Xanthomonas citri subsp citri citrus tree cankers in Sao Paulo : molecular epidemiology and assessment of lytic bacteriophage as biocontrol agents

Asiatic Citrus Canker (ACC) is a serious, untreatable infection of citrus trees that threatens sweet orange production in the state of Sao Paulo - a key industry economically. ACC is caused by the bacterium Xanthomonas citri subsp. citri. Infection with this organism necessitates removal and destruction of infected trees and prevention measures typically rely on the use of spraying with environmentally harmful copper bactericides. In this project we will examine the current genetic diversity and molecular epidemiology of X. citri from infected plants in Sao Paulo using whole genome sequencing. This will allow us to study how the pathogen is spreading in the current endemic situation - following legislative changes that ceased control efforts and now allow the presence of the bacterium in the orchards. This information will give us important new knowledge regarding the species population biology.

In this project we will also isolate and characterize X. citri specific viruses (known as bacteriophage). Bacteriophages are proposed as an alternative to antibiotics in human health and they are currently used in the food industry eg for controlling Listeria contamination in cheese production. They are also used in the control of bacterial infections in tomato and pepper crops in the United States. We will isolate and characterize a large collection of bacteriophage from infected plant material to assess their suitability for use in biocontrol of ACC. This initial pump-priming proposal will be developed in years two and three to include in vitro infection studies in greenhouse using bacteriophages as treatments or protective agents. We will also investigate bacteriophage host-binding structures as possible species-specific ligands for delivery of antimicrobial compounds.

Who will benefit from this research and how will this happen?

Asiatic Citrus Canker (ACC) is a severe and untreatable disease of citrus trees that represents a major ongoing threat to sweet orange production in São Paulo - an industry that employs around 200 thousand people in the state. In this study we will examine the epidemiology of this endemic disease by studying genomic and population diversity within the bacteria that causes this disease - Xanthomonas citri subsp. citri (X. citri). Knowledge of the diversity of the pathogen population across São Paulo will help us select lytic bacteriophages for potential use as species-specific, environmentally sustainable biocontrol agents to target ACC infections.

People whose livelihoods depend on the sweet orange production industry in São Paulo will be the primary beneficiaries of this research but it will also greatly help members of Dr Ferreira's and Prof Enright's research groups particularly those directly engaged with the project. The project will also benefit scientists interested in plant-microbe interactions, microbial genomics and bacteriophage biology through the timely dissemination of large amounts of novel genomic sequences from bacterial and lytic bacteriophage sequencing and associated metadata. Although this is a one year project we are confident that enough new information will be gained in this initial pump-priming phase that we will have sufficient data to publish selected novel data in a high-quality open access journal within a few months of project completion.