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

Won Jun^1,4,

Liu Liu^1,6,

Scott Angle^5,

¹ Produce Quality and Safety Laboratory, Henry A. Wallace Beltsville Agricultural Research Center, Agricultural Research Service, USDA, 10300 Baltimore Avenue, Bldg. 002, BARC-W, Beltsville, MD 20705-235, USA
² Diet Genomics and Immunology Laboratory, Henry A. Wallace Beltsville Agricultural Research Center, Agricultural Research Service, USDA, 10300 Baltimore Avenue, Bldg. 002, BARC-W, Beltsville, MD 20705-2350, USA
³ Food and Drug Administration, Division of Virulence Assessment, Laurel, MD 20708, USA
⁴ Department of Plant Science & Landscape Architecture, University of Maryland, College Park, MD 20742-7521, USA
⁵ College of Agriculture, University of Maryland, College Park, MD 20742-7521, USA
⁶ Department of Food Science and Nutrition, University of Maryland, College Park, MD 20742-7521, USA

Correspondence
Arvind A. Bhagwat
arvind.bhagwat{at}ars.usda.gov

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 LD₅₀ 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.

Present address: Food Safety Laboratory, USDA-ARS, Beltsville, MD 20705, USA.

Present address: College of Agricultural and Environmental Sciences, University of Georgia, Athens, GA 30602, USA.

Permanent address: North-west A&F University, Yangling, PR China.

||Permanent address: School of Life Sciences and Chemical Technology, Ngee Ann Polytechnic, Singapore 599489.

Supplementary methods (describing stress-tolerance experiments and phenotypic microarray analysis), figures and tables are available with the online version of this paper.