EVOLUTION OF ANTIMICROBIAL RESISTANCE: BIOTIC AND ABIOTIC FACTORS AS DRIVERS OF NATURAL TRANSFORMATION

To survive environmental stressors, such as DNA damage and the presence of antibiotics, bacteria have developed a mechanism of natural competence, leading to the acquisition of beneficial exogenous genes through natural transformation. Natural transformation is an understudied horizontal gene transfer mechanism which plays an important role in the transmission and dissemination of eDNA in natural bacterial populations, providing a source of genetic diversity. Whilst this is a source of diversity, there is a concern on how this mechanism may increase the prevalence of antimicrobial resistance in environmental bacteria. In addition, there are some key environmental bacteria that have not yet been documented to be naturally transformable, such as Escherichia coli, and its currently unknown whether biotic and/ or abiotic stressors, such as the presence of competitors and availability of nutrients, can influence the natural transformation frequency. In this study, environmentally sampled E. coli strains were tested to see if they were naturally transformable. Then, using a model species system with Acinetobacter baylyi, transformation frequency was assessed following exposure to the presence of different competitor species or altered nutrient concentration, with and without the addition of extracellular peptide filtrate. Recent literature suggests that more species are capable of undergoing a competent state, and initial evidence has been generated here to support the ability of E. coli to perform natural transformation. However, further testing and replication are now required to understand and support this fully. Further, this work found that nutrient availability and the presence of certain competitor species have a significant effect on natural transformation efficiency. Given that bacteria are extremely evolvable depending on their surrounding environment, it is crucial to understand the evolutionary drivers of mechanisms such as natural transformation and thus, reduce potential threats of environmental AMR emergence to One Health systems.