First Demonstration of the Involvement of T4ss in Bacterial Killing
This immediately suggests the hypothesis that, since very few T4SS have been characterized to date, T4SS-mediated bacterial killing may not be restricted to the Xanthomonadaceae family, and may in fact be a more widespread phenomenon.
Citrus canker is a disease that has severe economic impact on the citrus industry worldwide. There are three types of canker, called A, B, and C. The three types have different phenotypes and affect different citrus species. The causative agent for type A is Xanthomonas citri subsp. citri, whose genome sequence was made available in 2002 . Bacterial cells are continuously interacting with other bacterial and eukaryotic cells in a battle for survival. These interactions have driven the evolution of several mechanisms by which they quickly deploy proteinaceous and nucleic acid effectors that manipulate the behaviour of the target organism, often resulting in growth inhibition or death. Distinct among these mechanisms are the type III, type IV and type VI secretion systems (T3SS, T4SS and T6SS, respectively) that are all capable of transferring proteins, and in the case of the T4SS, protein–DNA complexes, directly into neighbouring cells in a contact-dependent manner. All three of these systems have been shown to be able to inject virulence factors into eukaryotic hosts, but only the T6SSs have been shown to deliver lethal toxins into bacterial cells.