Osmoregulated periplasmic glucans of Salmonella enterica serovar Typhimurium are required for optimal virulence in mice

Abstract

We purified osmoregulated periplasmic glucans (OPGs) from Salmonella enterica serovar Typhimurium and found them to be composed of 100 % glucose with 2-linked glucose as the most abundant residue, with terminal glucose, 2,3-linked and 2,6-linked glucose also present in high quantities. The two structural genes for OPG biosynthesis, opgG and opgH, form a bicistronic operon, and insertion of a kanamycin resistance gene cassette into this operon resulted in a strain devoid of OPGs. The opgGH mutant strain was impaired in motility and growth under low osmolarity conditions. The opgGH mutation also resulted in a 2 log increase in the LD 50 in mice compared to the wild-type strain SL1344. Inability to synthesize OPGs had no significant impact on the organism's lipopolysaccharide pattern or its ability to survive antimicrobial peptides-, detergent-, pH-and nutrient-stress conditions. We observed that the opgGH-defective strain respired at a reduced rate under acidic growth conditions (pH 5.0) and had lower ATP levels compared to the wild-type strain. These data indicate that OPGs of S. Typhimurium contribute towards mouse virulence as well as growth and motility under low osmolarity growth conditions.

Determining RNA quality for NextGen sequencing: some exceptions to the gold standard rule of 23S to 16S rRNA ratio§

“…Salmonella enterica Serovar Typhimurium strain SL1344, Escherichia coli O157:H7 EDL933, Escherichia albertii USDA 181, and Citrobacter rodentium ATCC 51459 have been described earlier [2,3,8,11,16]. Bacterial cultures were streaked on Luria-Bertani (LB) agar plates from freezer stocks, and a single colony was inoculated in LB broth and grown at 37 o C in a shaker incubator for 18-20 h.…”

Swarm and swim motilities of Salmonella enterica serovar Typhimurium and role of osmoregulated periplasmic glucans

“…In S. enterica Serovar Typhimurium, mutations in opgGH operon result in compromised virulence [6,12]. Lack of OPG synthesis also show pleiotropic phenotypes such as extended lag time to enter a logarithmic growth phase as well as reduced swim-motility in low nutrient-low osmolarity media (with osmolarity <100 mMos Mol -1 ).…”

“…Studies in several microorganisms, including plant and animal pathogens as well as plant symbionts, have shown the importance of OPG in successful host invasion [6][7][8]. OPG synthesis-deficient mutants result in compromised virulence in plant-and animal-pathogenic microorganisms [6][7][8]. In symbiotic plant-microbe interactions, mutant cells fail to gain entry in plant roots [9,10].…”

“…In Escherichia coli, Salmonella enterica serovar Typhimurium and Shigella flexneri, OPG synthesis is catalyzed by the products of opgG and opgH genes, which are transcribed as a single operon [2,[4][5][6]. Studies in several microorganisms, including plant and animal pathogens as well as plant symbionts, have shown the importance of OPG in successful host invasion [6][7][8]. OPG synthesis-deficient mutants result in compromised virulence in plant-and animal-pathogenic microorganisms [6][7][8].…”

“…Large quantities of OPG are synthesized as the osmolarity of the surrounding medium decreases [3]. In Escherichia coli, Salmonella enterica serovar Typhimurium and Shigella flexneri, OPG synthesis is catalyzed by the products of opgG and opgH genes, which are transcribed as a single operon [2,[4][5][6]. Studies in several microorganisms, including plant and animal pathogens as well as plant symbionts, have shown the importance of OPG in successful host invasion [6][7][8].…”