How bacteria hack each other’s mailing system

Oeiras, 02.10.2014

Bacteria coordinate behaviour through the production, release, and detection of chemical signals called autoinducers. While most autoinducers are species-specific, autoinducer-2 is used by many species and facilitates interspecies communication. Now a team of researchers from the ITQB, the IGC, the Champalimaud Centre for the Unknown and the Swarthmore College (US), has characterized the mechanism through which some bacteria are able to manipulate levels of autoinducer-2 in the environment, interfering with the communication of other species. The work is published in the Proceedings of the National Academy of Sciences of the United States of America.

Bacterial communication, or quorum sensing, works responding to bacterial concentration and triggering specific responses only when bacterial populations reach a determined threshold. Important bacterial behaviors, including virulence and biofilm formation, are regulated via this communication system. Researchers believe that methods for interfering with quorum sensing are promising alternatives to antibiotics.

The process through which bacteria, such as E. coli, are able to render useless the communication systems of their competitors involves the uptake of the quorum sensing autoinducer-2 (Al-2) via the Lsr transporter, followed by phosphorylation and consequent intracellular sequestration. Researchers have now completely determined the metabolic fate of intracellular AI-2 by characterizing, the terminal protein (LsrF) in the Lsr AI-2 processing pathway. According to the proposed catalytic model, based on crystal structures and NMR detected enzymatic reactions, LsrF catalyzes the transfer of an acetyl group from an isomer of AI-2-phosphate to coenzyme A yielding dihydroxyacetone phosphate and acetyl-CoA, two key central metabolites.

“Genome annotation and structural homologies can be extremely helpful in the elucidation of many biological processes but sometimes they can lead scientists in wrong directions”, says Karina Xavier, one the authors of the study. This was the case for LsrF enzyme, an enzyme previously annotated as an aldolase that actually catalyses a thiolytic cleavage by a completely novel reaction mechanism. “What we saw is another example of how Nature often learns how to use the same building blocks to perform novel functions”, the researcher concludes.

Original Article

PNAS (2014) 111 (39): 14235–14240 DOI: 10.1073/pnas.1408691111

LsrF, a coenzyme A-dependent thiolase, catalyzes the terminal step in processing the quorum sensing signal autoinducer-2

João C. Marques, Il Kyu Oh, Daniel C. Ly, Pedro Lamosa, M. Rita Ventura, Stephen T. Miller and Karina B. Xavier