Biocontrol impact of AHL degrading actinobacteria on quorum sensing regulated virulence of phytopathogen Pectobacterium carotovorum subsp. carotovorum BR1

Abstract

The aim of this study was to isolate soilborne AHL degrading actinobacteria that can be used as biocontrol agents against the quorum sensing mediated virulence of Pectobacterium carotovorum subsp. carotovorum BR1 in in vitro and in planta studies. Actinobacterial strains capable of N-acyl homoserine lactone (AHL) degradation, Glutamicibacter nicotianae AI5a and Rhodococcus pyridinivorans AI4 were isolated and screened using Chromobacterium violaceum CV026 as a biosensor in an AHL degradation bioassay. The effect of AHL degradation by the potential biocontrol strains was studied by a co-culture assay. Reduction in plant cell wall degrading enzymes produced by PccBR1 due to the quorum quenching activity of the potential biocontrol strains was studied using colorimetric assays. The ability of the isolates to reduce soft rot symptoms was studied in in vitro cucumber and potato maceration assays. A cucumber plant infection model was developed to study blackleg in greenhouse experiments. G. nicotianae AI5a, R. pyridinivorans AI4 and R. erythropolis CRD13.3C were able to reduce 3-oxo-C6- N-acyl homoserine lactone and production of plant cell wall degrading enzymes by PccBR1. The isolates were also able to prevent and attenuate soft rot caused by PccBR1 in vitro in potato and cucumber maceration assays. The isolates were also able to prevent blackleg in an in planta cucumber infection model. Among the three actinobacterial isolates, G. nicotianae AI5a showed best results and has immense potential as a biocontrol agent against the virulence of the quorum sensing phytopathogen PccBR1.