Induction of a viable but not culturable (VBNC) state in some Pseudomonas syringae pathovars upon exposure to oxidation of an apoplastic phenolic, acetosyringone

Authors: Baker, Con; Mock, Norton; AVERYANOV, ANDREY - Russian Institute Of Phytopathology

Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2014
Publication Date: 1/1/2015
Citation: Baker, C.J., Mock, N.M., Averyanov, A.A. 2015. Induction of a viable but not culturable (VBNC) state in some Pseudomonas syringae pathovars upon exposure to oxidation of an apoplastic phenolic, acetosyringone. Physiological and Molecular Plant Pathology. 89:16-2.

Interpretive Summary: Bacterial plant diseases cause major damage to crops each year and the cost of controlling them adds greatly to production costs and often involves antibiotics which are a public concern. The plant leaf is the first line of defense against most of these pathogens. Increased knowledge of the molecular interactions that occur when bacteria invade the leaf can improve resistance and increase yield. In this manuscript we are reporting a previously unknown mechanism that plant cells may currently be using against bacteria. It involves the oxidation of metabolites that are found in the leaf and their ability to stop bacterial growth. This may present a new strategy for disease control that could be incorporated in plants, increasing these metabolites either through traditional or molecular techniques. This information will benefit plant scientists and breeders who are devising new strategies to improve disease resistance in plants as well as decrease the use of chemical pesticides and antibiotics.

Technical Abstract: Acetosyringone is a phenolic metabolite often found in plant apoplasts. Its oxidation by hydrogen peroxide and peroxidase results in a prolonged increase in the redox potential of the reaction mixture, similar to redox increases observed in suspension cells upon treatment with incompatible bacteria. Since high redox potentials, being oxidative, are generally detrimental to bacteria, the effect of oxidation of acetosyringone and other phenolics on bacterial viability was examined. Pseudomonas syringae pv. syringae was added to reaction mixtures containing acetosyringone, hydrogen peroxide and peroxidase and samples were removed to determine viability by dilution plating. Initial studies were done with low bacterial concentrations, 105 CFU ml-1, to ensure that scavenging of H2O2 was negligible and did not interfere with the reaction mixture. No colonies were formed by bacteria that had been added to reaction mixtures with acetosyringone ranging from 25 to 100''. Examination of the bacteria by microscopy and flow cytometry, using fluorescent stains that indicate bacterial viability and membrane integrity, suggested that these bacteria had maintained their membrane integrity. In addition they were able to respire based on oxygen uptake. When bacteria were added to on-going reaction mixtures at a time point after the prolonged redox response, the CFU ml-1 increased indicating that a stable reaction product was not responsible for the non-culturability bioactive effect. Other bacterial isolates, P. s. pv. tabaci and P. fluorescens, were less susceptible to the bioactive effect of the acetosyringone oxidation. Other phenolics were tested and had lesser degrees of bioactivity and in some cases reduced the bioactivity of acetosyringone oxidation. The ‘viable but non culturable’ (VBNC) state of the bacteria in this study is compared to that described for other medical and plant pathogens.