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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Environmental Microbial & Food Safety Laboratory » Research » Publications at this Location » Publication #309711
Title: Swarm and swim motilities of Salmonella enterica serovar Typhimurium and role of osmoregulated periplasmic glucans

Author
item DHARNE, MAHESH - Council Of Scientific And Industrial Research (CSIR)
item KANNAN, PORTEEN - University Of Madras
item Murphy, Charles
item Smith, Allen
item Bhagwat, Arvind

Submitted to: Microbiology Discovery
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2015
Publication Date: 7/1/2015
Citation: Dharne, M., Kannan, P., Murphy, C.F., Smith, A.D., Bhagwat, A.A. 2015. Swarm and swim motilities of Salmonella enterica serovar Typhimurium and role of osmoregulated periplasmic glucans. Microbiology Discovery. 3:3.

Interpretive Summary: Controlling the spread of human pathogens on fresh produce is a top priority for public health reasons. Salmonella sp. migrate on wet surfaces by a movement called swarming motility. We investigated the role of periplasmic glucose polymer (glucans) in swarming motility. Using molecular and genetic techniques, mutations were generated in glucan synthesis genes. Out studies show that mutations in glucan synthesis genes inhibited flagella synthesis and as a result Salmonella cells were unable to exhibit mobility on wet surfaces; motility in liquid media remained unaffected. Understanding how pathogens migrate over wet surfaces will advance our knowledge of how enteric human pathogens enter our food chain. The research will benefit the fresh produce industry, as well as increasing the microbial food safety of the Americans food supply.

Technical Abstract: Background: Salmonella enterica serovar Typhimurium strains synthesize osmoregulated periplasmic glucans (OPGs) under low osmolarity conditions (< 70 mos mol l-1). OPG synthesis is not observed when cells are grown in iso- or hyper-osmotic media (> 400 mos mol l-1). Mutation in OPG structural genes namely, opgG and opgH, resulted in loss of OPG synthesis, reduced flagella synthesis and defective swimming motility in low osmotic media. OPGs are also needed to overcome cationic detergent stress and OPG mutants exhibit suboptimal mice virulence. Findings: Salmonella spp. Strains exhibit unique motility when placed on moist growth surfaces known as swarming motility. Here we report Salmonella sp. carrying mutation in opgGH genes are unable to exhibit swarm motility in spite of the fact that osmolarity of swarm medium exceeds 400 mos mol l-1. Plasmid carrying opgGH genes with site-directed mutations at the active site amino acid residues failed to restore swarm motility. Full length opgGH gene products were needed to support swarm motility even though no OPG synthesis was detected in media with osmolarity > 400 mos mol l-1. Conclusions: Since swarm motility promoting media are iso- or hyperosmotic (> 400 mos mol l-1), the requirement of opgGH genes for swarm motility appears to be indirect. Although OPG synthesis is expected to be repressed in media favoring swarm motility, transcription of opgGH was not repressed. Catalytically functional opgGH proteins are needed to support swarm motility.