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United States Department of Agriculture

Agricultural Research Service

Research Project: GENETICS OF THE PATHOGEN-HOST-VECTOR INTERACTION IN SELECTED VEGETABLE CROPS

Location: Vegetable Crops Research Unit

Title: Environmental niche and temperature impact the role of Salmonella enterica diguanylate cyclases in plant colonization

Authors
item Cowles, Kimberly -
item Willis, David
item Barak, Jeri -

Submitted to: Molecular Genetics of Bacteria and Phage
Publication Type: Abstract Only
Publication Acceptance Date: June 7, 2013
Publication Date: August 6, 2013
Citation: Cowles, K.N., Willis, D.K., Barak, J.D. 2013. Environmental niche and temperature impact the role of Salmonella enterica diguanylate cyclases in plant colonization [abstract]. Molecular Genetics of Bacteria and Phage.

Technical Abstract: Although enteric human pathogens are usually studied in the context of their animal hosts, it has become increasingly apparent that a significant portion of their life cycle occurs on plants. Their adaptation to this environment has led to increased incidence of human disease, particularly in the context of fresh produce. Salmonella enterica is commonly introduced to plants through contaminated water used for irrigation or pesticide application. Thus, we predict that the ability to transition from a motile lifestyle (in water) to a more sessile lifestyle (on plants) would impact bacterial success. The transition to one well-studied sessile lifestyle, biofilm formation, is governed by the signaling molecule cyclic dimeric GMP (c-di-GMP). As with many other bacteria, S. enterica has multiple proteins that affect c-di-GMP production. Diguanylate cyclases (GGDEF-containing proteins) synthesize c-di-GMP while phosphodiesterases (proteins containing EAL or HD/GYP domains) degrade c-di-GMP. S. enterica has 5 GGDEF proteins, 8 EAL proteins, and 7 proteins containing both GGDEF and EAL domains. The presence of multiple proteins involved in the production of a single molecule suggests potential redundancy of function or environmental regulation of activity. We hypothesize that a subset of Gcps are active in a particular environment. To address this question, we have examined the role of each gcp in two plant environments: roots (where S. enterica encounters abundant nutrients and grows exponentially) and leaves (a relative ‘desert’ compared to roots where S. enterica persists with no net growth). To date, we have found that 3 Gcps (gcpA, gcpC, and yhdA) are needed for root colonization in a temperature dependent manner and 2 Gcps (adrA and yhdA) are important for persistence on leaves. Preliminary results suggest that none of the proteins with only EAL domains are required for root colonization but their role in phyllosphere colonization has not yet been tested. We also monitored transcript levels of the 20 genes involved in c-di-GMP production during root colonization and found that only adrA is differentially expressed. Currently, we are investigating the connection between adrA expression and the potential redundancy amongst S. enterica Gcps. By examining the Gcp regulational hierarchy, we hope to provide insight into the mechanisms that S. enterica uses to persist on plants as well as add to the growing knowledge regarding c-di-GMP production and regulation.

Last Modified: 7/30/2014
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