P-031. Osmoregulated Periplasmic Glucans (OPGs) of Salmonella enterica serovar Typhimurium Are Needed for Optimal Growth under Nutrient Limiting- Hypoosmotic Conditions

L. Liu1,2, P. Kannan2, J. Meng3, A. A. Bhagwat2;
1Northwest A&F Univ., Yangling, CHINA, 2USDA-ARS, Beltsville, MD, 3Univ. of Maryland, College Park, MD.

Background: Osmoregulated periplasmic glucans (OPGs) are major periplasmic constituents of gram negative bacteria. Synthesis of OPGs is regulated by the osmolarity of the growth medium. The role of OPGs has been postulated in plant-symbiotic as well as pathogenic microorganisms. On the other hand, opg mutants of E. coli carried no obvious phenotypes. Methods: We examined the growth of wild-type and opgGH mutants of Salmonella enterica serovar Typhimurium under nutrient limiting and hypoosmotic conditions (i.e., dilute LB media). We used vegetable wash waters obtained from various leafy green vegetables and examined the growth and biofilm formation (crystal violet staining of microtitre plates) in pure as well as in mixed culture settings. Results: We observed that wash waters obtained from spinach, celery, cilantro, green collard, broccoli, green cabbage, parsley and lettuce supported growth of Salmonella spp.. On the other hand, poor growth was observed in wash waters obtained from carrot and green onion. The ability to synthesize wild-type OPGs was of significant advantage for cells and the opgGH mutant grew at a significantly slower rate in vegetable wash waters. Low or slow growth of opgGH mutants did not affect biofilm formation. In mixed culture settings the slower growth rate of the opgGH mutant was detrimental and the mutant was out numbered by wild-type cells by 5 to 10-fold. Conclusion: The inability to synthesize wild-type OPGs affected the organism’s growth under nutrient limiting conditions. It also influenced competitive growth in mixed culture settings.