Improved Methods for Treatment of Phytopathogenic Biofilms: Metallic Compounds as Anti-Bacterial Coatings and Fungicide Tank-Mix Partners.

Michael Harding,Greg Daniels,Amin Omar,Brenton Buziak,Patricia Nadworny,Jie Feng

doi:10.3390/molecules24122312

Abstract

Fungi and bacteria cause disease issues in cultivated plants world-wide. In most cases, the fungi and bacteria colonize plant tissues as biofilms, which can be very challenging to destroy or eradicate. In this experiment, we employed a novel (biofilm) approach to crop disease management by evaluating the efficacies of six fungicides, and four silver-based compounds, versus biofilms formed by fungi and bacteria, respectively. The aim was to identify combinations of fungicides and metallic cations that showed potential to improve the control of white mold (WM), caused by the ascomycete fungus Sclerotinia sclerotiorum, and to evaluate novel high valency silver compounds as seed coatings to prevent biofilm formation of four bacterial blight pathogens on dry bean seeds. Our results confirmed that mature fungal biofilms were recalcitrant to inactivation by fungicides. When metallic cations were added to the fungicides, their efficacies were improved. Some improvements were statistically significant, with one combination (fluazinam + Cu2+) showing a synergistic effect. Additionally, coatings with silver compounds could reduce bacterial blight biofilms on dry bean seeds and oxysilver nitrate was the most potent inhibitor of bacterial blight.

Highlights

Biofilms are multicellular communities of microorganisms attached to solid surfaces and encased in a self-produced polymeric matrix (EPS) [1]
Bacterial biofilms have been observed on the surfaces of dry bean seeds formed by the phytopathogenic bacteria Pseudomonas syringae pv. phaseolicola and Curtobacterium flaccumfaciens pv. flaccumfaciens
This study hypothesized that a biofilm approach to fungal and bacterial diseases on dry beans could lead to novel solutions, and that metallic cations may improve fungicide efficacies and provide effective coatings that prevent or reduce bacterial biofilm formation on seed

Summary

Introduction

Biofilms are multicellular communities of microorganisms attached to solid surfaces and encased in a self-produced polymeric matrix (EPS) [1]. Metal cations are frequently involved in, or essential for, vital physiological and metabolic cellular functions. Some metallic cations have been reported to enhance biofilm formation [3], while others have inhibitory or anti-biofilm properties [4]. One of the first interactions described for metal ions and biofilms was the binding of metals by the EPS [5]. The inhibition of biofilms by metal cations has been intensively studied revealing the powerful effects of these cations and their potential use in inhibition and remediation of biofilms [6,7,8,9]

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