Characterisation of two quorum sensing systems in the endophytic Serratia plymuthica strain G3: differential control of motility and biofilm formation according to life-style

Abstract

BackgroundN-acylhomoserine lactone (AHL)-based quorum sensing (QS) systems have been described in many plant-associated Gram-negative bacteria to control certain beneficial phenotypic traits, such as production of biocontrol factors and plant growth promotion. However, the role of AHL-mediated signalling in the endophytic strains of plant-associated Serratia is still poorly understood. An endophytic Serratia sp. G3 with biocontrol potential and high levels of AHL signal production was isolated from the stems of wheat and the role of QS in this isolate was determined.ResultsStrain G3 classified as Serratia plymuthica based on 16S rRNA was subjected to phylogenetic analysis. Using primers to conserved sequences of luxIR homologues from the Serratia genus, splIR and spsIR from the chromosome of strain G3 were cloned and sequenced. AHL profiles from strain G3 and Escherichia coli DH5α expressing splI or spsI from recombinant plasmids were identified by liquid chromatography-tandem mass spectrometry. This revealed that the most abundant AHL signals produced by SplI in E. coli were N-3-oxo-hexanoylhomoserine lactone (3-oxo-C6-HSL), N-3-oxo-heptanoylhomoserine lactone (3-oxo-C7-HSL), N-3-hydroxy-hexanoylhomoserine lactone (3-hydroxy-C6-HSL), N-hexanoylhomoserine lactone (C6-HSL), and N-heptanoyl homoserine lactone (C7-HSL); whereas SpsI was primarily responsible for the synthesis of N-butyrylhomoserine lactone (C4-HSL) and N-pentanoylhomoserine lactone (C5-HSL). Furthermore, a quorum quenching analysis by heterologous expression of the Bacillus A24 AiiA lactonase in strain G3 enabled the identification of the AHL-regulated biocontrol-related traits. Depletion of AHLs with this lactonase resulted in altered adhesion and biofilm formation using a microtiter plate assay and flow cells coupled with confocal laser scanning microscopy respectively. This was different from the closely related S. plymuthica strains HRO-C48 and RVH1, where biofilm formation for both strains is AHL-independent. In addition, QS in G3 positively regulated antifungal activity, production of exoenzymes, but negatively regulated production of indol-3-acetic acid (IAA), which is in agreement with previous reports in strain HRO-C48. However, in contrast to HRO-C48, swimming motility was not controlled by AHL-mediated QS.ConclusionsThis is the first report of the characterisation of two AHL-based quorum sensing systems in the same isolate of the genus Serratia. Our results show that the QS network is involved in the global regulation of biocontrol-related traits in the endophytic strain G3. However, although free-living and endophytic S. plymuthica share some conservation on QS phenotypic regulation, the control of motility and biofilm formation seems to be strain-specific and possible linked to the life-style of this organism.

Characterization of <i>N</i>-acyl homoserine lactones (AHLs) producing bacteria isolated from vacuum-packaged refrigerated turbot (<i>Scophthalmus maximus</i>) and possible influence of exogenous AHLs on bacterial phenotype

“…Morohoshi et al (2007) reported that an SpnR protein belonging to the LuxR family functioned as a negative regulator in Serratia marcescens. Liu et al (2011) have indicated that the production exoenzyme was positively regulated but indol-3-acetic acid was negatively regulated by QS in Serratia plymuthica G3 strain. Protease production regulated by C4-HSL and glucose in Aeromonas spp.…”

Serratia Infections: from Military Experiments to Current Practice

“…Two separate LuxIR-type systems, SplIR and SpsIR, have been identified in the plant pathogen S. plymuthica strain G3 (243). These two QS systems regulate antifungal activity, adhesion, biofilm production, and production of exoenzymes, but not swimming motility, in this strain (243).…”

“…QS, a cell-to-cell signaling mechanism employed by many bacteria, has been described for S. marcescens, S. plymuthica, and S. proteamaculans (243,392). Quorum sensing is used by bacteria to control certain biological functions, such as biofilm formation and the production of antibiotics (392).…”

Diversidade da microbiota endofítica na cultura da palma (Opuntia spp. e Nopalea spp.) no Semiárido de Pernambuco

“…A necessidade de estudos que visem a melhorar a resistência desta cultura contra ataques de insetos e microrganismos faz com que este estudo de diversidade de endofíticos tenha uma grande importância, principalmente porque estes estão envolvidos em muitas rotas metabólicas e podem ajudar na proteção da planta quanto a ataques de patógenos e pragas. Atualmente, tem sido demonstrado que a interação plantabactéria através do Quorum sensing (QS) é requerida para o sucesso da colonização das plantas pelas bactérias e que, em plantas associadas com bactérias Gram-negativas, uma molécula como AHLs (Acil Homoserina Lactona) é usada por micro-organismos simbióticos, patogênicos e estirpes de controle biológico para regular o amplo espectro de fenótipos, incluindo virulência, competência rizosférica, conjugação, secreção de enzimas hidrolíticas e produção de metabólitos secundários (LIU et al, 2011).…”