Mechanisms involved in resistance to bacteria Salmonella

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 when a 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."