Bacterial persistence is characterized by the ability of a subpopulation within bacterial cultures to survive exposure to antibiotics and other lethal treatments. The surviving persisters are not the result of genetic changes but represent epigenetic variants that are in a physiological state where growth is inhibited. Since characterization of persisters has been performed mainly in Escherichia coli K-12, we sought to identify mechanisms of persistence in the pathogen Salmonella enterica serovar Typhimurium. Isolation of new highly persistent mutants revealed that the shpAB locus (Salmonella high persistence) imparted a 3-to 4-orderof-magnitude increase in survival after ampicillin exposure throughout its growth phase and protected the population against exposure to multiple antibiotics. Genetic characterization revealed that shpAB is a newly discovered toxin-antitoxin (TA) module. The high-persistence phenotype was attributed to a nonsense mutation in the 3= end of the shpB gene encoding an antitoxin protein. Characteristic of other TA modules, shpAB is autoregulated, and high persistence depends on the Lon protease.

During protein targeting by the signal recognition particle (SRP), signals from cargo binding in the SRP's M domain must be communicated to its GTPase domain to initiate the membrane delivery of cargo. In this study, a conserved fingerloop lining the signal sequence–binding groove of SRP is shown to provide a key link in this molecular communication.

Calcium oxalate crystal macropatterns in leaves were characterized for 69 species (and two Glycine tomentella cytotypes) from 14 of 16 genera in two legume groups, Glycine and Shuteria, to determine whether they share a common macropattern. A leaf clearing method was used to visualize the crystals. All 69 species (and two Glycine tomentella cytotypes) displayed prismatic crystals associated with leaf veins and vein endings. In contrast, mesophyll crystals occurred in 76.8% of 69 species and two G. tomentella cytotypes, and varied from a few to many. Conversely, only 40.9% of 22 Glycine species (in group Glycine) lacked mesophyll crystals, while 8.7% of 23 species of six genera associated with Glycine (in group Glycine) lacked mesophyll crystals. Thus 24.4% of 45 species of seven combined genera in group Glycine lacked mesophyll crystals. With seven genera in group Shuteria, 20.8% of 24 species lacked mesophyll crystals. The consistently present vein crystals varied in size and shape, so their length-width (Stubby versus Long) crystal ratios were determined for primary, secondary, and tertiary veins, and vein endings. Two trends were evident: Long-crystal ratios increased from primary veins to vein endings in species in both groups, and the perennial and annual Glycine species showed this condition to a greater extent than all the non-Glycine species. In some cases, taxonomically closely associated species were quite similar in their macropattern and presence or absence of mesophyll crystals. These results should be of value to future studies dealing with taxonomy and phylogeny of species in these two leguminous groups.Résumé : Afin de déterminer si ces espèces partagent un macropatron commun, les auteurs ont caractérisé les macropatrons des cristaux d'oxalate de calcium dans les feuilles de 69 espèces (et deux cytotypes du Glycine tomentella), appartenant à 14-16 genres des deux groupes Glycine et Shuteria, Ils ont utilisé une méthode d'éclaircissement pour visualiser les cristaux. L'ensemble des 69 espèces présente des cristaux prismatiques associés aux nervures et à leurs terminaisons. Au contraire, on n'observe les cristaux du mésophylle que chez 76,8 % des 69 espèces et les deux cytotypes du G. tomentella, et leur nombre varie de quelques-uns à plusieurs. Réciproquement, seulement 40,9 % des 22 espèces de Glycine (groupe Glycine) ne possèdent pas de cristaux dans leur mésophylle, alors que 8,7 % des 23 espèces de six genres associées au genre Glycine (groupe Glycine) ne possèdent pas de cristaux dans leur mésophylle. Ainsi 24,4 % des 45 espèces, appartenant à sept genres combinés du groupe Glycine, n'ont pas de cristaux dans leur mésophylle. Parmi les sept genres du groupe Shuteria, 20,8 % des 24 espèces sont dépourvues de cristaux du mésophylle. Les cristaux présents de façon constante dans les nervures varient en dimension et en forme, et les auteurs ont donc déterminé les rapports longueur-largeur (court contre allongé) des cristaux, pour les nervures de premier, deuxième et troisième ordres, ainsi que dan...