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The isolation and characterisation of marine bacteria with quorum-quenching activity for the treatment of infectious bacterial diseases

16th national competition for scientific and technical research

Marine sciences

Senior Researcher : Ana María Otero Casal

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Research Centre or Institution : Universidad de Santiago de Compostela.


Many pathogenic bacteria coordinate the expression of their virulence factors by means of an intercellular communication system known as Quorum Sensing (QS). For this purpose they produce small signal molecules which they secrete into the environment. As important bacterial pathogens lose much of their virulence when their QS systems are deactivated, there is enormous interest in the development of strategies to intercept QS signals to treat and prevent bacterial infections, a mechanism that has been called generically Quorum Quenching (QQ). Recent studies by the group have demonstrated the enormous potential of the marine environment for the isolation of bacterial strains with QQ activity, obtaining isolated bacteria with enzymatic QQ activity more than 2 orders of magnitude greater than those isolated in other habitats. This project aims to characterise the strains isolated with QQ activity beforehand, exploring QQ activity more fully in this medium, to obtain new isolated bacteria with QQ activity. During 2012, efforts have centred on cloning and characterising the QQ enzymes of marine bacteria 20J. A new lactonase has been cloned, denominated Aii20J, which has conserved the zinc binding domains typical of these enzymes, but with low homology with the lactonase of Bacillus thuringiensis (I.D.=30%). The gene was sub-cloned in the inducible vector pET28c+ for its over-expression in E.coli BL21DE3, which made it possible to purify and characterise the enzyme. The kinetics, specificity, temperature resistance, pH and proteases of the purified enzyme were characterised, with the aim of creating the basis for its industrial application. In the second year, the task of isolating and characterising marine bacteria with new QQ activities will commence.

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