Unravelling the molecular and evolutionary mechanisms of copper resistance in plant-associated Pseudomonas spp. : Master Thesis, School of Natural Science, Massey University, Auckland, New Zealand
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2024
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Massey University
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Copper (Cu) is a vital trace element for all living organisms but can be extremely harmful when in excess. Its antimicrobial properties have made copper compounds a popular choice in agriculture for managing plant diseases. However, the widespread use of copper-based bactericides has resulted in heavy metal pollution and the emergence of copper-resistant strains, which could potentially undermine disease control efforts. The mechanism by which copper inhibits pathogenic infection, the capacity of pseudomonads to evolve copper resistance, and the potential for co-evolution of resistance to copper and antibiotics are yet to be evaluated. Furthermore, the impact of the evolution of copper resistance on bacterial virulence remains a mystery. The central objective of my research project was to unravel the molecular and evolutionary underpinnings of copper resistance in pseudomonads, a group of bacteria that are closely associated with plants. This includes the study of Pseudomonas fluorescens SBW25, which is a model bacterium known for promoting plant growth. Additionally, my project also focused on Pseudomonas syringae pv. actinidiae (Psa) NZ13 and NZ47, the causative agent of bacterial canker in kiwifruit. By understanding the mechanisms of copper resistance in these bacteria, we can gain insights into how they adapt to environmental stressors, which could have significant implications for agricultural practices and disease management. In this work, I successfully devised a strategy to quantify bacterial infection using lux labelled bioreporter strains. This innovative technique has shed light on the inhibitory action of copper on kiwifruit infection by Psa. This newfound understanding of copper’s inhibitoryeffect can contribute to the sustainable use of copper bactericides in agriculture. Furthermore, my research has confirmed that prolonged exposure to copper can lead to the emergence of copper resistant pseudomonad strains. Interestingly, I found that resistance to aminoglycosides appears to co-evolve with copper resistance, particularly in strains derived from P. fluorescens SBW25. My work also provides insights into the potential roles of two-component regulatory systems (CopRS and EnvZ-OmpR) and transcriptional regulators (HutC and KefA). They may act as global regulators in copper resistance, antibiotic resistance, and Psa virulence. This understanding could pave the way for new strategies in managing bacterial diseases and promoting sustainable agriculture.