Synthesis and characterisation of graphene oxide and its impact on soil bacteria

Carbon based materials such as graphene have recently been widely studied. Graphene oxide (GO) is a member of the graphene family with functional groups which make it hydrophobic, thus making it useful for many applications such as an antibacterial agent. However, there is controversy in the literature about the effect of GO on bacteria. Therefore, it was important to prepare a highly purified GO using Hummers’ method and characterise it before studying the biological test. The final product shows that GO had 1-2 layers with oxygen group on the GO sheets. Bacteria are often found in nature in a form called biofilms. Bacterial cells are embedded in an extracellular matrix composed of polymers. This protects bacteria from harmful factors such as antibacterial agents more than planktonic (free) cells. In this study, the objective was to study the effect of GO on soil bacteria. GO was prepared and characterised using optical and surface techniques. Then GO was applied to two species of bacteria found in soil, Pseudomonas putida and Acinetobacter sp., in biofilm and planktonic forms. It was found that biofilms showed more susceptibility to GO than planktonic cells. Moreover, the antibacterial effects of GO on biofilms depended on the maturity stage of the biofilm. The impact of GO and environmental stresses (temperature, pH and NaCl) on P. putida was examined. It was found that environmental conditions changed the susceptibility of biofilm to GO. Moreover, it was found that the removal of EPS from biofilms increases the susceptibility to GO. Finally, it was found that GO changed the chemical compounds of the cell wall.