Biospectroscopy diagnosis of bacterial interaction with environmental molecules

Aims: Bacteria are universal micro-organisms that can be found in almost all aquatic and terrestrial environments and strongly affect ecological systems at different spatial scales. The activities of bacteria are profound on the physicochemical features of natural environments, while natural environments shape bacterial behaviours through physical and chemical alterations. Different molecules present in the environment produce significant effects on bacteria. Therefore, it is required to study the rich and complementary interactions between bacteria and molecules. In this thesis, four research studies were conducted to investigate the interactions between bacteria and nanoparticles or carbonaceous substrates, deploying state-of-the-art techniques which can yield new insights. Methods: Raman micro-spectroscopy was employed in this thesis as a diagnostic tool to detect the biochemical alterations of bacteria post-exposure to different chemical molecules. Unlike conventional methods, such as light/electron microscopy, molecular analysis techniques and bacterial behaviour assays, Raman spectroscopy provides detailed information of biological constituents of bacteria that interact with diverse molecules. In addition, computational analysis including principal component analysis and linear discriminant analysis (PCA and LDA) was used to process the Raman spectral data. Results and Discussion: Raman spectra characterize the interaction between bacteria with different molecules. Spectral characterization showed the specific binding of nanoparticles with nucleic acids and amino acids in bacteria, and the different chemotactic behaviours of bacteria towards carbohydrates, organic acids and alkanes. Distinct spectral alterations allowed the evaluation of the alkane affinity in bacteria, and enabled quantification of the concentrations of glucose or organic acids in the aquatic phase. Furthermore, computational analysis of spectral alterations illustrated the effects of nutrient cations on alkane affinity in bacteria, and indicated the selective affinity of bacteria towards different organic carbonaceous molecules in the mixture of carbonaceous substances. Findings from this thesis showed that Raman spectroscopy is a rapid, reliable and non-destructive approach to investigate the interaction of bacterial cells with diverse molecules, which implies techniques involved in Raman spectroscopy can diagnose subcellular changes both in situ and in vivo post-exposure to different natural conditions or chemical molecules