The bacterial cell wall is a nearly universal structure that offers protection and gives the cell its shape. However, environmental stressors, such as cell wall-targeting antibiotics and... Show moreThe bacterial cell wall is a nearly universal structure that offers protection and gives the cell its shape. However, environmental stressors, such as cell wall-targeting antibiotics and hyperosmotic conditions, can induce bacteria to shift to a wall-deficient state. It is unknown whether the lack of this cell wall ‘barrier’ can enable DNA exchange via horizontal gene transfer (HGT), a process that facilitates the spread of antibiotic resistance amongst bacteria. The research in this thesis confirms that wall-deficiency enables HGT in the actinobacterium Kitasatospora viridifaciens. Specifically, we show that wall-deficient L-forms take up extracellular material including DNA, sugar polymers and lipid nanoparticles via an endocytosis-like mechanism, which in case of DNA uptake leads to genetic transformation. Moreover, wall-less cells exchange genomic DNA in a DNAse-resistant manner, most likely via cell-cell fusion and/or production of extracellular vesicles. We also isolated vesicle-producing actinobacteria from a wastewater treatment plant, an environment that is considered a hotspot for the spread of antibiotic resistance genes. Lastly, growth of K. viridifaciens under hyperosmotic stress conditions leads to genetic instability, which together with HGT can contribute to enhanced genome plasticity. In summary, this thesis provides important insights into the consequences of bacterial cell wall-deficiency for HGT and evolution. Show less
With the rise of multi-drug resistant bacterial pathogens, the possibility of a post-antibiotic world is quickly becoming reality. It is therefore vital that research is focussed on overcoming the... Show moreWith the rise of multi-drug resistant bacterial pathogens, the possibility of a post-antibiotic world is quickly becoming reality. It is therefore vital that research is focussed on overcoming the most challenging bacterial resistance mechanisms. To this end, the aim of the work described in this thesis was to develop novel strategies to combat resistant bacteria, with particular focus on the threat posed by gram-negative bacteria. Show less
