Many Gram-negative bacterial pathogens interact with mammalian cells by using type iii secretion systems (T3SS) to inject virulence proteins into host cells. A subset of these injected protein 'effectors' are enzymes that inhibit the function of host proteins by catalyzing the addition of unusual posttranslational modifications. The E. coli and Citrobacter rodentium NleB effectors, as well as the Salmonella enterica SseK 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 that keep the effectors in a structural state permissive for secretion. While performing mass spectrometry experiments to identify glycosylation substrates of nleB orthologs, we unexpectedly observed that the bacterial glutathione synthetase (GshB) is glycosylated by NleB on arginine residue R256. NleB-mediated glycosylation of GshB resulted in enhanced GshB activity, leading to an increase in glutathione production, and promoted C. rodentium survival in oxidative stress conditions. these data represent, to our knowledge, the first intra-bacterial activity for a T3SS effector and show that arginine-GlcnAcylation, once thought to be restricted to host cell compartments, also plays an important role in regulating bacterial physiology.
Taxa with geographically disjunct distributions and that are endemic or narrowly endemic face the real and immediate threat of local extinction because of inbreeding depression, genetic drift, and environmental stochasticity. These threats are amplified by the predicted changes in climate anticipated within the next 50 years, pointing to the increasing need for population genetic data and translocation experiments to track long-term evolutionary potential in rare plant species. In this study, we assessed population genetic structure within and among natural, augmented, and introduced populations of leafy prairie-clover (Dalea foliosa; Fabaceae) in a geographically disjunct region of the species range (i.e., Illinois) and predicted future potential changes in climate within the study region. Using six novel nuclear microsatellite loci to survey nine populations from Illinois and two from Tennessee, we found extremely limited genetic diversity and no structure among populations within Illinois, with greater genetic diversity within and between populations in Tennessee. Using future climate visualizations, we predict the Illinois portion of the species range will be warmer and wetter within the next 50 years, potentially increasing competition for D. foliosa habitat through woody encroachment. When considered together, these concerns point to the need to prioritize actions that will improve our understanding of the implications of translocations across geographically disjunct regions within the species range.
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