Intraspecies Variation of Xanthomonas citri Biofilm Formation

Hibberd, Sophie (2021) Intraspecies Variation of Xanthomonas citri Biofilm Formation. Masters by Research thesis (MSc), Manchester Metropolitan University.

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Abstract

Prevalent in citrus growing regions worldwide, Xanthomonas citri (XCC) is a phytopathogen capable of causing significant economic losses due to the disease which is causes; Citrus Canker. Mechanisms of combatting the disease have focused on eradication of infected trees or prevention using non-specific bactericides, including copper, both options can result in wider harm to the environment and economy. Bacteriophage are a novel treatment option which holds promise of being a successful treatment option with no undesirable effects on the winder environment due to their specificity of infection. However, X.citri forms complex biofilms, meaning further understanding of both the biofilm phenotype and the ability for phage to infect are required. Using crystal violet biofilm assays to assess the growth of 93 bacterial isolates, this study aims to assess intraspecies variation of biofilm phenotype. Additionally, 25 bacteriophage were purified and assessed for host range infectivity along with efficacy in eradicating a mature (48 hours) biofilm using 20 bacterial isolates, selected for biofilm formation and geographical location, using crystal violet assay and CFU/Ml. Results demonstrate a wide variety in biofilm forming abilities, with 41 isolates being labelled ‘high density biofilm producers’. Once treated with bacteriophage, 45% of isolates exhibited statistically significantly decreased biofilm formation when assessed by crystal violet assay, all isolates showing this decrease originated from the São Paulo state of Brazil. However only 10% showed the same decrease when observing CFU/Ml. Overall this study shows promising data for the potential of treating citrus canker infections in São Paulo with bacteriophage however further studies are required to compare this to the possible preventative use of bacteriophage and to establish the efficacy in the epiphytic conditions of the disease, for example when grown on orange peel.