Azospirillum brasilense Az39, a model rhizobacterium with AHL quorum‐quenching capacity

GUALPA, J.; LOPEZ, G.; NIEVAS, S.; CONIGLIO, A.; HALLIDAY, N.; CÁMARA, M.; CASSÁN, F.

JOURNAL OF APPLIED MICROBIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2019 vol. 126 p. 1850 - 1860

1364-5072

AimsThe aim of this research was to analyse the quorum‐sensing (QS ) and quorum‐quenching (QQ ) mechanisms based on N ‐acyl‐l ‐homoserine lactones (AHL s) in Azospirillum brasilense Az39, a strain with remarkable capacity to benefit a wide range of crops under agronomic conditions.Methods and resultsWe performed an in silico and in vitro analysis of the quorum mechanisms in A. brasilense Az39. The results obtained in vitro using the reporter strains Chromobacterium violaceum and Agrobacterium tumefaciens and liquid chromatography coupled with mass‐mass spectrometry analysis showed that although Az39 does not produce AHL molecules, it is capable of degrading them by at least two hypothetical enzymes identified by bioinformatics approach, associated with the bacterial cell. In Az39 cultures supplemented with 500 nmol l−1 of the C3 unsubstituted AHL s (C4, C6, C8, C10, C12, C14), AHL levels were lower than in noninoculated LB media controls. Similar results were observed upon the addition of AHL s with hydroxy (OH ‐) and keto (oxo‐) substitutions in C3. These results not only demonstrate the ability of Az39 to degrade AHL s. They also show the wide spectrum of molecules that can be degraded by this bacterium.ConclusionsAlthough A. brasilense Az39 is a silent bacterium unable to produce AHL signals, it is able to interrupt the communications between other bacteria and/or plants by a QQ activity.Significance and Impact of the StudyThis is the first report confirming by unequivocal methodology the ability of A. brasilense , one of the most agriculturally used benefic bacteria around the world, to degrade AHL s by a QQ mechanism.