Virulence factors
The Intracellular lifestyle of Salmonella
The intracellular lifestyle of Salmonella enterica and novel approaches to understand the adaptation to life within the Salmonella-containing vacuole
from Roopa Rajashekar and Michael Hensel writing in Salmonella: From Genome to Function
Salmonella enterica is a facultative intracellular pathogen that resides in a unique membrane-bound compartment, referred to as Salmonella-containing vacuole or SCV. Within the SCV, Salmonella is able to survive the antimicrobial activities of phagocytic cells and can rapidly multiply in a variety of host cells. Intracellular life of Salmonella is dependent on a large number of virulence traits, but the function of the type III secretion system (T3SS) encoded by Salmonella Pathogenicity Island 2 (SPI2) is of central importance. Although more than 20 effector proteins have been identified as translocated by the SPI2-T3SS, the molecular function and contribution to intracellular live is only known for a few of these proteins. Intracellular Salmonella modify basic functions of the host cell such as the structure of the microtubule cytoskeleton and induce a massive reorganization of vesicular transport and the endosomal system. Unique phenomena are the SPI2-dependent induction of extensive tubular membrane aggregations of endosomal or Golgi-derived vesicles. The SCV itself has features of a novel organelle and the fate of this compartment is controlled by the pathogen. Previous observations indicated that the SCV is arrested in the state of late endosomal compartment, but recent studies using advanced ultrastructural analyses and live cell studies indicate a complex and highly dynamic interaction of the intracellular Salmonella and their host cells.
Further reading: Salmonella: From Genome to Function
from Roopa Rajashekar and Michael Hensel writing in Salmonella: From Genome to Function
Salmonella enterica is a facultative intracellular pathogen that resides in a unique membrane-bound compartment, referred to as Salmonella-containing vacuole or SCV. Within the SCV, Salmonella is able to survive the antimicrobial activities of phagocytic cells and can rapidly multiply in a variety of host cells. Intracellular life of Salmonella is dependent on a large number of virulence traits, but the function of the type III secretion system (T3SS) encoded by Salmonella Pathogenicity Island 2 (SPI2) is of central importance. Although more than 20 effector proteins have been identified as translocated by the SPI2-T3SS, the molecular function and contribution to intracellular live is only known for a few of these proteins. Intracellular Salmonella modify basic functions of the host cell such as the structure of the microtubule cytoskeleton and induce a massive reorganization of vesicular transport and the endosomal system. Unique phenomena are the SPI2-dependent induction of extensive tubular membrane aggregations of endosomal or Golgi-derived vesicles. The SCV itself has features of a novel organelle and the fate of this compartment is controlled by the pathogen. Previous observations indicated that the SCV is arrested in the state of late endosomal compartment, but recent studies using advanced ultrastructural analyses and live cell studies indicate a complex and highly dynamic interaction of the intracellular Salmonella and their host cells.
Further reading: Salmonella: From Genome to Function
Salmonella virulence factors
Salmonella secreted virulence factors
from Fred Heffron, George Niemann, Hyunjin Yoon, Afshan Kidwai, Roslyn Brown, Jason McDermott, Richard Smith and Joshua Adkins writing in Salmonella: From Genome to Function
Research in the past twenty years has shown that Salmonella precisely manipulates their host by hierarchical secretion of virulence factors (effectors). More than 40 secreted virulence factors have been identified in Salmonella, but the function and mammalian targets of only a few are known. Effectors are directed to specific sub-cellular compartments and mammalian targets, and they mediate a diverse array of activities. Thus, the first half of this review focuses upon our understanding of effector mechanisms and their roles during infection.
However, the known effector repertoire is incomplete and the second half of this review places an emphasis on discovery. Computer analysis identified common secretion motifs and predicted that as many as 300 additional proteins may be secreted by Salmonella. In fact, mass spectrometry analysis identified a more complete secretome and found many novel, uncharacterized effector proteins. Several effectors identified in this study were small proteins of only 30-100 amino acids in length, suggesting that they are not enzymes but agonists or antagonists of specific host factors. One surprise from the mass spectrometry analysis was the identification of proteins that are secreted to mammalian cells via outer membrane vesicles. Complete characterization of the bewildering array of secreted proteins will take many years.
Further reading: Salmonella: From Genome to Function | Bacterial Secreted Proteins
from Fred Heffron, George Niemann, Hyunjin Yoon, Afshan Kidwai, Roslyn Brown, Jason McDermott, Richard Smith and Joshua Adkins writing in Salmonella: From Genome to Function
Research in the past twenty years has shown that Salmonella precisely manipulates their host by hierarchical secretion of virulence factors (effectors). More than 40 secreted virulence factors have been identified in Salmonella, but the function and mammalian targets of only a few are known. Effectors are directed to specific sub-cellular compartments and mammalian targets, and they mediate a diverse array of activities. Thus, the first half of this review focuses upon our understanding of effector mechanisms and their roles during infection.
However, the known effector repertoire is incomplete and the second half of this review places an emphasis on discovery. Computer analysis identified common secretion motifs and predicted that as many as 300 additional proteins may be secreted by Salmonella. In fact, mass spectrometry analysis identified a more complete secretome and found many novel, uncharacterized effector proteins. Several effectors identified in this study were small proteins of only 30-100 amino acids in length, suggesting that they are not enzymes but agonists or antagonists of specific host factors. One surprise from the mass spectrometry analysis was the identification of proteins that are secreted to mammalian cells via outer membrane vesicles. Complete characterization of the bewildering array of secreted proteins will take many years.
Further reading: Salmonella: From Genome to Function | Bacterial Secreted Proteins