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Molecular interactions between bacteria and eukaryotic hosts

The health and wellbeing of plants, animals and humans is to a large extent determined by the microbes with which they co-exist. Some bacteria are pathogens causing diseases, but many others enhance growth and confer disease resistance. 

Photo of bacterial cells (Pseudomonas aeruginosa) taken by Scanning Electronic Microscopy (SEM) *Niki Murray and Xue-Xian Zhang

A graphical abstract from the research project showing the molecular interaction between the bacteria and its host.

This project uses modern tools in molecular biology to elucidate the mechanisms of bacterial colonisation on the surfaces of plants and human tissues. 

Nutrient utilisation

Bacteria have strict food preferences in terms of the order in which they uptake and utilise substrates: the underlying mechanism being carbon catabolite repression (CCR). CCR has been well studied in E. coli where it is mediated by the catabolite-activating protein (CAP) charged with cAMP. However, this paradigm does not hold for many non-enteric bacteria such as Pseudomonas fluorescens SBW25. SBW25 is a plant growth-promoting bacterium isolated from sugar beet leaves grown in Oxford University farm. It belongs to the same genus of Psa, the causative agent of kiwifruit bacterial canker. We found that SBW25 has evolved a very complex CCR mechanism to ensure preferential utilization of nutrients that coexist in the environments. Such knowledge will help understand how bacteria are fed in planta, and develop new methods such as the use of toxic nutrient analogues to control plant infectious diseases.

Targeting the mechanism of host recognition to prevent bacterial infections

With the widespread increase of bacterial resistance to antibiotics, new strategies to prevent and treat healthcare-associated infcetion (HAI) are urgently required. This project funded by the Auckland Medical Research Foundation (AMRF) addresses a crucial gap in our current understanding of how bacteria cause disease – namely, how pathogenic bacteria recognise vulnerable hosts for successful colonization and immune evasion.

To date, our research has focused on Pseudomonas aeruginosa, an environmental pathogen that causes a wide range of healthcare-associated infections and pulmonary infections in people with chronic lung diseases, particularly cystic fibrosis. We are testing a new hypothesis that P. aeruginosa recognises urocanate, a histidine metabolite accumulated in tissues such as skin, and use it as a trigger for bacterial invasion. The data will form the basis for the development of new strategies to prevent bacterial infection through interrupting the urocanate-mediated host recognition.


  • Associate Professor Xue-Xian Zhang

    Associate Professor Xue-Xian Zhang

    Associate Professor in Molecular Cell Biology
    - School of Natural Sciences

    My primary expertise is in Molecular GeneticsMicrobiology. Current research in my lab focuses on:

    • The molecular mechanisms of bacterial adaptation to their natural environments, i.e. plant and soil;
    • Developing microbiological knowledge and technology to mitigate nitrate pollution of water from agriculture;
    • Enhancing the efficacy of copper bactericides for controlling the bacterial canker disease (Psa) in kiwifruits.