Public Release:  Mechanisms involved in resistance to the bacteria Salmonella studied in a Ph.D. thesis

Violeta Zorraquina, awarded a Ph.D. by the UPNA/NUP-Public University of Navarre, seeks to design strategies for preventing the incidence of Salmonella in factories and on farms

Elhuyar Fundazioa

This press release is available in Spanish.

In their natural environment bacteria develop by forming communities of micro-organisms called biofilms that afford them greater resistance. These biofilms on farms and premises where food is processed lead to considerable economic losses besides being a potential source of contamination and transmission of the pathogen. In her PhD thesis,Violeta Zorraquino-Salvo has studied a specific protein type that activates the formation of biofilm in Salmonella and regulates bacterial motility. "Having a better idea of the mechanisms involved in these processes will help to design new, more effective strategies for preventing the formation of biofilm and its potential harm in the clinical, food and industrial ambit," points out the researcher.

Two decades ago it was discovered that a small molecule (the so-called c-di-GMP) could on its own hamper motility and activate the formation of biofilm. "This molecule is part of a signal transduction system: there are different sensory membranes on the membrane of the bacteria that pick up stimuli from the outside and transduce them into different intracellular levels of c-di-GMP, thus regulating different biological processes like biofilm formation. "In the first part of her thesis Zorraquino removed all the sensory proteins from the Salmonella's genome."We created a mutant Salmonella incapable of picking up stimuli from the medium in which it lives and therefore of producing biofilm under any circumstances. "After that, each sensory protein was inserted one by one to be able to analyse, under different ambient conditions, how each one contributed to the formation of biofilm. "We showed that under each condition tested, only some proteins are active, so each one is most likely responsible for the formation of biofilm whena given condition is present."

These results have enabled researchers to get a better idea about the mechanism by which Salmonella activates the formation of biofilm. "We have generated new knowledge that could be used to design new strategies to help to prevent the formation of biofilm in our factories and on our farms," as Violeta Zorraquino pointed out.

Bacterial motility

The second part of her research focussed on studying the effect of the same molecule (c-di-GMP) in another of Salmonella's biological processes: bacterial motility.A bacterium is capable of moving freely in a liquid medium by rotating its flagella, and when it reaches a suitable surface, it sticks to it and begins to create the biofilm."There is an intervening step--between being motile and sticking to a surface--in which the bacterium has to stop the rotation of its flagella completely. We have discovered what is responsible for this intervening step: cellulose, which is a component of biofilm, and the synthesis of which is activated in the presence of the c-di-GMP molecule."

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Violeta Zorraquino graduated in Agricultural Engineering at the UPNA/NUP and obtained a Master's in Biotechnology at the Wageningen Universiteit (the Netherlands). Her PhD thesis "Análisis de la vía de transducción de señalmediadapor c-di-GMP en Salmonella: mecanismos de especificidad y regulación de la movilidad" [Analysis of the signal transduction route in which c-di-GMP intervenes in Salmonella: specificity mechanisms and motility regulation] was supervised by the PhD holders Cristina Solano-Goñi and Iñigo Lasa-Uzcudun, of the Department of Agrarian Production of the Public University of Navarre, and was awarded a pass with distinction.

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