טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentNatali Shirron
SubjectMolecular Study of the Interactions of Salmonella Entrica
and Plants
DepartmentDepartment of Biotechnology and Food Engineering
Supervisor Full Professor Yaron Sima


Abstract

The persistence of enteric pathogens in plants has been studied extensively during the past decade, mainly due to the potential hazard of enteric pathogens such as Salmonella enterica being able to invade and survive in/on plants. Following the thesis dissertation, we studied Salmonella’s interaction with plants using Nicotiana tabacum plants and cell culture and Salmonella Typhimurium as a model system. The research goal was to study the general characteristics of this interaction; more specifically, the ability of Salmonella to attach and penetrate the roots, transfer to other parts of the plant, survive, invade the plant cells, cause symptoms, and affect the plant physiology. We initially confirmed that Salmonella cells are able to affectively adhere to N .tabacum plants and cells. We continued with testing the ability of S. Typhimurium to transfer and persist in N. tabacum plants. Irrigating N. tabacum plants with Salmonella containing water resulted in an average bacterial count of 3.7 (±0.4) log CFU g-1 leaves. To understand how S. Typhimurium survives endophyticaly we conducted a detailed analysis on its ability to elicit or evade the plant immune response. Results indicate that Salmonella actively inhibits the production of an oxidative burst by the plant which meant to prevent the spread of an infection. This inhibition is contact dependent and most likely depends on Salmonella's factors; since a stronger response was observed by chloramphenicol treated Salmonella, by heat killed Salmonella or by purified LPS. By looking at the plant response to mutants defective in virulence factors we showed that the suppression depends on secreted factors indicating that a functional Type three secretion system is required for the suppression. To gain a broader picture of the mechanism, we also performed a mass spectrometry assay to detect changes in the secreted protein abundance, which are induced following infection of N. tabacum cells with Salmonella. Based on preliminary LC MS/MS analysis results we can concur that Salmonella induces several different pathways that are involved in various biological activities amongst which flagella and fimbria regulation and response to oxidative stress. This study demonstrates that plant colonization by S. Typhimurium is indeed an active process. S. Typhimurium utilizes adaptive strategies of altering innate plant perception systems to improve its fitness in the plant habitat.  All together by exploring the viability of S. Typhimurium in the plant habitat, we were able to support the hypothesis that plants are true hosts or vectors for Salmonella.