Exploratory Analysis of Bacterial Raman Spectra in Electroactive Biofilms

Wednesday, 31 May 2017: 16:20
Durham (Hilton New Orleans Riverside)
N. Lebedev, S. Strycharz-Glaven (Naval Research Laboratory, CBMSE), and L. M. Tender (Naval Research Laboratory)
Bacterial electroactive biofilms attract researchers’ attention due to their ability for generation of electric current when electrons travel for very long distance, up to several tens microns in the course of cell metabolic activity. It was demonstrated that this electron transfer (ET) ability correlates with the accumulation in the BF huge amounts of a c-type cytochrome (Cyt), but molecular nature of this Cyt, its spatial localization, interaction with the environment, regulation and the controlling factors are not completely understood. Raman spectro-electrochemical analysis is a very useful tool for nondestructive spatially-resolved in vivo study of ET mechanisms. But utilization and especially interpretation of Raman spectra requires deep understanding of their origin. Traditional approach to interpret Raman spectra is based on an assignment of specific Raman bands to the vibration of individual chemical bonds. Though some interesting results and conclusions were made using this approach, especially for small molecules, it does not allow for mapping Raman spectrum to complex organic and biological molecules like Cyt. Moreover, we and others have shown that most of Raman spectral bands of biomolecules are due to collective oscillation of several chemical bonds that requires another means of spectral description. This problem can be solved by computer simulation of Raman spectra allowing for identification of their structural origin and project/map them to molecular structure at sub molecular spatial resolution. This opens up the possibility of wise analysis of molecular interaction of individual biomolecules and their components. Spectroscopic analysis of more complex multi-structural and multicomponent biological systems, like biological cell and biofilms is often so complex that detection and separation of individual bands is very difficult to achieve. This problem can be solved by Principal Component Analysis (PCA) allowing for data squeezing to smaller number of the main, so called principle, components (PCs). Prescribing these PCs to specific classes of molecule allows for classification and comparative analysis of complex systems. In this presentation we will summarize our results on the application of Exploratory Confocal Raman Spectroscopic Analysis for identification of the main ET components (structure-functional relationship) in bacterial Raman spectra and organization of these ET components in multifunctional and multidimensional bacterial anodic and cathodic electroactive biofilms. We will show how interaction of the cells with inorganic substrates affects their metabolic activity; how cells talk to each other about that; and how electron transfer through an individual bacterial cell can be monitored.