits severe abnormalities in cell morphology, pilus assembly, surface protein localization, and polymicrobial interactions-the phenotypes that are mirrored by srtA depletion. The pleiotropic defect of the safA mutant is rescued by ectopic expression of safA from not only A. oris, but also Corynebacterium diphtheriae or Corynebacterium matruchotii. Importantly, the SrtA N terminus harbors a tripartite-domain feature typical of a bacterial signal peptide, including a cleavage motif AXA, mutations in which prevent SrtA cleavage mediated by the signal peptidase LepB2. Bacterial two-hybrid analysis demonstrates that SafA and SrtA directly interact. This interaction involves a conserved motif FPW within the exoplasmic face of SafA, since mutations of this motif abrogate SafA-SrtA interaction and induce SrtA cleavage and excretion as observed in the safA mutant. Evidently, SafA is a membrane-imbedded antagonist of signal peptidase that safeguards and maintains membrane homeostasis of the housekeeping sortase SrtA, a central player of cell surface assembly.

This study explored whether executive functioning skills and maths test anxiety were associated with children's untimed and timed algorithmic computational performance and their discrepancy. It also investigated whether such relations were moderated by children's basic maths fact fluency. One hundred and thirty third-graders were rated by teachers regarding their executive functioning skills. Moreover, they self-reported their maths test anxiety level and were tested on various maths skills. Results showed that for untimed computational performance, working memory was a correlate among children low in basic maths fact fluency, whereas maths test anxiety was a correlate among all children. Planning/organization and maths test anxiety were correlates of timed computational performance, regardless of the basic maths fact fluency level. As for discrepancy in computational performance across the two conditions, maths test anxiety was a correlate among children low in basic maths fact fluency. Implications on how to promote children's algorithmic computation were discussed.

A gram-negative colonizer of the oral cavity, Fusobacterium nucleatum not only interacts with many pathogens in the oral microbiome but also has the ability to spread to extraoral sites including placenta and amniotic fluid, promoting preterm birth. To date, however, the molecular mechanism of interspecies interactions-termed coaggregation-by F. nucleatum and how coaggregation affects bacterial virulence remain poorly defined. Here, we employed genome-wide transposon mutagenesis to uncover fusobacterial coaggregation factors, revealing the intertwined function of a two-component signal transduction system (TCS), named CarRS, and a lysine metabolic pathway in regulating the critical coaggregation factor RadD. Transcriptome analysis shows that CarR modulates a large regulon including radD and lysine metabolic genes, such as kamA and kamD, the expression of which are highly up-regulated in the ΔcarR mutant. Significantly, the native culture medium of ΔkamA or ΔkamD mutants builds up abundant amounts of free lysine, which blocks fusobacterial coaggregation with streptococci. Our demonstration that lysine-conjugated beads trap RadD from the membrane lysates suggests that lysine utilizes RadD as its receptor to act as a metabolic inhibitor of coaggregation. Lastly, using a mouse model of preterm birth, we show that fusobacterial virulence is significantly attenuated with the ΔkamA and ΔcarR mutants, in contrast to the enhanced virulence phenotype observed upon diminishing RadD (ΔradD or ΔcarS mutant). Evidently, F. nucleatum employs the TCS CarRS and environmental lysine to modulate RadD-mediated interspecies interaction, virulence, and nutrient acquisition to thrive in the adverse environment of oral biofilms and extraoral sites.

It is well established that emotion is extensively influenced by language. However, previous studies mainly focus on the first language (L1) rather than the second language (L2). The current study explored whether L2 shapes emotion perception in masked priming paradigm by distinguishing emotion-label words (e.g. fear, pride) and emotion-laden words (e.g. breakup, mother). Twenty-three Chinese-English bilinguals were instructed to judge the valence of the emotional pictures that were followed by masked and briefly presented L2 emotion words. Behavioral results showed that emotional pictures primed by negative emotion-label words were processed faster and more accurate than primed by emotion-laden words. Event-related potential results further revealed that emotional pictures elicited smaller N300 primed by negative emotion-label words than by emotion-laden words. The converging evidence suggests that second language can also modulate emotion perception fast and automatically, and such modulation is dependent on emotion word type.

Sortase enzymes are attractive antivirulence drug targets that attach virulence factors to the surface of Staphylococcus aureus and other medically significant bacterial pathogens. Prior efforts to discover a useful sortase inhibitor have relied upon an in vitro activity assay in which the enzyme is removed from its native site on the bacterial surface and truncated to improve solubility. To discover inhibitors that are effective in inactivating sortases in vivo, we developed and implemented a novel cell-based screen using Actinomyces oris, a key colonizer in the development of oral biofilms. A. oris is unique because it exhibits sortase-dependent growth in cell culture, providing a robust phenotype for high throughput screening (HTS). Three molecules representing two unique scaffolds were discovered by HTS and disrupt surface protein display in intact cells and inhibit enzyme activity in vitro. This represents the first HTS for sortase inhibitors that relies on the simple metric of cellular growth and suggests that A. oris may be a useful platform for discovery efforts targeting sortase.

Based on Messick's (1995) framework of construct validity and responses from 521 teachers in the United States and 580 teachers in China, this study provided evidence of the generalizability aspect of construct validity for the "Classroom Appraisal of Resources and Demands" (CARD) questionnaire originally developed in the United States. Confirmatory factor analysis, factorial invariance testing, and differential item functioning were employed to examine the systematic variation of interpretation by the Chinese and US elementary school teachers with respect to the 65 items in the CARD. Results suggested that responses to CARD follow the same structure from both Chinese and US teachers, and that 83% of items showed no difference. Differences in Chinese and US teachers' interpretations of certain items were discussed with implications to school psychology, school counseling, teacher education, educational administration, and policy research.

Assembly of pili on the gram-positive bacterial cell wall involves 2 conserved transpeptidase enzymes named sortases: One for polymerization of pilin subunits and another for anchoring pili to peptidoglycan. How this machine controls pilus length and whether pilus length is critical for cell-to-cell interactions remain unknown. We report here in Actinomyces oris, a key colonizer in the development of oral biofilms, that genetic disruption of its housekeeping sortase SrtA generates exceedingly long pili, catalyzed by its pilus-specific sortase SrtC2 that possesses both pilus polymerization and cell wall anchoring functions. Remarkably, the srtA-deficient mutant fails to mediate interspecies interactions, or coaggregation, even though the coaggregation factor CafA is present at the pilus tip. Increasing ectopic expression of srtA in the mutant progressively shortens pilus length and restores coaggregation accordingly, while elevated levels of shaft pilins and SrtC2 produce long pili and block coaggregation by SrtA+ bacteria. With structural studies, we uncovered 2 key structural elements in SrtA that partake in recognition of pilin substrates and regulate pilus length by inducing the capture and transfer of pilus polymers to the cell wall. Evidently, coaggregation requires proper positioning of the tip adhesin CafA via modulation of pilus length by the housekeeping sortase SrtA.

The widely conserved LytR-CpsA-Psr (LCP) family of enzymes in Gram-positive bacteria is known to attach glycopolymers, including wall teichoic acid, to the cell envelope. However, it is undetermined if these enzymes are capable of catalyzing glycan attachment to surface proteins. In the actinobacterium Actinomyces oris, an LCP homolog here named LcpA is genetically linked to GspA, a glycoprotein that is covalently attached to the bacterial peptidoglycan by the housekeeping sortase SrtA. Here we show by X-ray crystallography that LcpA adopts an α-β-α structural fold, akin to the conserved LCP domain, which harbors characteristic catalytic arginine residues. Consistently, alanine substitution for these residues, R149 and R266, abrogates GspA glycosylation, leading to accumulation of an intermediate form termed GspALMM, which is also observed in the lcpA mutant. Unlike other LCP proteins characterized to date, LcpA contains a stabilizing disulfide bond, mutations of which severely affect LcpA stability. In line with the established role of disulfide bond formation in oxidative protein folding in A. oris, deletion of vkor, coding for the thiol-disulfide oxidoreductase VKOR, also significantly reduces LcpA stability. Biochemical studies demonstrated that the recombinant LcpA enzyme possesses pyrophosphatase activity, enabling hydrolysis of diphosphate bonds. Furthermore, this recombinant enzyme, which weakly interacts with GspA in solution, catalyzes phosphotransfer to GspALMM Altogether, the findings support that A. oris LcpA is an archetypal LCP enzyme that glycosylates a cell wall-anchored protein, a process that may be conserved in Actinobacteria, given the conservation of LcpA and GspA in these high-GC-content organisms.IMPORTANCE In Gram-positive bacteria, the conserved LCP family enzymes studied to date are known to attach glycopolymers, including wall teichoic acid, to the cell envelope. It is unknown if these enzymes catalyze glycosylation of surface proteins. We show here in the actinobacterium Actinomyces oris by X-ray crystallography and biochemical analyses that A. oris LcpA is an LCP homolog, possessing pyrophosphatase and phosphotransferase activities known to belong to LCP enzymes that require conserved catalytic Arg residues, while harboring a unique disulfide bond critical for protein stability. Importantly, LcpA mediates glycosylation of the surface protein GspA via phosphotransferase activity. Our studies provide the first experimental evidence of an archetypal LCP enzyme that promotes glycosylation of a cell wall-anchored protein in Gram-positive bacteria.

Although increasing literature has suggested that emotion-label words (e.g., anger, delight) and emotion-laden words (e.g., thief, bride) were processed differently in native language (L1), there was a lack of neuroimaging evidence showing such differences in second language (L2). The current study compared the cortical responses to emotion-label words and emotion-laden words in L2 using event-related potentials (ERPs) technique. Sixteen Chinese-English bilingual college students were asked to finish a lexical decision task with their brain activations recorded. Overall, emotion-label words and emotion-laden words showed diverse processing characteristics. Specifically, such differences were evidenced by the results that (1) larger N170 was elicited by negative emotion-label words than by negative emotion-laden words while positive emotion-laden words evoked larger N170 than positive emotion-label words at occipito-temporal sites, and (2) emotion-laden words evoked larger Late Positive Complex (LPC) than emotion-label words at parietal sites over the right hemisphere. The implication of the current findings was also discussed.

Fusobacterium nucleatum is a key member of the human oral biofilm. It is also implicated in preterm birth and colorectal cancer. To facilitate basic studies of fusobacterial virulence, we describe here a versatile transposon mutagenesis procedure and a pilot screen for mutants defective in biofilm formation. Out of 10 independent biofilm-defective mutants isolated, the affected genes included the homologs of the Escherichia coli cell division proteins FtsX and EnvC, the electron transport protein RnfA, and four proteins with unknown functions. Next, a facile new gene deletion method demonstrated that nonpolar, in-frame deletion of ftsX or envC produces viable bacteria that are highly filamentous due to defective cell division. Transmission electron and cryo-electron microscopy revealed that the ΔftsX and ΔenvC mutant cells remain joined with apparent constriction, and scanning electron microscopy (EM) uncovered a smooth cell surface without the microfolds present in wild-type cells. FtsX and EnvC proteins interact with each other as well as a common set of interacting partners, many with unknown function. Last, biofilm development is altered when cell division is blocked by MinC overproduction; however, unlike the phenotypes of ΔftsX and ΔenvC mutants, a weakly adherent biofilm is formed, and the wild-type rugged cell surface is maintained. Therefore, FtsX and EnvC may perform novel functions in Fusobacterium cell biology. This is the first report of an unbiased approach to uncover genetic determinants of fusobacterial biofilm development. It points to an intriguing link among cytokinesis, cell surface dynamics, and biofilm formation, whose molecular underpinnings remain to be elucidated.IMPORTANCE Little is known about the virulence mechanisms and associated factors in F. nucleatum, due mainly to the lack of convenient genetic tools for this organism. We employed two efficient genetic strategies to identify F. nucleatum biofilm-defective mutants, revealing FtsX and EnvC among seven biofilm-associated factors. Electron microscopy established cell division defects of the ΔftsX and ΔenvC mutants, accompanied with a smooth cell surface, unlike the microfold, rugged appearance of wild-type bacteria. Proteomic studies demonstrated that FtsX and EnvC interact with each other as well as a set of common and unique interacting proteins, many with unknown functions. Importantly, blocking cell division by MinC overproduction led to formation of a weakly adherent biofilm, without alteration of the wild-type cell surface. Thus, this work links cell division and surface dynamics to biofilm development and lays a foundation for future genetic and biochemical investigations of basic cellular processes in this clinically significant pathogen.

The Gram-positive actinobacteria Actinomyces spp. are key colonizers in the development of oral biofilms due to the inherent ability of Actinomyces to adhere to receptor polysaccharides on the surface of oral streptococci and host cells. This receptor-dependent bacterial interaction, or coaggregation, requires a unique sortase-catalyzed pilus consisting of the pilus shaft FimA and the coaggregation factor CafA forming the pilus tip. While the essential role of the sortase machine SrtC2 in pilus assembly, biofilm formation, and coaggregation has been established, little is known about trans-acting factors contributing to these processes. We report here a large-scale Tn5 transposon screen for mutants defective in Actinomyces oris coaggregation with Streptococcus oralis We obtained 33 independent clones, 13 of which completely failed to aggregate with S. oralis, and the remainder of which exhibited a range of phenotypes from severely to weakly defective coaggregation. The former had Tn5 insertions in fimA, cafA, or srtC2, as expected; the latter were mapped to genes coding for uncharacterized proteins and various nuo genes encoding the NADH dehydrogenase subunits. Electron microscopy and biochemical analyses of mutants with nonpolar deletions of nuo genes and ubiE, a menaquinone C-methyltransferase-encoding gene downstream of the nuo locus, confirmed the pilus and coaggregation defects. Both nuoA and ubiE mutants were defective in oxidation of MdbA, the major oxidoreductase required for oxidative folding of pilus proteins. Furthermore, supplementation of the ubiE mutant with exogenous menaquinone-4 rescued the cell growth and pilus defects. Altogether, we propose that the A. oris electron transport chain is biochemically linked to pilus assembly via oxidative protein folding.IMPORTANCE The Gram-positive actinobacterium A. oris expresses adhesive pili, or fimbriae, that are essential to biofilm formation and Actinomyces interactions with other bacteria, termed coaggregation. While the critical role of the conserved sortase machine in pilus assembly and the disulfide bond-forming catalyst MdbA in oxidative folding of pilins has been established, little is known about other trans-acting factors involved in these processes. Using a Tn5 transposon screen for mutants defective in coaggregation with Streptococcus oralis, we found that genetic disruption of the NADH dehydrogenase and menaquinone biosynthesis detrimentally alters pilus assembly. Further biochemical characterizations determined that menaquinone is important for reactivation of MdbA. This study supports the notion that the electron transport chain is biochemically linked to pilus assembly in A. oris via oxidative folding of pilin precursors.

The connection between gene loss and the functional adaptation of retained proteins is still poorly understood. We apply phylogenomics and metabolic modeling to detect bacterial species that are evolving by gene loss, with the finding that Actinomycetaceae genomes from human cavities are undergoing sizable reductions, including loss of L-histidine and L-tryptophan biosynthesis. We observe that the dual-substrate phosphoribosyl isomerase A or priA gene, at which these pathways converge, appears to coevolve with the occurrence of trp and his genes. Characterization of a dozen PriA homologs shows that these enzymes adapt from bifunctionality in the largest genomes, to a monofunctional, yet not necessarily specialized, inefficient form in genomes undergoing reduction. These functional changes are accomplished via mutations, which result from relaxation of purifying selection, in residues structurally mapped after sequence and X-ray structural analyses. Our results show how gene loss can drive the evolution of substrate specificity from retained enzymes.

In the present study, we examined modulations of the second language (L2) positive emotion-label words, positive emotion-laden words, and neutral words on conflict processing in a flanker task. Twenty Chinese-English bilinguals were instructed to decide the color of the central words that were vertically surrounded by the same words with the same or different color. During the task, their cortical activation was recorded. The result showed that L2 positive emotion-laden words elicited different brain activations from emotion-label words and neutral words at both early and late stages. Differential modulations on conflict processing between positive emotion-label words and positive emotion-laden words in the L2 existed even after approach-motivation intensity was controlled. These results suggest emotion word type affects conflict processing, even in L2.

By synthesizing existing behavioural studies through a meta-analytic approach, the current study compared the performances of Autism spectrum disorder (ASD) and typically developing groups in audiovisual speech integration and investigated potential moderators that might contribute to the heterogeneity of the existing findings. In total, nine studies were included in the current study, and the pooled overall difference between the two groups was significant, g = - 0.835 (p < 0.001; 95% CI - 1.155 to - 0.516). Age and task scoring method were found to be associated with the inconsistencies of the findings reported by previous studies. These findings indicate that individuals with ASD show weaker McGurk effect than typically developing controls.

In an endeavor to tackle the limitations of fixed collaborative scripts and to further support collaborative learning practices, adaptive collaborative scripts have been implemented within the educational domain. However, the divergent findings surrounding the efficacy of adaptive collaborative scripts engendered a compelling need for a comprehensive understanding of the adaptive scripts. This study explored the effectiveness of adaptive scripts through a systematic analysis of 11 meticulously chosen studies and demonstrated the distinct contributions offered by varying types of adaptive collaborative scripts (namely, fading-out scripts, adaptable scripts, and self-adaptive scripts). The results underscored adaptive scripts yielded a favorable impact on the caliber of collaboration and on learners’ psychological contentment. Nonetheless, the ramifications on learning outcomes were inconclusive. Under the guidance of activity theory, this review uncovered the optimal application conditions of each variant of adaptive script. The fading-out scripts necessitated supplementary consistent support to ensure satisfactory learning outcomes. Adaptable scripts demonstrated stable efficacy when employed for students with good self-regulation ability. The self-adaptive scripts yielded optimal results in learning activities with higher-level educational objectives. Distributed roles within learning groups and perceived adaptivity also influenced the efficacy of self-adaptive scripts. Implications, limitations, and future directions were also provided. [ABSTRACT FROM AUTHOR]

Endotracheal intubation holds significant importance in trauma point care and emergency medicine. However, laryngeal injury and subsequent chronic complications can result from the friction between the mucosa and the tube during intubation. Here we present a lubricant coating based on hyaluronic acid. Inspired by mussels, hyaluronic acid was first conjugated with dopamine to obtain HD, and then a triblock copolymer Pluronic F127 (F127) was complexed with HD to form a micelle layer. Dopamine can assist coating deposition on the tube under weak alkaline conditions, while improving the coating stability. The micelle layer formed by F127 and HD provides excellent water retention and lubrication performance. The friction coefficient of the HD-F127 coating was 56% lower than that of the control, as determined by a friction performance test. Laryngeal injury and subsequent chronic complications can result from the friction between the mucosa and the tube during intubation. Here we present a lubricant coating based on hyaluronic acid. The HD-F127 coatings have great potential in biomedical devices that require lubrication, due to their simple fabrication method and excellent lubrication properties. (Image credit: Wu Chenggang.) [ABSTRACT FROM AUTHOR]