Levels of sCD163 in women rheumatoid arthritis: Relationship with cardiovascular risk markers.

AIM: The soluble scavenger receptor differentiation antigen 163 (sCD163), a monocyte/macrophage activation marker, is related to cardiovascular mortality in the general population. This study aimed to evaluate their relationship between serum levels of sCD163 with cardiovascular risk indicators in rheumatoid arthritis (RA). METHODS: A cross-sectional study was performed on 80 women diagnosed with RA. The cardiovascular risks were determined using the lipid profile, metabolic syndrome, and QRISK3 calculator. For the assessment of RA activity, we evaluated the DAS28 with erythrocyte sedimentation rate (DAS28-ESR). The serum levels of sCD163 were determined by the ELISA method. Logistic regression models and receiver operating characteristics (ROC) curve were used to assess the association and predictive value of sCD163 with cardiovascular risk in RA patients. RESULTS: Levels of sCD163 were significantly higher in RA patients with high sensitivity protein C-reactive to HDL-c ratio (CHR)≥0.121 (p=0.003), total cholesterol/HDL-c ratio>7% (p=0.004), LDL-c/HDL-c ratio>3% (p=0.035), atherogenic index of plasma>0.21 (p=0.004), cardiometabolic index (CMI)≥1.70 (p=0.005), and high DAS28-ESR (p=0.004). In multivariate analysis, levels of sCD163≥1107.3ng/mL were associated with CHR≥0.121 (OR=3.43, p=0.020), CMI≥1.70 (OR=4.25, p=0.005), total cholesterol/HDL-c ratio>7% (OR=6.63, p=0.044), as well as with DAS28-ESR>3.2 (OR=8.10, p=0.008). Moreover, levels of sCD163 predicted CHR≥0.121 (AUC=0.701), cholesterol total/HDL ratio>7% (AUC=0.764), and DAS28-ESR>3.2 (AUC=0.720). CONCLUSION: Serum levels of sCD163 could be considered a surrogate of cardiovascular risk and clinical activity in RA.

Combined effect of SAR-endolysin LysKpV475 with polymyxin B and Salmonella bacteriophage phSE-5.

Endolysins are bacteriophage (or phage)-encoded enzymes that catalyse the peptidoglycan breakdown in the bacterial cell wall. The exogenous action of recombinant phage endolysins against Gram-positive organisms has been extensively studied. However, the outer membrane acts as a physical barrier when considering the use of recombinant endolysins to combat Gram-negative bacteria. This study aimed to evaluate the antimicrobial activity of the SAR-endolysin LysKpV475 against Gram-negative bacteria as single or combined therapies, using an outer membrane permeabilizer (polymyxin B) and a phage, free or immobilized in a pullulan matrix. In the first step, the endolysin LysKpV475 in solution, alone and combined with polymyxin B, was tested in vitro and in vivo against ten Gram-negative bacteria, including highly virulent strains and multidrug-resistant isolates. In the second step, the lyophilized LysKpV475 endolysin was combined with the phage phSE-5 and investigated, free or immobilized in a pullulan matrix, against Salmonella enterica subsp. enterica serovar Typhimurium ATCC 13311. The bacteriostatic action of purified LysKpV475 varied between 8.125 µg ml-1 against Pseudomonas aeruginosa ATCC 27853, 16.25 µg ml-1 against S. enterica Typhimurium ATCC 13311, and 32.50 µg ml-1 against Klebsiella pneumoniae ATCC BAA-2146 and Enterobacter cloacae P2224. LysKpV475 showed bactericidal activity only for P. aeruginosa ATCC 27853 (32.50 µg ml-1) and P. aeruginosa P2307 (65.00 µg ml-1) at the tested concentrations. The effect of the LysKpV475 combined with polymyxin B increased against K. pneumoniae ATCC BAA-2146 [fractional inhibitory concentration index (FICI) 0.34; a value lower than 1.0 indicates an additive/combined effect] and S. enterica Typhimurium ATCC 13311 (FICI 0.93). A synergistic effect against S. enterica Typhimurium was also observed when the lyophilized LysKpV475 at ⅔ MIC was combined with the phage phSE-5 (m.o.i. of 100). The lyophilized LysKpV475 immobilized in a pullulan matrix maintained a significant Salmonella reduction of 2 logs after 6 h of treatment. These results demonstrate the potential of SAR-endolysins, alone or in combination with other treatments, in the free form or immobilized in solid matrices, which paves the way for their application in different areas, such as in biocontrol at the food processing stage, biosanitation of food contact surfaces and biopreservation of processed food in active food packing.

Impacto del consumo de frutas y verduras en el riesgo de desarrollo de la preeclampsia: una revisión sistemática

Introducción: La preeclampsia es una afectación multisistémica que contribuye a la morbilidad y mortalidad materna junto con importantes complicaciones fetales. Dado que se ha observado que el consumo de frutas y vegetales posee un efecto beneficioso en la reducción del riesgo de enfermedades cardiovasculares, el consumo de estos alimentos también podría reducir el riesgo de desarrollo de preeclampsia en la mujer embarazada. Objetivo: Analizar el impacto del consumo de frutas y vegetales en el riesgo de desarrollo de preeclampsia en la mujer embarazada. Metodología: Se ha realizado una revisión sistemática siguiendo la metodología PRISMA. Las bases de datos utilizadas fueron Scopus, Pubmed y Web of Science. Se han incluido artículos publicados en los últimos cinco años, escritos en inglés o español y de acceso gratuito. La calidad metodológica se evaluó mediante la escala de STROBE y MINCIR. Resultados: Se han seleccionado nueve artículos para dar respuesta al objetivo planteado. El porcentaje de gestantes con un patrón dietético basado en frutas y vegetales que desarrolla preeclampsia es relativamente bajo, oscilando entre el 7 y el 8,8%. Así mismo, la mayoría de los estudios seleccionados muestran que la ingesta de frutas y vegetales tiene un efecto protector en el desarrollo de preeclampsia y, que este efecto protector es directamente proporcional al número de raciones consumidas de estos alimentos. Conclusiones: La literatura disponible para analizar el impacto que tiene el consumo de frutas y vegetales en el riesgo de desarrollo de preeclampsia es muy limitada. Por ello, se insta a realizar más investigaciones sobre este tema para poder aportar unos resultados más robustos.

Introduction: Preeclampsia is a multisystem affectation that contributes to maternal morbidity and mortality along with important fetal complications. Since it has been observed that the consumption of fruits and vegetables has a beneficial effect in reducing the risk of cardiovascular diseases, the consumption of these foods could also reduce the risk and development of preeclampsia in pregnant women. Objective: To analyze the impact of fruit and vegetable consumption on the risk of development of preeclampsia in pregnant women. Methodology: A systematic review has been carried out following the PRISMA methodology. The databases used were Scopus, Pubmed and Web of Science. Articles published in the last five years, written in English or Spanish and with free access have been included. Methodological quality was assessed using the STROBE and MINCIR scales. Results: There have been selected nine articles to provide a response to the proposed objective. The percentage of pregnant women with a dietary pattern based on fruits and vegetables who develop preeclampsia is relatively low, ranging between 7 and 8.8%. Likewise, most of the selected studies show that the intake of fruits and vegetables has a protective effect on the development of preeclampsia and that this protective effect is directly proportional to the number of servings consumed of these foods. Conclusions: The literature available to analyze the impact that fruit and vegetable consumption has on the risk and development of preeclampsia is very limited. Therefore, more research on this topic is urged to provide more robust results.

Enhanced degradation of ciprofloxacin in water using ternary photocatalysts TiO2/SnO2/g-C3N4 under UV, visible, and solar light.

In this study, we report on the synthesis of ternary photocatalysts comprising TiO2/SnO2/g-C3N4 for the degradation of ciprofloxacin (CIP) in water. SnO2 nanoparticles were synthesized via the sol-gel method, while g-C3N4 was obtained through melamine calcination. Commercial TiO2 and SnO2 nanopowders were also used. The heterojunctions were synthesized via the wet impregnation method. The photocatalysts were characterized via various techniques, including XRD, TEM, STEM, FTIR, N2 adsorption, UV-Vis DR, and hole tests. Photocatalytic degradation tests of CIP were carried out under UV, visible, and solar radiation. The P25/npA/g-C3N4 (90/10) material exhibited the best performance, achieving CIP degradation of over 97%. The synthesized materials demonstrated excellent initial adsorption of CIP, around 30%, which facilitated subsequent degradation. Notably, the CIP photocatalytic degradation tests performed under solar radiation showed a synergistic effect between the base materials and carbon nitride in highly energetic environments. These results highlight the effectiveness of ternary photocatalysts TiO2/SnO2/g-C3N4 for CIP degradation, particularly under solar radiation.

The AraC-type transcription factor TagK is a new player in the signaling cascade that induces the anti-eukaryotic T6SS of Xanthomonas citri.

Type 6 secretion systems (T6SSs) are specialized multiprotein complexes that inject protein effectors into prokaryotic and/or eukaryotic cells. We previously described the role of the T6SS of the phytopathogen Xanthomonas citri pv. citri as an anti-eukaryotic nanoweapon that confers resistance to predation by the amoeba Dictyostelium discoideum. Transcription of the X. citri T6SS genes is induced by a signaling cascade involving the Ser/Thr kinase PknS and the extracytoplasmic function sigma factor EcfK. Here, we used a strain overexpressing a phosphomimetic constitutively active version of EcfK (EcfKT51E ) to identify the EcfK regulon, which includes a previously uncharacterized transcription factor of the AraC-family (TagK), in addition to T6SS genes and genes encoding protein homeostasis factors. Functional studies demonstrated that TagK acts downstream of EcfK, binding directly to T6SS gene promoters and inducing T6SS expression in response to contact with amoeba cells. TagK controls a small regulon, consisting of the complete T6SS, its accessory genes and additional genes encoded within the T6SS cluster. We conclude that a singular regulatory circuit consisting of a transmembrane kinase (PknS), an alternative sigma factor (EcfK) and an AraC-type transcriptional regulator (TagK) promotes expression of the X. citri T6SS in response to a protozoan predator.

An Extracytoplasmic Function Sigma Factor Required for Full Virulence in Xanthomonas citri pv. citri.

The genus Xanthomonas includes more than 30 phytopathogenic species that infect a wide range of plants and cause severe diseases that greatly impact crop productivity. These bacteria are highly adapted to the soil and plant environment, being found in decaying material, as epiphytes, and colonizing the plant mesophyll. Signal transduction mechanisms involved in the responses of Xanthomonas to environmental changes are still poorly characterized. Xanthomonad genomes typically encode several representatives of the extracytoplasmic function σ (σECF) factors, whose physiological roles remain elusive. In this work, we functionally characterized the Xanthomonas citri pv. citri EcfL, a σECF factor homologous to members of the iron-responsive FecI-like group. We show that EcfL is not required or induced during iron starvation, despite presenting the common features of other FecI-like σECF factors. EcfL positively regulates one operon composed of three genes that encode a TonB-dependent receptor involved in cell surface signaling, an acid phosphatase, and a lectin-domain containing protein. Furthermore, we demonstrate that EcfL is required for full virulence in citrus, and its regulon is induced inside the plant mesophyll and in response to acid stress. Together, our study suggests a role for EcfL in the adaptation of X. citri to the plant environment, in this way contributing to its ability to cause citrus canker disease. IMPORTANCE The Xanthomonas genus comprises a large number of phytopathogenic species that infect a wide variety of economically important plants worldwide. Bacterial adaptation to the plant and soil environment relies on their repertoire of signal transduction pathways, including alternative sigma factors of the extracytoplasmic function family (σECF). Here, we describe a new σECF factor found in several Xanthomonas species, demonstrating its role in Xanthomonas citri virulence to citrus plants. We show that EcfL regulates a single operon containing three genes, which are also conserved in other Xanthomonas species. This study further expands our knowledge on the functions of the widespread family of σECF factors in phytopathogenic bacteria.

MutSα mismatch repair protein stability is governed by subunit interaction, acetylation, and ubiquitination.

In eukaryotes, DNA mismatch recognition is accomplished by the highly conserved MutSα (Msh2/Msh6) and MutSß (Msh2/Msh3) complexes. Previously, in the yeast Saccharomyces cerevisiae, we determined that deleting MSH6 caused wild-type Msh2 levels to drop by ∼50%. In this work, we determined that Msh6 steady-state levels are coupled to increasing or decreasing levels of Msh2. Although Msh6 and Msh2 are reciprocally regulated, Msh3 and Msh2 are not. Msh2 missense variants that are able to interact with Msh6 were destabilized when Msh6 was deleted; in contrast, variants that fail to dimerize were not further destabilized in cells lacking Msh6. In the absence of Msh6, Msh2 is turned over at a faster rate and degradation is mediated by the ubiquitin-proteasome pathway. Mutagenesis of certain conserved lysines near the dimer interface restored the levels of Msh2 in the absence of Msh6, further supporting a dimer stabilization mechanism. We identified two alternative forms of regulation both with the potential to act via lysine residues, including acetylation by Gcn5 and ubiquitination by the Not4 ligase. In the absence of Gcn5, Msh2 levels were significantly decreased; in contrast, deleting Not4 stabilized Msh2 and Msh2 missense variants with partial function. The stabilizing effect on Msh2 by either the presence of Msh6 or the absence of Not4 are dependent on Gcn5. Taken together, the results suggest that the wild-type MutSα mismatch repair protein stability is governed by subunit interaction, acetylation, and ubiquitination.

Secrete or perish: The role of secretion systems in Xanthomonas biology.

Bacteria of the Xanthomonas genus are mainly phytopathogens of a large variety of crops of economic importance worldwide. Xanthomonas spp. rely on an arsenal of protein effectors, toxins and adhesins to adapt to the environment, compete with other microorganisms and colonize plant hosts, often causing disease. These protein effectors are mainly delivered to their targets by the action of bacterial secretion systems, dedicated multiprotein complexes that translocate proteins to the extracellular environment or directly into eukaryotic and prokaryotic cells. Type I to type VI secretion systems have been identified in Xanthomonas genomes. Recent studies have unravelled the diverse roles played by the distinct types of secretion systems in adaptation and virulence in xanthomonads, unveiling new aspects of their biology. In addition, genome sequence information from a wide range of Xanthomonas species and pathovars have become available recently, uncovering a heterogeneous distribution of the distinct families of secretion systems within the genus. In this review, we describe the architecture and mode of action of bacterial type I to type VI secretion systems and the distribution and functions associated with these important nanoweapons within the Xanthomonas genus.

Gaining insight into the implementation of an e-learning smoking cessation course in Latin American countries.

Continuous medical education focused on health problems emerging in low- and middle-income countries (LMICs) is scarce. Although tobacco consumption is increasing in LMICs, there is a lack of tobacco cessation training programs in these countries. To promote smoking cessation interventions in Bolivia, Guatemala and Paraguay, we adapted an e-learning program developed in Catalonia (Spain). This process evaluation study reports on reach, dose and satisfaction of participants with the course, as well as the contextual factors of its application. We conducted a multiple method evaluation, which included a survey and several focus groups, each one specific to the same type of healthcare professional (nurses, doctors, other professionals). Two hundred and ninety-two participants registered into the online course. The motivation for undertaking the course was different between doctors and nurses. The main sources of difficulty in enrolling and finishing the course were the technical problems experienced when accessing the platform, and lack of acquaintance with computers and the Internet in general. Our results show that implementing e-learning education in hospitals from LMICs is feasible, especially when there are similarities between participating countries and the country in which the original program was developed. However, several elements such as strong organizational commitment, technical support and resources and adequate communication channels should be provided to facilitate enrollment and training completion. Efforts to improve Internet access should be made to avoid jeopardizing students' motivation to enroll and complete online training.

First Clinical Application of Polyurethane Meniscal Scaffolds with Mesenchymal Stem Cells and Assessment of Cartilage Quality with T2 Mapping at 12 Months.

BACKGROUND: Complex meniscal lesions often require meniscectomy with favorable results in the short term but a high risk of early osteoarthritis subsequently. Partial meniscectomy treated with meniscal substitutes may delay articular cartilage degeneration. PURPOSE: To evaluate the status of articular cartilage by T2 mapping after meniscal substitution with polyurethane scaffolds enriched with mesenchymal stem cells (MSC) and comparison with acellular scaffolds at 12 months. METHODS: Seventeen patients (18-50 years) with past meniscectomies were enrolled in 2 groups: (1) acellular polyurethane scaffold (APS) or (2) polyurethane scaffold enriched with MSC (MPS). Patients in the MPS group received filgrastim to stimulate MSC production, and CD90+ cells were obtained and cultured in the polyurethane scaffold. The scaffolds were implanted arthroscopically into partial meniscus defects. Concomitant injuries (articular cartilage lesions or cartilage lesions) were treated during the same procedure. Changes in the quality of articular cartilage were evaluated with T2 mapping in femur and tibia at 12 months. RESULTS: In tibial T2 mapping, values for the MPS group increased slightly at 9 months but returned to initial values at 12 months (P > 0.05). In the APS group, a clear decrease from 3 months to 12 months was observed (P > 0.05). This difference tended to be significantly lower in the APS group compared with the MPS group at the final time point (P = 0.18). In the femur, a slight increase in the MPS group (47.8 ± 3.4) compared with the APS group (45.3 ± 4.9) was observed (P > 0.05). CONCLUSION: Meniscal substitution with polyurethane scaffold maintains normal T2 mapping values in adjacent cartilage at 12 months. The addition of MSC did not show any advantage in the protection of articular cartilage over acellular scaffolds (P > 0.05).

Boar seminal plasma: current insights on its potential role for assisted reproductive technologies in swine.

Seminal plasma (SP) supports not only sperm function but also the ability of spermatozoa to withstand biotechnological procedures as artificial insemination, freezing or sex sorting. Moreover, evidence has been provided that SP contains identifiable molecules which can act as fertility biomarkers, and even improve the output of assisted reproductive technologies by acting as modulators of endometrial and embryonic changes of gene expression, thus affecting embryo development and fertility beyond the sperm horizon. In this overview, we discuss current knowledge of the composition of SP, mainly proteins and cytokines, and their influence on semen basic procedures, such as liquid storage or cryopreservation. The role of SP as modulator of endometrial and embryonic molecular changes that lead to successful pregnancy will also be discussed.

Bactericidal type IV secretion system homeostasis in Xanthomonas citri.

Several Xanthomonas species have a type IV secretion system (T4SS) that injects a cocktail of antibacterial proteins into neighbouring Gram-negative bacteria, often leading to rapid lysis upon cell contact. This capability represents an obvious fitness benefit since it can eliminate competition while the liberated contents of the lysed bacteria could provide an increase in the local availability of nutrients. However, the production of this Mega Dalton-sized molecular machine, with over a hundred subunits, also imposes a significant metabolic cost. Here we show that the chromosomal virB operon, which encodes the structural genes of this T4SS in X. citri, is regulated by the conserved global regulator CsrA. Relieving CsrA repression from the virB operon produced a greater number of T4SSs in the cell envelope and an increased efficiency in contact-dependent lysis of target cells. However, this was also accompanied by a physiological cost leading to reduced fitness when in co-culture with wild-type X. citri. We show that T4SS production is constitutive despite being downregulated by CsrA. Cells subjected to a wide range of rich and poor growth conditions maintain a constant density of T4SSs in the cell envelope and concomitant interbacterial competitiveness. These results show that CsrA provides a constant though partial repression on the virB operon, independent of the tested growth conditions, in this way controlling T4SS-related costs while at the same time maintaining X. citri's aggressive posture when confronted by competitors.

Sterilized chitosan-based composite hydrogels: Physicochemical characterization and in vitro cytotoxicity.

Gelatin/chitosan/polyvinyl alcohol hydrogels were fabricated at different polymer ratios using the freeze-drying and sterilized by steam sterilization. The thermal stability, chemical structure, morphology, surface area, mechanical properties, and biocompatibility of hydrogels were evaluated by simultaneous thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction, confocal microscopy, adsorption/desorption of nitrogen, rheometry, and 3-4,[5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide cell viability assay (MTT assay), respectively. The samples showed a decomposition onset temperature below 253.3 ± 4.8°C, a semicrystalline nature, and a highly porous structure. Hydrogels reached the maximum water uptake in phosphate-buffered saline after 80 min, showing values from nine to twelve times their dry mass. Also, hydrogels exhibiting a solid-like behavior ranging from 2,567 ± 467 to 48,705 ± 2,453 Pa at 0.1 rad/s (low frequency). The sterilized hydrogels showed low cytotoxicity (cell viability > 70%) to the HT29-MTX-E12 cell line. Sterilized hydrogels by steam sterilization can be good candidates as scaffolds for tissue engineering applications.

Boar seminal plasma: current insights on its potential role for assisted reproductive technologies in swine

Seminal plasma (SP) supports not only sperm function but also the ability of spermatozoa to withstand biotechnological procedures as artificial insemination, freezing or sex sorting. Moreover, evidence has been provided that SP contains identifiable molecules which can act as fertility biomarkers, and even improve the output of assisted reproductive technologies by acting as modulators of endometrial and embryonic changes of gene expression, thus affecting embryo development and fertility beyond the sperm horizon. In this overview, we discuss current knowledge of the composition of SP, mainly proteins and cytokines, and their influence on semen basic procedures, such as liquid storage or cryopreservation. The role of SP as modulator of endometrial and embryonic molecular changes that lead to successful pregnancy will also be discussed.(AU)

Boar seminal plasma: current insights on its potential role for assisted reproductive technologies in swine

Seminal plasma (SP) supports not only sperm function but also the ability of spermatozoa to withstand biotechnological procedures as artificial insemination, freezing or sex sorting. Moreover, evidence has been provided that SP contains identifiable molecules which can act as fertility biomarkers, and even improve the output of assisted reproductive technologies by acting as modulators of endometrial and embryonic changes of gene expression, thus affecting embryo development and fertility beyond the sperm horizon. In this overview, we discuss current knowledge of the composition of SP, mainly proteins and cytokines, and their influence on semen basic procedures, such as liquid storage or cryopreservation. The role of SP as modulator of endometrial and embryonic molecular changes that lead to successful pregnancy will also be discussed.

Gastric duplication cyst in the adult. A case report.

Gastric duplication cyst is a very rare congenital anomaly accounting up to 4-9% of all gastrointestinal tract duplications. It is a quite rare anomaly in adults, the majority of cases are diagnosed in the neonatal period. Gastric duplication cysts are usually asymptomatic in the adult. They are usually discovered incidentally in TAC or RMN, although the best specificity diagnostic test is the echoendoscopy. The best election treatment is the surgical complete extirpation. We describe a case of an adult patient who is diagnosed of the incidentally gastric cyst duplication.

El quiste de duplicación gástrico es una anomalía congénita muy rara que representa entre 4 y 9% de todas las duplicaciones del aparato digestivo. Es una alteración bastante rara en el adulto y la mayoría de los casos se diagnostica en el periodo neonatal. En el adulto suele cursar de forma asintomática y la TC o RMN la descubren de forma incidental, aunque la prueba que la diagnóstica con mayor eficacia es la ecoendoscopia. La extirpación quirúrgica completa de la lesión se considera el tratamiento de elección. Se presenta el caso clínico de una paciente con un quiste de duplicación gástrico diagnosticado de forma incidental.

Distribution, Function and Regulation of Type 6 Secretion Systems of Xanthomonadales.

Members of the Xanthomonadales order include several plant pathogens of significant economic and agricultural impact, such as Xanthomonas spp. Type 6 secretion systems (T6SSs) are contractile nanomachines used by many bacterial species to inject protein effectors into target prokaryotic and eukaryotic cells and provide a competitive advantage for bacteria in different environments. Effectors with antibacterial properties include peptidoglycan hydrolases, lipases and phospholipases that break down structural components of the cell envelope, promoting target-cell lysis; and RNases, DNAses, and NADases that affect target-cell metabolism, arresting growth. Effectors with anti-eukaryotic properties are functionally more diverse. The T6SS of Xanthomonas citri is the only example experimentally characterized so far within the Xanthomonadales order and displays anti-eukaryotic function by providing resistance to predation by amoeba. This T6SS is regulated at the transcriptional level by a signaling cascade involving a Ser/Thr kinase and an extracytoplasmic function (ECF) sigma factor. In this review, we performed in silico analyses of 35 genomes of Xanthomonadales and showed that T6SSs are widely distributed and phylogenetically classified into three major groups. In silico predictions identified a series of proteins with known toxic domains as putative T6SS effectors, suggesting that the T6SSs of Xanthomonadales display both anti-prokaryotic and anti-eukaryotic properties depending on the phylogenetic group and bacterial species.

The Xanthomonas citri pv. citri Type VI Secretion System is Induced During Epiphytic Colonization of Citrus.

Xanthomonas citri pv. citri (X. citri pv. citri) is the causal agent of Asiatic citrus canker and infects economically important citrus crops. X. citri pv. citri contains one type VI secretion system (T6SS) required for resistance to predation by the soil amoeba Dictyostelium discoideum and induced by the ECF sigma factor EcfK in the presence of amoeba. In this work, we describe the analysis of T6SS gene expression during interaction with host plants. We show that T6SS genes and the cognate positive regulator ecfK are upregulated during growth in the plant surface (epiphytic) and maintain low expression levels during growth inside plant mesophyll. In addition, expression of the virulence-associated T3SS is also induced during epiphytic growth and shows a temporal induction pattern during growth inside plant leaves. The T6SS is not required for adhesion to leaf surface and biofilm formation during the first stages of plant colonization nor for killing of yeasts cells. Since the phyllosphere is colonized by eukaryotic predators of bacteria, induction of the X. citri pv. citri anti-amoeba T6SS during epiphytic growth suggests the presence of an environmental signal that triggers the resistance phenotype.

Bacteria-Killing Type IV Secretion Systems.

Bacteria have been constantly competing for nutrients and space for billions of years. During this time, they have evolved many different molecular mechanisms by which to secrete proteinaceous effectors in order to manipulate and often kill rival bacterial and eukaryotic cells. These processes often employ large multimeric transmembrane nanomachines that have been classified as types I-IX secretion systems. One of the most evolutionarily versatile are the Type IV secretion systems (T4SSs), which have been shown to be able to secrete macromolecules directly into both eukaryotic and prokaryotic cells. Until recently, examples of T4SS-mediated macromolecule transfer from one bacterium to another was restricted to protein-DNA complexes during bacterial conjugation. This view changed when it was shown by our group that many Xanthomonas species carry a T4SS that is specialized to transfer toxic bacterial effectors into rival bacterial cells, resulting in cell death. This review will focus on this special subtype of T4SS by describing its distinguishing features, similar systems in other proteobacterial genomes, and the nature of the effectors secreted by these systems and their cognate inhibitors.