Gram-negative bacterial pathogens interact with the host cells by using type III secretion systems (T3SS) to inject virulence proteins into cells. NleB effectors are glycosyltransferases that modify host protein substrates with N-acetyl glucosamine (GlcNAc) on arginine residues. This post-translational modification disrupts the normal functioning of host immune response proteins. T3SS effectors are thought to be inactive within the bacterium and fold into their active conformations after they are injected, due to the activity of chaperones . El Qaidi, et al (2020) reported that the bacterial glutathione synthetase (GshB) is glycosylated by NleB resulted in enhanced GshB activity, leading to an increase in glutathione production, and promoted bacterial survival in oxidative stress conditions. Is it possible that true role of T3SS effectors in bacteria was overlooked?
El Qaidi, S., Scott, N.E., Hays, M.P. et al. An intra-bacterial activity for a T3SS effector. Sci Rep 10, 1073 (2020). https://doi.org/10.1038/s41598-020-58062-y
(4) (PDF) An intra-bacterial activity for a T3SS effector (researchgate.net)
There are many examples of proteins and pathways that serve multiple roles. So it is certainly possible that the T3SS has multiple roles which include both stress response and virulence and these activities may be regulated differently as well. There is no real answer to which is the "true" role.
Michael J. Benedik Pathogenic bacteria is a well-studied genetically narrow part of bacterial world. They are overrepresented in genetic research because of their important hosts. In these bacteria T3SS looks rather conservative, but the postulated evolution of T3SS from flagellar system (Abby, Sophie S., and Eduardo PC Rocha. "The non-flagellar type III secretion system evolved from the bacterial flagellum and diversified into host-cell adapted systems." (2012): e1002983; and Diepold A, Armitage JP. Type III secretion systems: the bacterial flagellum and the injectisome. Philosophical Transactions of the Royal Society B: Biological Sciences. 2015 Oct 5;370(1679):20150020.) still has some gaps. Early forms of T3SS must give some benefits to the bacteria even in absence of host eukaryotic organism.
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