TagP, a PAAR-domain containing protein, plays roles in the fitness and virulence of Acinetobacter baumannii.

Background: Type VI secretion system (T6SS) is widely present in Gram-negative bacteria and directly mediates antagonistic prokaryote interactions. PAAR (proline-alanine-alanine-arginine repeats) proteins have been proven essential for T6SS-mediated secretion and target cell killing. Although PAAR proteins are commonly found in A. baumannii, their biological functions are not fully disclosed yet. In this study, we investigated the functions of a PAAR protein termed TagP (T6SS-associated-gene PAAR), encoded by the gene ACX60_RS09070 outside the core T6SS locus of A. baumannii strain ATCC 17978. Methods: In this study, tagP null and complement A. baumannii ATCC 17978 strains were constructed. The influence of TagP on T6SS function was investigated through Hcp detection and bacterial competition assay; the influence on environmental fitness was studied through in vitro growth, biofilm formation assay, surface motility assay, survivability in various simulated environmental conditions; the influence on pathogenicity was explored through cell adhesion and invasion assays, intramacrophage survival assay, serum survival assay, and G. melonella Killing assays. Quantitative transcriptomic and proteomic analyses were utilized to observe the global impact of TagP on bacterial status. Results: Compared with the wildtype strain, the tagP null mutant was impaired in several tested phenotypes such as surface motility, biofilm formation, tolerance to adverse environments, adherence to eukaryotic cells, endurance to serum complement killing, and virulence to Galleria melonella. Notably, although RNA-Seq and proteomics analysis revealed that many genes were significantly down-regulated in the tagP null mutant compared to the wildtype strain, there is no significant difference in their antagonistic abilities. We also found that Histone-like nucleoid structuring protein (H-NS) was significantly upregulated in the tagP null mutant at both mRNA and protein levels. Conclusions: This study enriches our understanding of the biofunction of PAAR proteins in A. baumannii. The results indicates that TagP involved in a unique modulation of fitness and virulence control in A. baumannii, it is more than a classic PAAR protein involved in T6SS, while how TagP play roles in the fitness and virulence of A. baumannii needs further investigation to clarify.

Structure and assembly of type VI secretion system cargo delivery vehicle.

Type VI secretion system is widely used in Gram-negative bacteria for injecting toxic effectors into neighboring prokaryotic or eukaryotic cells. Various effectors can be loaded onto the T6SS delivery tube via its core components: Hcp, VgrG, or PAAR. Here, we report 2.8-Å resolution cryo-EM structure of intact T6SS Hcp5-VgrG-PAAR cargo delivery system and crystal structure of unbound Hcp5 from B. fragilis NCTC 9343. Loading of Hcp5 hexameric ring onto VgrG causes expansion of its inner cavity and external surface, explaining how structural changes could be propagated to regulate co-polymerization and surrounding contractile sheath. High-affinity binding between Hcp and VgrG causes entropically unfavorable structuring of long loops. Furthermore, interactions between VgrG trimer and Hcp hexamer are asymmetric, with three of the six Hcp monomers exhibiting a major loop flip. Our study provides insights into the assembly, loading, and firing of T6SS nanomachine that contributes to bacterial inter-species competition and host interactions.

VgrG Spike Dictates PAAR Requirement for the Assembly of the Type VI Secretion System.

Widely employed by Gram-negative pathogens for competition and pathogenesis, the type six protein secretion system (T6SS) can inject toxic effectors into neighboring cells through the penetration of a spear-like structure comprising a long Hcp tube and a VgrG-PAAR spike complex. The cone-shaped PAAR is believed to sharpen the T6SS spear for penetration but it remains unclear why PAAR is required for T6SS functions in some bacteria but dispensable in others. Here, we report the conditional requirement of PAAR for T6SS functions in Aeromonas dhakensis, an emerging human pathogen that may cause severe bacteremia. By deleting the two PAAR paralogs, we show that PAAR is not required for T6SS secretion, bacterial killing, or specific effector delivery in A. dhakensis. By constructing combinatorial PAAR and vgrG deletions, we demonstrate that deletion of individual PAAR moderately reduced T6SS functions but double or triple deletions of PAAR in the vgrG deletion mutants severely impaired T6SS functions. Notably, the auxiliary-cluster-encoded PAAR2 and VgrG3 are less critical than the main-cluster-encoded PAAR1 and VgrG1&2 proteins to T6SS functions. In addition, PAAR1 but not PAAR2 contributes to antieukaryotic virulence in amoeba. Our data suggest that, for a multi-PAAR T6SS, the variable role of PAAR paralogs correlates with the VgrG-spike composition that collectively dictates T6SS assembly. IMPORTANCE Gram-negative bacteria often encode multiple paralogs of the cone-shaped PAAR that sits atop the VgrG-spike and is thought to sharpen the spear-like T6SS puncturing device. However, it is unclear why PAAR is required for the assembly of some but not all T6SSs and why there are multiple PAARs if they are not required. Our data delineate a VgrG-mediated conditional requirement for PAAR and suggest a core-auxiliary relationship among different PAAR-VgrG modules that may have been acquired sequentially by the T6SS during evolution.

Inner-outer couple: anima and animus revisited. New perspectives for a clinical approach in transition.

The conflicts of the outer couple (crises, separations, divorces) with a high incidence in the rates of depression, reveal the archetypal dysfunction of the relationship between the inner-couple (in-shadow) and the outer-couple (in-crisis). To understand this in depth, a new animated and integrated model of the masculine (animus) and the feminine (anima) is explored. It is a transformational model, in which Jung's contributions are integrated and understood as knowledge in transition. Masculine and feminine cosmogonic principles are personified in the human psyche as anima-animus archetypes-complexes. Their relationship, mediated by the binding eros (cosmogonic-eros), configures the inner-couple-complex. Masculine and feminine are differentiations of the Self energy, present in both men and women. In the conscious dimension, they structure the ego-anima-animus identity; in the dimension of the personal unconscious, the anima-animus complexes; and at the archetypal level, the deep identity of the primordial feminine/masculine. In this initial restructured model, the anima-animus relationship and the description of the dual quaternity as the dynamics of the inner-outer couple interrelation are especially significant. The breadth and comprehensive richness of the new model is illustrated in the clinical/dream material of a patient under analysis, presenting the dynamics: inner couple in shadow - outer couple in crisis.

Les conflits du couple extérieur (crises, séparations, divorces) avec une forte incidence du taux de dépression révèlent le dysfonctionnement archétypal de la relation entre le couple intérieur (dans l'ombre) et le couple extérieur (dans la crise). Pour une compréhension profonde de ceci nous étudions un modèle nouveau, animé et intégré, du masculin (animus) et du féminin (anima). Il s'agit d'un modèle de transformation dans lequel les apports de Jung sont intégrés et compris en tant que savoir en transition. Les principes cosmogoniques de masculin et féminin sont personifiés dans la psyché humaine comme archétypes-complexes anima-animus. Leur relation, médiée par Eros qui relie (cosmogonique-eros) configure les complexes couples intérieur-extérieur. Masculin et féminin sont des différentiations de l'énergie du Soi, présent à la fois chez les hommes et les femmes. Ils structurent, dans la dimension consciente, l'identité du moi-anima-animus dans la dimension de l'inconscient personnel, les complexes anima-animus, et au niveau archétypal, l'identité profonde du féminin/masculin primordial. Dans ce modèle initial restructuré, la relation anima-animus est particulièrement significative, ainsi que la description de la quaternité duale en tant que/comme dynamique de l'interrelation couple intérieur-extérieur. L'amplitude et la richesse inclusive du nouveau modèle est illustrée dans le matériel clinique et les rêves d'un patient en analyse et qui présente la dynamique: couple intérieur dans son ombre - couple extérieur en crise.

Los conflictos de la pareja exterior (crisis, separaciones, divorcios,) con alta incidencia en las tasas de depresión, ponen de manifiesto la disfunción arquetípica de la relación pareja-interior (en-sombra) y pareja exterior (en-crisis). Para comprender esto, en profundidad, se explora un nuevo modelo, animado e integrado, de lo masculino (animus) y lo femenino (ánima). Un modelo transformado, donde los aportes de Jung son integrados y comprendidos como conocimientos en transición. Se considera que los principios cosmogónicos masculino y femenino se personifican en la psique humana como arquetipos-complejos ánima-animus. Su relacionamiento, mediado por el eros vinculante (eros-kosmogónico), configura el complejo-pareja-interior. Masculino y femenino son diferenciaciones de la energía sélfica, presentes en hombres y mujeres. Ellas estructuran, en la dimensión consciente, la identidad ego-ánima-animus, en la dimensión de lo inconsciente personal los complejos ánima-animus, y a nivel arquetípico, la identidad profunda de lo femenino/masculino primordial. En el modelo inicial re-estructurado, es especialmente significativo la relación ánima-animus, y la descripción del doble cuaterno como la dinámica de interrelación pareja interior-exterior. La amplitud y riqueza comprensiva del nuevo modelo es ilustrado en el material clínico/onírico de un paciente en análisis que presenta la dinámica pareja interior en sombra- pareja exterior en crisis.

Os conflitos do casal externo (crise, separações, divórcios) com alta incidência nas taxas de depressão revelam a disfunção arquetípica da relação entre o casal interno (na sombra) e o casal externo (em crise). Para entender isso em profundidade, um novo modelo, animado e integrado, do masculino (animus) e do feminino (anima) é explorado. É um modelo transformacional, no qual as contribuições de Jung são integradas e entendidas como conhecimento em transição. Princípios cosmogônicos masculinos e femininos são personificados na psique humana como arquétipos-complexos anima-animus. Sua relação, mediada pelo eros de ligação (cosmogônico-eros), configura o complexo de casal interno. Masculino e feminino são diferenciações da energia do Si Mesmo, presentes em homens e mulheres. Eles estruturam, na dimensão consciente, a identidade ego-anima-animus; na dimensão do inconsciente pessoal, os complexos anima-animus; e no nível arquetípico, a identidade profunda do feminino/masculino primordial. No modelo reestruturado inicial, a relação anima-animus é especialmente significativa, e a descrição da quaternidade dual como a dinâmica da inter-relação interior-exterior do casal. A amplitude e a riqueza abrangente do novo modelo são ilustradas no material clínico/sonho de um paciente em análise, apresentando a dinâmica: casal interno na sombra - casal externo em crise.

More Than Just a Spearhead: Diverse Functions of PAAR for Assembly and Delivery of Toxins of the Contractile Injection Systems.

The type VI secretion system (T6SS) belongs to the evolutionarily related group of contractile injection systems that employ a contractile outer sheath to inject a rigid spear-like inner tube into target bacterial and eukaryotic cells. The tip of the rigid tube is often decorated by a PAAR-repeat protein as a key structural component. Many members of the PAAR protein family can also have additional and diverse functions by serving as toxins for those with extended domains or as carriers for interacting toxins. A plethora of toxin modules or modules of unknown functions have been bioinformatically predicted to be associated with PAAR either as a fused domain or as an interacting partner, and yet only a small number of PAAR proteins have been studied, highlighting the exciting and dire need for future research to better understand the diverse PAAR-mediated functions.

PAAR Proteins Are Versatile Clips That Enrich the Antimicrobial Weapon Arsenals of Prokaryotes.

Protein toxins secreted by prokaryotes have been found to affect the pathogenicity of pathogens or directly mediate antagonistic interactions between prokaryotes. PAAR proteins are important carriers of toxic effectors and are located at the forefront of either the type VI secretion system (T6SS) or the extracellular contractile injection system (eCIS). This study systematically investigated PAAR homologues and related toxic effectors. We found that PAAR homologues were divided into 8 types and 16 subtypes and distributed in 23.1% of bacterial genomes and 7.8% of archaeal genomes. PAAR proteins of all types fold into a highly similar conical structure, even from relatively diverse underlying sequences. PAAR homologues associated with different secretion systems display a mixed phylogenetic relationship, indicating that PAAR proteins from such a subtype can be assembled on either a T6SS or an eCIS. More than 1,300 PAAR-related toxic effector genes were identified; one PAAR subtype can be associated with toxins of over 40 families, and toxins from one family can be associated with more than 10 PAAR subtypes. A large-scale comparison of Earth Microbiome Project data and prokaryotic genomes revealed that prokaryotes encoding PAAR genes are widely present in diverse environments worldwide, and taxa encoding multiple PAAR gene copies exhibit a wider distribution in environments than other taxa. Overall, our studies highlighted that PAAR proteins are versatile clips loaded with antimicrobial toxin bullets for secretion weapons (T6SS and eCIS), greatly enriching the weapon arsenal of prokaryotes, which, often together with VgrG, help prokaryotes fight for survival advantages in crowded environments. IMPORTANCE Infectious diseases caused by microbial pathogens are severe threats to human health and economic development. To respond to these threats, it is necessary to understand how microorganisms survive in and adapt to complex environments. Microorganic toxins, which are widely distributed in nature, are the key weapons in life domain interactions. PAAR proteins are important carriers of prokaryotic toxic effectors. We reveal the versatility of PAAR proteins between secretory systems and the massive diversity of toxic effectors carried by PAAR proteins, which helps prokaryotes enrich their arsenal and expand their ability to attack their neighbors. A large number of PAAR homologues and related toxic effectors enhance the survival competitiveness of prokaryotic populations. In conclusion, our work provides an example for large-scale analysis of the global distribution and ecological functions of prokaryotic functional genes.

Nanobody-aided crystallization of the transcription regulator PaaR2 from Escherichia coli O157:H7.

paaR2-paaA2-parE2 is a three-component toxin-antitoxin module found in prophage CP-993P of Escherichia coli O157:H7. Transcription regulation of this module occurs via the 123-amino-acid regulator PaaR2, which forms a large oligomeric structure. Despite appearing to be well folded, PaaR2 withstands crystallization, as does its N-terminal DNA-binding domain. Native mass spectrometry was used to screen for nanobodies that form a unique complex and stabilize the octameric structure of PaaR2. One such nanobody, Nb33, allowed crystallization of the protein. The resulting crystals belong to space group F432, with unit-cell parameter a = 317 Å, diffract to 4.0 Šresolution and are likely to contain four PaaR2 monomers and four nanobody monomers in the asymmetric unit. Crystals of two truncates containing the N-terminal helix-turn-helix domain also interact with Nb33, and the corresponding co-crystals diffracted to 1.6 and 1.75 Šresolution.

Capacity of a Radio Vortex Communication System Using a Partial Angular Aperture Receiving Scheme under the Horizontal Non-Kolmogorov Model.

A partial receiving scheme based on limited angular aperture multi-beam receiving and demultiplexing can solve the difficulty caused by the divergence of the vortex beam in the conventional whole beam receiving scheme and realize the long-distance transmission of the vortex wave. The propagation of the radio vortex beam in atmospheric turbulence is of significant importance in theoretical study and practical applications. In this paper, the influence of atmospheric turbulence on the performance of a radio vortex (RV) communication system based on a partial angular aperture receiving (PAAR) scheme under the horizontal non-Kolmogorov channel model is studied. The spiral spectrum of the PAAR scheme and the channel capacity of the RV communication system using the PAAR scheme are derived. Simulation results demonstrate that the selected transmission frequency range has a great influence on the RV communication system based on the PAAR scheme, and the choice of the orbital angular momentum (OAM) mode number L has an influence on the propagation distance. The capacity of RV communication systems based on the PAAR scheme increases with the increase of the transmission frequency in the selected transmission frequency range of 10 GHz-60 GHz. When the number of orbital angular momentum (OAM) modes L is small, we can improve the signal-to-noise ratio (SNR) to obtain a larger capacity of the RV communication system based on the PAAR scheme over a longer propagation distance.

Two PAAR Proteins with Different C-Terminal Extended Domains Have Distinct Ecological Functions in Myxococcus xanthus.

Bacterial proline-alanine-alanine-arginine (PAAR) proteins are located at the top of the type VI secretion system (T6SS) nanomachine and carry and deliver effectors into neighboring cells. Many PAAR proteins are fused with a variable C-terminal extended domain (CTD). Here, we report that two paar-ctd genes (MXAN_RS08765 and MXAN_RS36995) located in two homologous operons are involved in different ecological functions of Myxococcus xanthusMXAN_RS08765 inhibited the growth of plant-pathogenic fungi, while MXAN_RS36995 was associated with the colony-merger incompatibility of M. xanthus cells. These two PAAR-CTD proteins were both toxic to Escherichia coli cells, while MXAN_RS08765, but not MXAN_RS36995, was also toxic to Saccharomyces cerevisiae cells. Their downstream adjacent genes, i.e., MXAN_RS08760 and MXAN_RS24590, protected against the toxicities. The MXAN_RS36995 protein was demonstrated to have nuclease activity, and the activity was inhibited by the presence of MXAN_RS24590. Our results highlight that the PAAR proteins diversify the CTDs to play divergent roles in M. xanthusIMPORTANCE The type VI secretion system (T6SS) is a bacterial cell contact-dependent weapon capable of delivering protein effectors into neighboring cells. The PAAR protein is located at the top of the nanomachine and carries an effector for delivery. Many PAAR proteins are extended with a diverse C-terminal sequence with an unknown structure and function. Here, we report two paar-ctd genes located in two homologous operons involved in different ecological functions of Myxococcus xanthus; one has antifungal activity, and the other is associated with the kin discrimination phenotype. The PAAR-CTD proteins and the proteins encoded by their downstream genes form two toxin-immunity protein pairs. We demonstrated that the C-terminal diversification of the PAAR-CTD proteins enriches the ecological functions of bacterial cells.

Autophagy in the control and pathogenesis of parasitic infections.

BACKGROUND: Autophagy has a crucial role in the defense against parasites. The interplay existing between host autophagy and parasites has varied outcomes due to the kind of host cell and microorganism. The presence of autophagic compartments disrupt a significant number of pathogens and are further cleared by xenophagy in an autolysosome. Another section of pathogens have the capacity to outwit the autophagic pathway to their own advantage. RESULT: To comprehend the interaction between pathogens and the host cells, it is significant to distinguish between starvation-induced autophagy and other autophagic pathways. Subversion of host autophagy by parasites is likely due to differences in cellular pathways from those of 'classical' autophagy and that they are controlled by parasites in a peculiar way. In xenophagy clearance at the intracellular level, the pathogens are first ubiquitinated before autophagy receptors acknowledgement, followed by labeling with light chain 3 (LC3) protein. The LC3 in LC3-associated phagocytosis (LAP) is added directly into vacuole membrane and functions regardless of the ULK, an initiation complex. The activation of the ULK complex composed of ATG13, FIP200 and ATG101causes the initiation of host autophagic response. Again, the recognition of PAMPs by conserved PRRs marks the first line of defense against pathogens, involving Toll-like receptors (TLRs). These all important immune-related receptors have been reported recently to regulate autophagy. CONCLUSION: In this review, we sum up recent advances in autophagy to acknowledge and understand the interplay between host and parasites, focusing on target proteins for the design of therapeutic drugs. The target host proteins on the initiation of the ULK complex and PRRs-mediated recognition of PAMPs may provide strong potential for the design of therapeutic drugs against parasitic infections.

Solving the Puzzle: Connecting a Heterologous Agrobacterium tumefaciens T6SS Effector to a Pseudomonas aeruginosa Spike Complex.

The type VI secretion system (T6SS) is a contractile injection apparatus that translocates a spike loaded with various effectors directly into eukaryotic and prokaryotic target cells. Such T6SS spike consists of a needle-shaped trimer of VgrG proteins topped by a conical and sharp PAAR protein that facilitates puncturing of the target membrane. T6SS-delivered effector proteins can be either fused to one of the two spike proteins or interact with either in a highly specific manner. In Agrobacterium tumefaciens the T6SS effector Tde1 is targeted to its cognate VgrG1 protein. Here, we attempted to use a VgrG shuttle to deliver a heterologous T6SS effector by directing Tde1 onto a T6SS spike in Pseudomonas aeruginosa. For this, we designed chimeras between VgrG1 from A. tumefaciens and VgrG1a from P. aeruginosa and showed that modification of the spike protein hampered T6SS functionality in the presence of the Tde1 effector complex. We provide evidence suggesting that Tde1 specifically binds to the VgrG spike in the heterologous environment and propose that there are additional requirements to allow proper effector delivery and translocation. Our work sheds light on complex aspects of the molecular mechanisms of T6SS delivery and highlights some limitations on how effectors can be translocated using this nanomachine.

'It's our everyday life' - The perspectives of persons with intellectual disabilities in Norway.

This study illuminates how adults with intellectual disabilities understand and describe their everyday life and its shortcomings when it comes to equal rights in the context of Norwegian community living. An inclusive research design, including nine persons with mild intellectual disability, two university researchers and two intellectual disability nurses from the municipality, was undertaken. An inductive thematic analysis of data identified three key themes: everyday life - context, rhythm and structure, social participation and staff - an ambiguous part of everyday life. Results show that service provision had institutional qualities; participants experienced lack of information and reduced possibilities for social inclusion and community participation like everyone else. More attention on the role of policy development, support staff and leadership, in relation to facilitating an everyday life with more user involvement, social inclusion and community participation of people needing support, is essential. Participatory, appreciative, action and reflection in workshops for persons with intellectual disabilities and support staff represent a promising approach to promote the voices and interests of persons with intellectual disabilities. This article tells you about the everyday life of people with intellectual disabilities living in Norway. Nine people with intellectual disabilities worked together with two university researchers and two intellectual disability nurses in the community, in workshops. The people with intellectual disabilities liked to have their own apartment and going to work every day. They said that they wanted more social participation with friends and more participation in activities in the community, just like everyone else. They wanted to be treated with more respect by their staff. All participants in the project saw great value in working together and some of them are working together in a new project about involvement in the improvement of support services for people with intellectual disabilities.

Bioinformatic Analysis of the Type VI Secretion System and Its Potential Toxins in the Acinetobacter Genus.

Several Acinetobacter strains are important nosocomial pathogens, with Acinetobacter baumannii as the species of greatest concern worldwide due to its multi-drug resistance and recent appearance of hyper-virulent strains in the clinical setting. Acinetobacter colonization of the environment and the host is associated with a multitude of factors which remain poorly characterized. Among them, the secretion systems (SS) encoded by Acinetobacter species confer adaptive advantages depending on the niche occupied. Different SS have been characterized in this group of microorganisms, including T6SS used by several Acinetobacter species to outcompete other bacteria and in some A. baumannii strains for Galleria mellonella colonization. Therefore, to better understand the distribution of the T6SS in this genus we carried out an in-depth comparative genomic analysis of the T6SS in 191 sequenced strains. To this end, we analyzed the gene content, sequence similarity, synteny and operon structure of each T6SS loci. The presence of a single conserved T6SS-main cluster (T6SS-1), with two different genetic organizations, was detected in the genomes of several ecologically diverse species. Furthermore, a second main cluster (T6SS-2) was detected in a subgroup of 3 species of environmental origin. Detailed analysis also showed an impressive genetic versatility in T6SS-associated islands, carrying VgrG, PAAR and putative toxin-encoding genes. This in silico study represents the first detailed intra-species comparative analysis of T6SS-associated genes in the Acinetobacter genus, that should contribute to the future experimental characterization of T6SS proteins and effectors.

PAAR proteins act as the 'sorting hat' of the type VI secretion system.

Bacteria exist in polymicrobial environments and compete to prevail in a niche. The type VI secretion system (T6SS) is a nanomachine employed by Gram-negative bacteria to deliver effector proteins into target cells. Consequently, T6SS-positive bacteria produce a wealth of antibacterial effector proteins to promote their survival among a prokaryotic community. These toxins are loaded onto the VgrG-PAAR spike and Hcp tube of the T6SS apparatus and recent work has started to document the specificity of effectors for certain spike components. Pseudomonas aeruginosa encodes several PAAR proteins, whose roles have been poorly investigated. Here we describe a phospholipase family antibacterial effector immunity pair from Pseudomonas aeruginosa and demonstrate that a specific PAAR protein is necessary for the delivery of the effector and its cognate VgrG. Furthermore, the PAAR protein appears to restrict the delivery of other phospholipase effectors that utilise distinct VgrG proteins. We provide further evidence for competition for PAAR protein recruitment to the T6SS apparatus, which determines the identities of the delivered effectors.

The Pseudomonas aeruginosa T6SS-VgrG1b spike is topped by a PAAR protein eliciting DNA damage to bacterial competitors.

The type VI secretion system (T6SS) is a supramolecular complex involved in the delivery of potent toxins during bacterial competition. Pseudomonas aeruginosa possesses three T6SS gene clusters and several hcp and vgrG gene islands, the latter encoding the spike at the T6SS tip. The vgrG1b cluster encompasses seven genes whose organization and sequences are highly conserved in P. aeruginosa genomes, except for two genes that we called tse7 and tsi7 We show that Tse7 is a Tox-GHH2 domain nuclease which is distinct from other T6SS nucleases identified thus far. Expression of this toxin induces the SOS response, causes growth arrest and ultimately results in DNA degradation. The cytotoxic domain of Tse7 lies at its C terminus, while the N terminus is a predicted PAAR domain. We find that Tse7 sits on the tip of the VgrG1b spike and that specific residues at the PAAR-VgrG1b interface are essential for VgrG1b-dependent delivery of Tse7 into bacterial prey. We also show that the delivery of Tse7 is dependent on the H1-T6SS cluster, and injection of the nuclease into bacterial competitors is deployed for interbacterial competition. Tsi7, the cognate immunity protein, protects the producer from the deleterious effect of Tse7 through a direct protein-protein interaction so specific that toxin/immunity pairs are effective only if they originate from the same P. aeruginosa isolate. Overall, our study highlights the diversity of T6SS effectors, the exquisite fitting of toxins on the tip of the T6SS, and the specificity in Tsi7-dependent protection, suggesting a role in interstrain competition.

Comparative Evaluation of the Viscosity and Length of Resin Tags of Conventional and Hydrophilic Pit and Fissure Sealants on Permanent Molars: An In vitro Study.

BACKGROUND: The World Health Organization considers sealing the pit and fissures as a primary preventive measure and is one of the most effective, least invasive means to ensure the complete protection of the occlusal surface from the carious phenomenon. In vitro tests play a vital role in providing the necessary information regarding the efficacy of newer brands of sealants in a short period. Therefore, the aim of the present study was to evaluate and compare the viscosity and length of resin tag of conventional and hydrophilic sealant on permanent molars. MATERIALS AND METHODS: Twenty extracted third molars were randomly divided into two groups: Group I: Conventional sealant (Clinpro 3M ESPE) and Group II: Hydrophilic sealant (UltraSeal XT Hydro). Occlusal surfaces of each tooth were pretreated with the acid etchant, and the respective sealants were placed. Both the groups were then subjected to thermocycling and sectioned longitudinally. The sectioned tooth specimens were examined under scanning electron microscope for resin tag length measurements. Viscosities were evaluated using an Anton Paar viscometer. Independent t-test was used to compare the difference in mean resin tag length of Group I and Group II sealants. RESULTS: Viscosity measurements of Group I and Group II were found to be 0.9 mega Pascal (MPa) and 0.7 MPa and the mean resin tag length of Group II (10.03 ± 1.00 µm) was found to be higher than Group I (7.46 ± 0.95 µm) and was found to be significant statistically (P = 0.001). CONCLUSION: Based on the results of the present study, it can be concluded that Group II sealant exhibited lower viscosity and formed resin tag of sufficient length than that of Group I sealants. Therefore, hydrophilic sealant showed better results as compared to a conventional sealant.

Francisella IglG protein and the DUF4280 proteins: PAAR-like proteins in non-canonical Type VI secretion systems?

Type VI secretion systems (T6SS) are bacterial molecular machines translocating effector proteins into target cells. T6SS are widely present in Gram-negative bacteria where they predominantly act to kill neighboring bacteria. This secretion system is reminiscent of the tail of contractile bacteriophages and consists of a contractile sheath anchored in the bacterial envelope and an inner tube made of stacks of the Hcp protein. The Hcp tube is capped with a VgrG trimer and a spike protein termed PAAR, which acts as the membrane-puncturing device. Francisella tularensis, the agent of tularemia, is an intracellular bacterium replicating within the host cytosol. Upon entry into the host cell, F. tularensis rapidly lyses the host vacuolar membrane to reach the host cytosol. This escape is dependent on the Francisella Pathogenicity Island (FPI), which is encoding an atypical T6SS. Among the 17 proteins encoded by the FPI, most of them required for virulence, eight have some homology to canonical T6SS proteins. We recently identified the function of one protein of unknown function encoded within the FPI, IglG. By three-dimensional modelling and following validation by different techniques, we found that IglG adopts a fold resembling the one of PAAR proteins. Importantly, IglG features a domain of unknown function DUF4280, present in numerous bacterial species. We thus propose to rename this domain of unknown function, PAAR-like domain, and discuss here the characteristics of this domain and its distribution in both Gram-negative and Gram-positive bacteria.