Abstract

N-acylhomoserine lactone (AHL)-mediated Quorum sensing (QS) allows bacterial populations to communicate via the exchange of diffusible signals to coordinate gene expression and control adaptive behaviors in response to cell density in Gram-negative bacteria. Two luxIR-like QS systems splIR and spsIR have been characterized in an endophytic strain G3 of Serratia plymuthica. Here we reported a third LuxR homolog, SptR for better understanding the QS network by strain G3. Firstly, cloning and sequencing of asptR gene was performed using PCR; phylogenetic analysis revealed that SptR was not closely correlated to other members of LuxR-family protein in Serratia, but clustered into one clade with LuxR-family members from Enterobacter cloacae SCF1 and Erwinia tasmaniensis Et1/99 sharing a more common ancestor. Further mutational analysis of biocontrol-related phenotypes demonstrated that SptR served as a positive regulator to control production of exenzymes, as well as swimming motility and biofilm formation contrary to most LuxR homologs from Serratia as repressor. However, no significant impact on production of auxin indole-3-acetic acid (IAA) and antagonistic ability was observed. The results paved the way for further studies of the complex QS network and regulatory mechanisms involved in fine tuning of beneficial bacteria-plant interactions byS. plymuthica.

Key words: Serratia plymuthica, a LuxR-like SptR regulator, quorum sensing, exoenzymes, swimming motility, biofilm formation.