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Salmonella is one of the most common cause of the food borne illness. Salmonella belongs to Enterobacteriacae family and consists of 2 species, which diverge on 6 subspecies.These subspecies consists of 2700 serovars. There are typhoid serovars among them - S. Typhi, Paratyphi A, B, C - which cause typhoid fever in human. The rest of the serovars are non-typhoidal and leads to gastroenteritis both in animal and human. Salmonella enters to a mammal organism as a result of consumption of contaminated food products: meat, eggs, milk and products containing them. The entry of the infection for salmonellosis is the small intestine mucosa. Salmonella attaches to cell walls by fimbria and pili. Salmonella has several systems that are activated in response to adverse conditions such as: high osmolarity, acid or heat shock and nutrient deficiencies. They are based on the principle of a two-component system in which there is a sensor that receives cytoplasmic signals, and a regulator. Regulator (usually DNA-binding protein) initiates the transcription of the virulence genes (Chakraborty, 2015). The sensor is histidine kinase, which phosphorylates the regulatory protein, thereby activating it.During the infectious cycle of salmonella in mammalian organism the formation of specific vacuole SCV takes place (Salmonella-containing vacuole-containing vacuole containing salmonella) in the cytoplasm of the eukaryotic cell (Steele-Mortimer, 2008). SCV is a modified phagosome, which is formed as a result of cytoskeleton rearrangements. The target are usually phagocytic cells : neutrophils, macrophages and epithelial cells of the small intestine mucosa - M-cells (Akhmetova, 2012). Given the specific mechanism of infection, salmonella is considered a facultative intracellular pathogen. Bacterium invades the eukaryotic cell by rearrangement of its cytoskeleton with effector proteins and continue to persistence in a form of SCV. It is well-known nowadays that tolerance to high osmotic pressure is achieved through the EnvZ / OmpR system, which also regulates the expression of the ssrAB operon that is localized on the Salmonella pathogenicity island SPI-2 and triggers the expression of the effector proteins. The ssrAB operon is also regulated by the two-component acid shock response system PhoP / PhoQ (Worley, 2000). The functioning of the PhoP / PhoQ system directly depends on the sigma factor RpoS, which accumulates under low concentrations of magnesium cations (Tu, 2006). According to the researches of transduction between the EnvZ / OmpR components, it is clear that salmonella receives signals from the cytoplasmic environment, and sensory molecules are located on the inner membrane (Kenney, 2019; Wang et al., 2012). The ability to survive under acid shock is provided by the PhoP / PhoQ system, which also operates on the principle of signal transduction. PhoQ is a Histidine Kinase Signal Sensor. Signals are acidic pH, divalent cations and positively charged antimicrobial peptides. An important function of the two-component PhoP / PhoQ system is the control of spi ssa gene expression in a macrophage environment (Bijlsma, 2005). These genes are the main component of the type III secretion systems and are transcribed only when salmonella enters eukaryotic cell. (Bijlsma, 2005). The main regulator of signal transduction systems PhoP/PhoQ and EnvZ/OmpR is sigma-factor RpoS - subunit of bacterial RNA-polymerase - which operates in stationary phase at low pH, high omolarity, heat shock or nutrient deficiency. RpoS protein accumulates in adverse conditions during stationary phase (Mg2+ deficiency, low pH, high osmolarity). Need in magnesium cations is dependent on their ability to act as cofactors in many enzymatic activities. The accumulation begins at exponential (logarithmic) phase of bacterial reproduction. This is the phase of active cell division. Two factors MgtA and MgtB are responsible for Mg2+ transport. Another molecule with the same function is CorA - bivalent cation channel, though its transcriptions doesn’t depent on magnesium concentration in cell. In a case of magnesium deficiency at the stationary phase, RpoS accumulates vigorously an initiates replication of PhoP/PhoQ. PhoP/PhoQ regulates tolerance to inorganic acids. Also, PhoP/PhoQ controls adaptation to magnesium cations deficiency and macrophage activity. Results of many studies on genes coding this system and their mutations led to conclusion the mutation or inactivation of one factor causes decrease in virulence and makes bacterial susceptible to acid environment. To date, the stages of the infectious process for salmonellosis have been studied and described in detail in the literature. Particular attention is paid to signal transduction systems that are common among enterobacteria and help to avoid adverse conditions. Their functioning and regulation are investigated. It is known that salmonella receives signals for the activation of sensors from the cytoplasm, but the nature of these signals is not yet fully understood. Adaptation of the bacteria to adverse conditions and the response to phagocytosis is initiated by the transcription of pathogenic genes and the suppression of the transcription of the operon, which neutralize the conditions in the cytoplasm of salmonella cells. Thus, adapting to the conditions of target cells, salmonella continues to multiply in the body. Key words: salmonella, pH, osmolarity, virulencegenes, operon, signal transduction.
Salmonella is one of the most common cause of the food borne illness. Salmonella belongs to Enterobacteriacae family and consists of 2 species, which diverge on 6 subspecies.These subspecies consists of 2700 serovars. There are typhoid serovars among them - S. Typhi, Paratyphi A, B, C - which cause typhoid fever in human. The rest of the serovars are non-typhoidal and leads to gastroenteritis both in animal and human. Salmonella enters to a mammal organism as a result of consumption of contaminated food products: meat, eggs, milk and products containing them. The entry of the infection for salmonellosis is the small intestine mucosa. Salmonella attaches to cell walls by fimbria and pili. Salmonella has several systems that are activated in response to adverse conditions such as: high osmolarity, acid or heat shock and nutrient deficiencies. They are based on the principle of a two-component system in which there is a sensor that receives cytoplasmic signals, and a regulator. Regulator (usually DNA-binding protein) initiates the transcription of the virulence genes (Chakraborty, 2015). The sensor is histidine kinase, which phosphorylates the regulatory protein, thereby activating it.During the infectious cycle of salmonella in mammalian organism the formation of specific vacuole SCV takes place (Salmonella-containing vacuole-containing vacuole containing salmonella) in the cytoplasm of the eukaryotic cell (Steele-Mortimer, 2008). SCV is a modified phagosome, which is formed as a result of cytoskeleton rearrangements. The target are usually phagocytic cells : neutrophils, macrophages and epithelial cells of the small intestine mucosa - M-cells (Akhmetova, 2012). Given the specific mechanism of infection, salmonella is considered a facultative intracellular pathogen. Bacterium invades the eukaryotic cell by rearrangement of its cytoskeleton with effector proteins and continue to persistence in a form of SCV. It is well-known nowadays that tolerance to high osmotic pressure is achieved through the EnvZ / OmpR system, which also regulates the expression of the ssrAB operon that is localized on the Salmonella pathogenicity island SPI-2 and triggers the expression of the effector proteins. The ssrAB operon is also regulated by the two-component acid shock response system PhoP / PhoQ (Worley, 2000). The functioning of the PhoP / PhoQ system directly depends on the sigma factor RpoS, which accumulates under low concentrations of magnesium cations (Tu, 2006). According to the researches of transduction between the EnvZ / OmpR components, it is clear that salmonella receives signals from the cytoplasmic environment, and sensory molecules are located on the inner membrane (Kenney, 2019; Wang et al., 2012). The ability to survive under acid shock is provided by the PhoP / PhoQ system, which also operates on the principle of signal transduction. PhoQ is a Histidine Kinase Signal Sensor. Signals are acidic pH, divalent cations and positively charged antimicrobial peptides. An important function of the two-component PhoP / PhoQ system is the control of spi ssa gene expression in a macrophage environment (Bijlsma, 2005). These genes are the main component of the type III secretion systems and are transcribed only when salmonella enters eukaryotic cell. (Bijlsma, 2005). The main regulator of signal transduction systems PhoP/PhoQ and EnvZ/OmpR is sigma-factor RpoS - subunit of bacterial RNA-polymerase - which operates in stationary phase at low pH, high omolarity, heat shock or nutrient deficiency. RpoS protein accumulates in adverse conditions during stationary phase (Mg2+ deficiency, low pH, high osmolarity). Need in magnesium cations is dependent on their ability to act as cofactors in many enzymatic activities. The accumulation begins at exponential (logarithmic) phase of bacterial reproduction. This is the phase of active cell division. Two factors MgtA and MgtB are responsible for Mg2+ transport. Another molecule with the same function is CorA - bivalent cation channel, though its transcriptions doesn’t depent on magnesium concentration in cell. In a case of magnesium deficiency at the stationary phase, RpoS accumulates vigorously an initiates replication of PhoP/PhoQ. PhoP/PhoQ regulates tolerance to inorganic acids. Also, PhoP/PhoQ controls adaptation to magnesium cations deficiency and macrophage activity. Results of many studies on genes coding this system and their mutations led to conclusion the mutation or inactivation of one factor causes decrease in virulence and makes bacterial susceptible to acid environment. To date, the stages of the infectious process for salmonellosis have been studied and described in detail in the literature. Particular attention is paid to signal transduction systems that are common among enterobacteria and help to avoid adverse conditions. Their functioning and regulation are investigated. It is known that salmonella receives signals for the activation of sensors from the cytoplasm, but the nature of these signals is not yet fully understood. Adaptation of the bacteria to adverse conditions and the response to phagocytosis is initiated by the transcription of pathogenic genes and the suppression of the transcription of the operon, which neutralize the conditions in the cytoplasm of salmonella cells. Thus, adapting to the conditions of target cells, salmonella continues to multiply in the body. Key words: salmonella, pH, osmolarity, virulencegenes, operon, signal transduction.
Translation elongation is a multi-step process orchestrated by elongation factors.Elongation factors G and Tu are required for each round of translation elongation, whereas elongation factor P is only required to assist the translation of poly(Pro) sequences. Upon incorporation of consecutive proline residues the ribosome is stalled; this stalling is alleviated by EF-P. While the catalytic mechanism of EF-P is well described, the determinants of EF-P binding remain unknown. Structural data and biochemical studies suggest the E-site codon, the peptidyl-tRNA, the ribosomal protein L1 and the post-translational modification of EF-P as key interaction partners during binding and EF-P assisted catalysis.In this thesis we developed a FRET based EF-P binding assay using fluorescence-labeled ribosome complexes and a quencher-labeled EF-P. We combined the binding assay with different EF-P activity assays to determine the contribution of each of the proposed interactions to the binding and the catalytic activity of EF-P. We found that EF-P binds to different ribosome complexes with similar rates. EF-P has a short residence time on complexes without poly(Pro) stalling sequences, which is significantly increased on poly(Pro)-stalled complexes. This high affinity state depends on the presence of several recognition elements in poly(Pro)-stalled complexes, in particular tRNA Pro in the P site and the polypeptide chain containing several sequential proline residues. The contextindependent association rates and the determined cellular concentration of EF-P suggest that the sampling of ribosome complexes by EF-P is kinetically controlled by the availability of a vacant E site. However, only poly(Pro)-stalled ribosome complexes provide the interactions required for the high-affinity binding of EF-P. The dissociation rates from Pro-stalled and non-stalled complexes match the reported rates of EF-P-assisted peptide bond formation. This suggests a mechanism in which the prolonged residence time for stalled complexes allows EF-P to position the peptidyl-tRNA in a catalytically active conformation and thereby to alleviate the stalling. After peptide bond formation the complex returns to the low affinity state, inducing dissociation of EF-P. The proposed kinetic regime allows EF-P to efficiently sample ribosomes with empty E sites, to recognize Pro-stalled complexes with high turnover rates and to alleviate stalling in a single functional cycle. Thus, our work demonstrates that the recruitment of EF-P is kinetically controlled contributing to a harmonized rate of translation. when fMet-tRNA fMet recognizes the AUG start codon displayed by the mRNA (Milon et al., 2008). Joining of the 50S subunit triggers the GTPase activity of IF2, causing GTP hydrolysis and resulting in the dissociation of IF1 and IF2. The dissociation of IF3 marks the formation of the translation competent 70S IC (Goyal et al., 2015;Grigoriadou et al., 2007;Tomsic et al., 2000). The translation competent 70S IC provides three binding sites for tRNAs, the acceptor site...
Nutritional immunity is a powerful strategy at the core of the battlefield between host survival and pathogen proliferation. A host can prevent pathogens from accessing biological metals such as Mg, Fe, Zn, Mn, Cu, Co or Ni, or actively intoxicate them with metal overload. While the importance of metal homeostasis for the enteric pathogen Salmonella enterica Typhimurium was demonstrated many decades ago, inconsistent results across various mouse models, diverse Salmonella genotypes, and differing infection routes challenge aspects of our understanding of this phenomenon. With expanding access to CRISPR-Cas9 for host genome manipulation, it is now pertinent to re-visit past results in the context of specific mouse models, identify gaps and incongruities in current knowledge landscape of Salmonella homeostasis, and recommend a straight path forward towards a more universal understanding of this historic host-microbe relationship.
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