Lysozyme enhances the bactericidal effect of BP100 peptide against Erwinia amylovora, the causal agent of fire blight of rosaceous plants

Jordi Cabrefiga,Emilio Montesinos

doi:10.1186/s12866-017-0957-y

Abstract

BackgroundFire blight is an important disease affecting rosaceous plants. The causal agent is the bacteria Erwinia amylovora which is poorly controlled with the use of conventional bactericides and biopesticides. Antimicrobial peptides (AMPs) have been proposed as a new compounds suitable for plant disease control. BP100, a synthetic linear undecapeptide (KKLFKKILKYL-NH2), has been reported to be effective against E. amylovora infections. Moreover, BP100 showed bacteriolytic activity, moderate susceptibility to protease degradation and low toxicity. However, the peptide concentration required for an effective control of infections in planta is too high due to some inactivation by tissue components. This is a limitation beause of the high cost of synthesis of this compound. We expected that the combination of BP100 with lysozyme may produce a synergistic effect, enhancing its activity and reducing the effective concentration needed for fire blight control.ResultsThe combination of a synhetic multifunctional undecapeptide (BP100) with lysozyme produces a synergistic effect. We showed a significant increase of the antimicrobial activity against E. amylovora that was associated to the increase of cell membrane damage and to the reduction of cell metabolism. Combination of BP100 with lysozyme reduced the time required to achieve cell death and the minimal inhibitory concentration (MIC), and increased the activity of BP100 in the presence of leaf extracts even when the peptide was applied at low doses. The results obtained in vitro were confirmed in leaf infection bioassays.ConclusionsThe combination of BP100 with lysozyme showed synergism on the bactericidal activity against E. amylovora and provide the basis for developing better formulations of antibacterial peptides for plant protection.

Highlights

Fire blight is an important disease affecting rosaceous plants
Cells treated with BP100 incorporated the SYTOX dye into the cytosol, but cell morphology and size were not modified compared to non-treated cells
Our results confirm that the bactericidal effect of BP100 against E. amylovora is mainly associated to the disruption of the bacterial cell membranes in agreement with some studies performed with BP100 in artificial membranes [36, 37, 50]

Summary

Introduction

Fire blight is an important disease affecting rosaceous plants. The causal agent is the bacteria Erwinia amylovora which is poorly controlled with the use of conventional bactericides and biopesticides. The peptide concentration required for an effective control of infections in planta is too high due to some inactivation by tissue components. This is a limitation beause of the high cost of synthesis of this compound. Most AMPs are small and cationic peptides with the capactiy to adopt an amphipathic conformation [12, 13] Their antimicrobial activity has been extensively related with the capacity to interact with the cell membranes [14]. This mode of action confers a broad spectrum of action, Cabrefiga and Montesinos BMC Microbiology (2017) 17:39 mainly against bacteria and fungi, and allows the penetration of peptide into the cell, favouring other mechanisms of action targeting nucleic acids and proteins [15,16,17,18,19,20]

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Conclusion