Cell-Contact-Stimulated Formation of Filamentous Appendages by Salmonella typhimurium Does Not Depend on the Type III Secretion System Encoded by Salmonella Pathogenicity Island 1

Abstract

The formation of filamentous appendages on Salmonella typhimurium has been implicated in the triggering of bacterial entry into host cells (C. C. Ginocchio, S. B. Olmsted, C. L. Wells, and J. E. Galán, Cell 76:717–724, 1994). We have examined the roles of cell contact and Salmonellapathogenicity island 1 (SPI1) in appendage formation by comparing the surface morphologies of a panel of S. typhimurium strains adherent to tissue culture inserts, to cultured epithelial cell lines, and to murine intestine. Scanning electron microscopy revealed short filamentous appendages 30 to 50 nm in diameter and up to 300 nm in length on many wild-type S. typhimurium bacteria adhering to both cultured epithelial cells and to murine Peyer’s patch follicle-associated epithelia. Wild-type S. typhimuriumadhering to cell-free culture inserts lacked these filamentous appendages but sometimes exhibited very short appendages which might represent a rudimentary form of the cell contact-stimulated filamentous appendages. Invasion-deficient S. typhimurium strains carrying mutations in components of SPI1 (invA,invG, sspC, and prgH) exhibited filamentous appendages similar to those on wild-type S. typhimurium when adhering to epithelial cells, demonstrating that formation of these appendages is not itself sufficient to trigger bacterial invasion. When adhering to cell-free culture inserts, anS. typhimurium invG mutant differed from its parent strain in that it lacked even the shorter surface appendages, suggesting that SPI1 may be involved in appendage formation in the absence of epithelia. Our data on S. typhimurium strains in the presence of cells provide compelling evidence that SPI1 is not an absolute requirement for the formation of the described filamentous appendages. However, appendage formation is controlled by PhoP/PhoQ since a PhoP-constitutive mutant very rarely possessed such appendages when adhering to any of the cell types examined.

Membrane tubules attach Salmonella Typhimurium to eukaryotic cells and bacteria

“…Initial studies with tubular appendages of S. Typhimurium (60 nm in diameter) and epithelial MDCK cells or murine Peyer's patch follicle-associated epithelia (Ginocchio et al, 1994;Reed et al, 1998) described these as specific eukaryotic cell-induced structures (Ginocchio et al, 1994;Reed et al, 1998). In our experiments, tubular appendages of the same diameter connected bacteria to substrata or to bacteria in biofilms in the absence of eukaryotic cells.…”

“…R-type straight flagella of Salmonella are 5-11 nm (Mimori et al, 1995) and pili do not exceed 6-7 nm (Merz et al, 2000;Zhang et al, 2000), whereas aggregative fimbriae or curli are far smaller. High-resolution scanning electron microscopy studies revealed that contact with cultured epithelial cells results in the formation of unusually wide (60 nm in diameter) tubular appendages of S. Typhimurium attaching bacteria to the epithelial cells (Ginocchio et al, 1994;Reed et al, 1998). The formation of such appendages did not require de novo protein synthesis and was transient.…”

Genes encoding putative effector proteins of the type III secretion system of Salmonella pathogenicity island 2 are required for bacterial virulence and proliferation in macrophages

“…EspA is a component of a filamentous surface appendage that forms a contact between the bacterium and the eukaryotic cell surface (Knutton et al ., 1998). These structures resemble specific appendages (invasomes) that can be detected on the surface of S. typhimurium during epithelial cell invasion, although their relationship to the SPI‐1 type III secretion system is uncertain (Ginocchio et al ., 1994; Reed et al ., 1998). The SPI‐1 secretion system forms a needle‐like structure that spans the bacterial cell envelope (Kubori et al ., 1998).…”

Cytonemes Versus Neutrophil Extracellular Traps in the Fight of Neutrophils with Microbes

“…These membrane sheaths were often beaded to a variable degree and often did not contain flagella filaments [114]. Outer membrane tubular appendages interconnect bacteria Salmonella typhimurium in biofilms and attach bacteria to eukaryotic cells and substrates [18,115,116]. The diameter of the appendages (60 nm) significantly exceeded the diameter of the bacterial flagella (15-20 nm) or pili (6-7 nm).…”