In order to fight hunger and meet the food demands of a constantly growing human population, drastic changes need to be introduced in the agricultural sector. To achieve that in a sustainable manner, current agricultural practices should be improved and the negative impact caused by the overuse of fertilizers and pesticides on the environment reduced. A promising solution to this problem could be a cell-based delivery system, which takes advantage of the natural targeting properties of a living organism, such as bacterium, and combines it with the benefits of using polymer nanoparticles to encapsulate and deliver a cargo to the desired target in a controlled manner. Such a bio-based hybrid system could potentially improve the crop growth and reduce the negative effect of agrochemicals on the environment. The use of nanoparticle-decorated bacteria as targeted hybrid delivery systems has been shown in the literature before with great emphasis put on the medical field, for example to combat cancer. The goal of this thesis is to evaluate the potential of using nanoparticle-modified plant beneficial bacteria for agricultural applications. Chapter 1 explains the motivation behind this work and the goals of the study, while Chapter 2 provides an overview of the recent literature highlighting the research done in the field of nanotechnology for agricultural purposes, the application of plant growth promoting bacteria in agriculture and the use of nanoparticle-modified bacteria as vectors for the targeted drug delivery. Chapter 3 studies the correlation between different conjugation strategies and the attachment efficiency of polymer nanoparticles to the surface of two plant-beneficial bacterial strains. A library of bacteria-nanoparticle hybrids is produced and characterized using confocal microscopy, super resolution microscopy and flow cytometry.
Chapter 4 evaluates the influence of polymer nanoparticles with various chemical functionalities and concentrations on bacterial growth and assesses the impact of the nanoparticle attachment on the viability of bacteria. This chapter also studies the effect of nanoparticle attachment on the growth and division of single cells. Chapter 5 shows the initial studies of the movement of nanoparticle-bacteria hybrids. In the second part, this chapter focuses on the development of a chemotaxis assay for studying the ability of plant-beneficial bacteria to migrate towards plant chemoattractants.