Type 3 secretion system

Type three secretion system (often written Type III secretion system and abbreviated TTSS or T3SS, also called Injectisome) is a protein appendage found in several Gram-negative bacteria.

In pathogenic bacteria, the needle-like structure is used as a sensory probe to detect the presence of eukaryotic organisms and secrete proteins that help the bacteria infect them. The secreted effector proteins are secreted directly from the bacterial cell into the eukaryotic (host) cell, where they exert a number of effects that help the pathogen to survive and to escape an immune response.

The term Type III secretion system was coined in 1993. This secretion system is distinguished from at least five other secretion systems found in Gram-negative bacteria. Many animal and plant associated bacteria possess similar T3SSs. These T3SSs are similar as a result of divergent evolution and phylogenetic analysis supports a model in which gram-negative bacteria can transfer the T3SS gene cassette horizontally to other species. The most researched T3SSs are from species of Shigella (causes bacillary dysentery), Salmonella (typhoid fever), Escherichia coli (Gut flora, some strains cause food poisoning), Vibrio (gastroenteritis and diarrhea), Burkholderia (glanders), Yersinia (plague), Chlamydia (sexually transmitted disease), Pseudomonas (infects humans, animals and plants) and the plant pathogens Erwinia, Ralstonia and Xanthomonas, and the plant symbiont Rhizobium.

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