RESUMEN

In many bacteria, the BarA/SirA and Csr regulatory systems control expression of genes encoding a wide variety of cellular functions. The BarA/SirA two-component system induces the expression of CsrB and CsrC, two small non-coding RNAs that sequester CsrA, a protein that binds to target mRNAs and thus negatively or positively regulates their expression. BarA/SirA and CsrB/C induce expression of the Salmonella Pathogenicity Island 1 (SPI-1) genes required for Salmonella invasion of host cells. To further investigate the regulatory role of the BarA/SirA and Csr systems in Salmonella, we performed LC-MS/MS proteomic analysis using the WT S. Typhimurium strain and its derived ΔsirA and ΔcsrB ΔcsrC mutants grown in SPI-1-inducing conditions. The expression of 164 proteins with a wide diversity, or unknown, functions was significantly affected positively or negatively by the absence of SirA and/or CsrB/C. Interestingly, 19 proteins were identified as new targets for SirA-CsrB/C. Our results support that SirA and CsrB/C act in a cascade fashion to regulate gene expression in S. Typhimurium in the conditions tested. Notably, our results show that SirA-CsrB/C-CsrA controls expression of proteins required for the replication of Salmonella in the intestinal lumen, in an opposite way to its control exerted on the SPI-1 proteins. SIGNIFICANCE: The BarA/SirA and Csr global regulatory systems control a wide range of cellular processes, including the expression of virulence genes. For instance, in Salmonella, BarA/SirA and CsrB/C positively regulate expression of the SPI-1 genes, which are required for Salmonella invasion to host cells. In this study, by performing a proteomic analysis, we identified 164 proteins whose expression was positively or negatively controlled by SirA and CsrB/C in SPI-1-inducing conditions, including 19 new possible targets of these systems. Our results support the action of SirA and CsrB/C in a cascade fashion to control different cellular processes in Salmonella. Interestingly, our data indicate that SirA-CsrB/C-CsrA controls inversely the expression of proteins required for invasion of the intestinal epithelium and for replication in the intestinal lumen, which suggests a role for this regulatory cascade as a molecular switch for Salmonella virulence. Thus, our study further expands the insight into the regulatory mechanisms governing the virulence and physiology of an important pathogen.

Asunto(s)

Salmonella typhimurium , Transactivadores , Salmonella typhimurium/genética , Transactivadores/metabolismo , Cromatografía Liquida , Proteómica , Espectrometría de Masas en Tándem , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Regulación Bacteriana de la Expresión Génica

RESUMEN

[This corrects the article DOI: 10.3389/fmicb.2022.845473.].

RESUMEN

Alginates are a family of polymers composed of guluronate and mannuronate monomers joined by ß (1-4) links. The different types of alginates have variations in their monomer content and molecular weight, which determine the rheological properties and their applications. In industry, alginates are commonly used as additives capable of viscosifying, stabilizing, emulsifying, and gelling aqueous solutions. Recently, additional specialized biomedical uses have been reported for this polymer. Currently, the production of alginates is based on the harvesting of seaweeds; however, the composition and structure of the extracts are highly variable. The production of alginates for specialized applications requires a precise composition of monomers and molecular weight, which could be achieved using bacterial production systems such as those based on Azotobacter vinelandii, a free-living, non-pathogenic bacterium. In this mini-review, we analyze the latest advances in the regulation of alginate synthesis in this model.

RESUMEN

Azotobacter vinelandii produces the linear exopolysaccharide alginate, a compound of significant biotechnological importance. The biosynthesis of alginate in A. vinelandii and Pseudomonas aeruginosa has several similarities but is regulated somewhat differently in the two microbes. Here, we show that the second messenger cyclic dimeric GMP (c-di-GMP) regulates the production and the molecular mass of alginate in A. vinelandii The hybrid protein MucG, containing conserved GGDEF and EAL domains and N-terminal HAMP and PAS domains, behaved as a c-di-GMP phosphodiesterase (PDE). This activity was found to negatively affect the amount and molecular mass of the polysaccharide formed. On the other hand, among the diguanylate cyclases (DGCs) present in A. vinelandii, AvGReg, a globin-coupled sensor (GCS) DGC that directly binds to oxygen, was identified as the main c-di-GMP-synthesizing contributor to alginate production. Overproduction of AvGReg in the parental strain phenocopied a ΔmucG strain with regard to alginate production and the molecular mass of the polymer. MucG was previously shown to prevent the synthesis of high-molecular-mass alginates in response to reduced oxygen transfer rates (OTRs). In this work, we show that cultures exposed to reduced OTRs accumulated higher levels of c-di-GMP; this finding strongly suggests that at least one of the molecular mechanisms involved in modulation of alginate production and molecular mass by oxygen depends on a c-di-GMP signaling module that includes the PAS domain-containing PDE MucG and the GCS DGC AvGReg.IMPORTANCE c-di-GMP has been widely recognized for its essential role in the production of exopolysaccharides in bacteria, such as alginate produced by Pseudomonas and Azotobacter spp. This study reveals that the levels of c-di-GMP also affect the physical properties of alginate, favoring the production of high-molecular-mass alginates in response to lower OTRs. This finding opens up new alternatives for the design of tailor-made alginates for biotechnological applications.

Asunto(s)

Alginatos/metabolismo , Azotobacter vinelandii/metabolismo , GMP Cíclico/análogos & derivados , Polisacáridos Bacterianos/biosíntesis , Alginatos/química , Azotobacter vinelandii/enzimología , Azotobacter vinelandii/genética , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , GMP Cíclico/metabolismo , Proteínas de Escherichia coli/genética , Proteínas de Escherichia coli/metabolismo , Regulación Bacteriana de la Expresión Génica , Peso Molecular , Oxígeno/metabolismo , Hidrolasas Diéster Fosfóricas/genética , Hidrolasas Diéster Fosfóricas/metabolismo , Liasas de Fósforo-Oxígeno/genética , Liasas de Fósforo-Oxígeno/metabolismo , Polisacáridos Bacterianos/química

RESUMEN

The genus Azotobacter, belonging to the Pseudomonadaceae family, is characterized by the formation of cysts, which are metabolically dormant cells produced under adverse conditions and able to resist desiccation. Although this developmental process has served as a model for the study of cell differentiation in Gram-negative bacteria, the molecular basis of its regulation is still poorly understood. Here, we report that the ubiquitous second messenger cyclic dimeric GMP (c-di-GMP) is critical for the formation of cysts in Azotobacter vinelandii Upon encystment induction, the levels of c-di-GMP increased, reaching a peak within the first 6 h. In the absence of the diguanylate cyclase MucR, however, the levels of this second messenger remained low throughout the developmental process. A. vinelandii cysts are surrounded by two alginate layers with variable proportions of guluronic residues, which are introduced into the final alginate chain by extracellular mannuronic C-5 epimerases of the AlgE1 to AlgE7 family. Unlike in Pseudomonas aeruginosa, MucR was not required for alginate polymerization in A. vinelandii Conversely, MucR was necessary for the expression of extracellular alginate C-5 epimerases; therefore, the MucR-deficient strain produced cyst-like structures devoid of the alginate capsule and unable to resist desiccation. Expression of mucR was partially dependent on the response regulator AlgR, which binds to two sites in the mucR promoter, enhancing mucR transcription. Together, these results indicate that the developmental process of A. vinelandii is controlled through a signaling module that involves activation by the response regulator AlgR and c-di-GMP accumulation that depends on MucR.IMPORTANCEA. vinelandii has served as an experimental model for the study of the differentiation processes to form metabolically dormant cells in Gram-negative bacteria. This work identifies c-di-GMP as a critical regulator for the production of alginates with specific contents of guluronic residues that are able to structure the rigid laminated layers of the cyst envelope. Although allosteric activation of the alginate polymerase complex Alg8-Alg44 by c-di-GMP has long been recognized, our results show a previously unidentified role during the polymer modification step, controlling the expression of extracellular alginate epimerases. Our results also highlight the importance of c-di-GMP in the control of the physical properties of alginate, which ultimately determine the desiccation resistance of the differentiated cell.

Asunto(s)

Azotobacter vinelandii/enzimología , Proteínas Bacterianas/metabolismo , Carbohidrato Epimerasas/metabolismo , GMP Cíclico/análogos & derivados , Alginatos/metabolismo , Azotobacter vinelandii/genética , Azotobacter vinelandii/crecimiento & desarrollo , Azotobacter vinelandii/metabolismo , Proteínas Bacterianas/genética , Carbohidrato Epimerasas/genética , GMP Cíclico/metabolismo , Proteínas de Escherichia coli/genética , Proteínas de Escherichia coli/metabolismo , Regulación Bacteriana de la Expresión Génica , Liasas de Fósforo-Oxígeno/genética , Liasas de Fósforo-Oxígeno/metabolismo , Pseudomonas aeruginosa/enzimología , Pseudomonas aeruginosa/genética , Pseudomonas aeruginosa/metabolismo

RESUMEN

Azotobacter vineladii is a Gram-negative bacterium that produces alginate and poly-hydroxybutyrate (PHB), two polymers of biotechnological interest. This bacterium has the ability to form desiccation-resistant cysts. In the cyst the membrane phospholipids are replaced with a family of phenolic lipids called alkylresorcinols (ARs). The alginate, PHB, and ARs are controlled by the GacS/A two-component system and the small regulatory RNA (sRNA) RsmZ1, belonging to the Rsm (Csr) regulatory system. The Rsm (Csr) systems usually possess two or more sRNAs, in this regard A. vinelandii is the bacterium with the highest number of rsm-sRNAs. Originally, the presence of two sRNAs of the RsmY family (RsmY1 and RsmY2) was reported, but in a subsequent work it was suggested that they conformed to a single sRNA. In this work we provide genetic evidence confirming that rsmY1 and rsmY2 constitute a single gene. Also, it was established that rsmY mutation decreased alginate and ARs production, but did not affect the PHB synthesis. Transcriptional studies showed that rsmY has its higher expression during the stationary growth phase, and in the absence of RsmZ1, rsmY increases its transcription. Interestingly, rsmY expression was influenced by the carbon source, but its expression did not correlate with alginate production.

Asunto(s)

Alginatos/metabolismo , Azotobacter vinelandii/metabolismo , ARN Bacteriano/metabolismo , Resorcinoles/metabolismo , Azotobacter vinelandii/genética , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Regulación Bacteriana de la Expresión Génica , Hidroxibutiratos/metabolismo , Mutación , ARN Bacteriano/genética

RESUMEN

Objetivo: Caracterizar lesiones letales de línea media facial, signos y síntomas frecuentes, género y procedencia de los pacientes, histopatología e inmunohistoquímica en base a registros médicos institucionales de HEU entre 2011 y 2014.La lesión letal de línea media es un síndrome que inicialmente engloba variadas entidades: Linfomas no Hogdkin de células NK y T, Linfomas no Hogdkin de células B, enfermedades autoinmunes como la Granulomatosis con Poliangeítis, muchas causas infecciosas e idiopáticas con destrucción acelerada y catastrófica de la región nasofaríngea, senos paranasales y septum nasal. Síndromes de difícil diagnóstico con enfoques terapéuticos muy distintos. Metodología. Se realizó un estudio descriptivo, transversal, con revisión de todos los registros de biopsias realizados en el departamento de Anatomía Patológica del HEU desde el año 2011 al 2014. Cumplen criterios de inclusión, 34 casos. Resultados: Mayor prevalencia de lesiones en hombres 59 %, dentro del rango de edad de 19 a 59 años, con predomino de la región central de Honduras. Signo más frecuente: masa obstructiva. Diagnóstico más consignado fue Linfoma No Hodgkin sin especificación. Conclusión: Frecuencia de lesiones letales de la línea media es mayor en varones, procedentes en su mayoría de región central, síntoma y signo más frecuentes son masa obstructiva con ulceración y la rinorrea purulenta; la utilización de marcadores de inmunohistoquímica es deficiente para definir los casos inespecíficos de Linfoma No Hodgkin Nasales.

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Objective: To characterize lethal facial midline lesions, frequent signs and symptoms, gender and origin of the patients, histopathology and immunohistochemistry based on HEU institutional medical records between 2011 and 2014. Lethal midline injury is a syndrome that initially encompasses a variety of entities: non-Hogdkin lymphomas of NK and T cells, non-Hogdkin B-cell lymphomas, autoimmune diseases such as granulomatosis with polyangiitis, many infectious and idiopathic causes with accelerated and catastrophic destruction of the nasopharyngeal region, paranasal sinuses and nasal septum. Syndromes which are difficult to diagnose with very different therapeutic approaches.Methodology. A descriptive, crosssectional study was carried out with a review of all biopsy registries performed in the Department of Pathological Anatomy of HEU from 2011 to 2014. 34 cases meet the inclusion criteria. Results: There was a higher prevalence in men 59%, within the age range of 19 to 59 years, with predominance of the central region of Honduras. Most frequent sign: obstructive mass. Most diagnosed was Non-Hodgkin's lymphoma without specification. Conclusion: Frequency of lethal midline lesions is greater in males, mostly from the central region. The most frequent symptoms and signs are obstructive mass with ulceration and purulent rhinorrhea; the use of immunohistochemical markers is deficient to define nonspecific cases of Nasal Non-Hodgkin's Lymphoma.

Asunto(s)

Humanos , Masculino , Femenino , Recién Nacido , Lactante , Preescolar , Niño , Adolescente , Adulto , Persona de Mediana Edad , Granuloma Letal de la Línea Media/epidemiología , Linfoma no Hodgkin/diagnóstico , Linfoma no Hodgkin/epidemiología , Granulomatosis con Poliangitis/complicaciones , Granuloma Letal de la Línea Media/diagnóstico , Granuloma Letal de la Línea Media/etiología , Prevalencia , Estudios Transversales , Honduras/epidemiología

RESUMEN

Azotobacter vinelandii is a soil bacterium that undergoes differentiation to form cysts that are resistant to desiccation. Upon induction of cyst formation, the bacterium synthesizes alkylresorcinols that are present in cysts but not in vegetative cells. Alternative sigma factors play important roles in differentiation. In A. vinelandii, AlgU (sigma E) is involved in controlling the loss of flagella upon induction of encystment. We investigated the involvement of the sigma factor RpoS in cyst formation in A. vinelandii. We analysed the transcriptional regulation of the rpoS gene by PsrA, the main regulator of rpoS in Pseudomonas species, which are closely related to A. vinelandii. Inactivation of rpoS resulted in the inability to form cysts resistant to desiccation and to produce cyst-specific alkylresorcinols, whereas inactivation of psrA reduced by 50 % both production of alkylresorcinols and formation of cysts resistant to desiccation. Electrophoretic mobility shift assays revealed specific binding of PsrA to the rpoS promoter region and that inactivation of psrA reduced rpoS transcription by 60 %. These results indicate that RpoS and PsrA are involved in regulation of encystment and alkylresorcinol synthesis in A. vinelandii.

Asunto(s)

Azotobacter vinelandii/fisiología , Proteínas Bacterianas/metabolismo , Proteínas de Unión al ADN/metabolismo , Regulación Bacteriana de la Expresión Génica , Resorcinoles/metabolismo , Factor sigma/metabolismo , Factores de Transcripción/metabolismo , Azotobacter vinelandii/genética , Azotobacter vinelandii/metabolismo , Proteínas Bacterianas/genética , Proteínas de Unión al ADN/genética , Desecación , Ensayo de Cambio de Movilidad Electroforética , Factor sigma/genética , Factores de Transcripción/genética

RESUMEN

Azotobacter vinelandii is a nitrogen-fixing soil bacterium that produces the exopolysaccharide alginate. In this report we describe the isolation and characterization of A. vinelandii strain GG4, which carries an nqrE : : Tn5 mutation resulting in alginate overproduction. The nqrE gene encodes a subunit of the Na+-translocating NADH : ubiquinone oxidoreductase (Na+-NQR). As expected, Na+-NQR activity was abolished in mutant GG4. When this strain was complemented with the nqrEF genes this activity was restored and alginate production was reduced to wild-type levels. Na+-NQR may be the main sodium pump of A. vinelandii under the conditions tested ( approximately 2 mM Na+) since no Na+/H+-antiporter activity was detected. Collectively our results indicate that in A. vinelandii the lack of Na+-NQR activity caused the absence of a transmembrane Na+ gradient and an increase in alginate production.

Asunto(s)

Alginatos/metabolismo , Azotobacter vinelandii/enzimología , Regulación Bacteriana de la Expresión Génica , Quinona Reductasas/metabolismo , Sodio/metabolismo , Azotobacter vinelandii/genética , Azotobacter vinelandii/crecimiento & desarrollo , Elementos Transponibles de ADN , Mutación , Quinona Reductasas/genética , Ubiquinona

RESUMEN

The regulon of the sigma factor RpoS was defined in Geobacter sulfurreducens by using a combination of DNA microarray expression profiles and proteomics. An rpoS mutant was examined under steady-state conditions with acetate as an electron donor and fumarate as an electron acceptor and with additional transcriptional profiling using Fe(III) as an electron acceptor. Expression analysis revealed that RpoS acts as both a positive and negative regulator. Many of the RpoS-dependent genes determined play roles in energy metabolism, including the tricarboxylic acid cycle, signal transduction, transport, protein synthesis and degradation, and amino acid metabolism and transport. As expected, RpoS activated genes involved in oxidative stress resistance and adaptation to nutrient limitation. Transcription of the cytochrome c oxidase operon, necessary for G. sulfurreducens growth using oxygen as an electron acceptor, and expression of at least 13 c-type cytochromes, including one previously shown to participate in Fe(III) reduction (MacA), were RpoS dependent. Analysis of a subset of the rpoS mutant proteome indicated that 15 major protein species showed reproducible differences in abundance relative to those of the wild-type strain. Protein identification using mass spectrometry indicated that the expression of seven of these proteins correlated with the microarray data. Collectively, these results indicate that RpoS exerts global effects on G. sulfurreducens physiology and that RpoS is vital to G. sulfurreducens survival under conditions typically encountered in its native subsurface environments.

Asunto(s)

Proteínas Bacterianas/fisiología , Regulación Bacteriana de la Expresión Génica , Geobacter/química , Geobacter/genética , Análisis de Secuencia por Matrices de Oligonucleótidos , Proteoma/análisis , Regulón , Factor sigma/fisiología , Adaptación Fisiológica/genética , Aminoácidos/metabolismo , Proteínas Bacterianas/análisis , Proteínas Bacterianas/genética , Proteínas Bacterianas/aislamiento & purificación , Transporte Biológico/genética , Ciclo del Ácido Cítrico/fisiología , Citocromos/biosíntesis , Electroforesis en Gel Bidimensional , Eliminación de Gen , Geobacter/fisiología , Espectrometría de Masas , Mutagénesis Insercional , Estrés Oxidativo/genética , Biosíntesis de Proteínas , Proteoma/aislamiento & purificación , Factor sigma/genética , Transducción de Señal

RESUMEN

Azotobacter vinelandii is a soil gamma-proteobacteria that fixes nitrogen and forms desiccation-resistant cysts. The exopolysaccharide alginate is an integral part of the layers surrounding the cysts. Here, we reported the cloning of A. vinelandii algC, encoding the enzyme catalyzing the second step of alginate pathway. We showed that AlgC is involved not only in alginate production, but also in lipopolysaccharide (LPS) synthesis and that it seems to have both phosphomannomutase and phosphoglucomutase activities. The transcriptional analysis of the A. vinelandii algC gene showed that it contained two start sites, one of which was dependent on the alternative sigma factor AlgU/AlgT. This finding explains why alginate biosynthesis is dependent on AlgU activity, since all other alginate biosynthetic genes have been characterized previously and algC is the only alginate structural gene that is directly transcribed by this sigma factor.

Asunto(s)

Azotobacter vinelandii/enzimología , Azotobacter vinelandii/genética , Genes Bacterianos , Ácido Glucurónico/biosíntesis , Lipopolisacáridos/biosíntesis , Fosfoglucomutasa/metabolismo , Fosfotransferasas (Fosfomutasas)/metabolismo , Alginatos , Proteínas Bacterianas/genética , Proteínas Bacterianas/aislamiento & purificación , Proteínas Bacterianas/metabolismo , Secuencia de Bases , Clonación Molecular , ADN Bacteriano/química , ADN Bacteriano/genética , ADN Bacteriano/aislamiento & purificación , Ácidos Hexurónicos , Datos de Secuencia Molecular , Fosfoglucomutasa/genética , Fosfoglucomutasa/aislamiento & purificación , Fosfotransferasas (Fosfomutasas)/genética , Fosfotransferasas (Fosfomutasas)/aislamiento & purificación , Proteínas Recombinantes/genética , Proteínas Recombinantes/aislamiento & purificación , Proteínas Recombinantes/metabolismo , Factores de Transcripción/metabolismo , Sitio de Iniciación de la Transcripción , Transcripción Genética