SR-FTIR Study of Bacteria-Water Interactions: Acid-base Titration and Silification Experiments

Bacterial surfaces are highly reactive and can strongly affect mass transport in a wide range of geological environments. Bacterial cell walls can adsorb aqueous metal cations, and can act as nucleation surfaces for heterogeneous mineral precipitation. However, the reactions at the bacteria-water interface are poorly understood, primarily due to the difficulty in monitoring such processes in situ and in vivo. In this study, we use synchrotron radiation-based FTIR to investigate the chemistry of bacterial surfaces with acid/base titration and Si precipitation experiments. The objectives of this research are to identify the reactive surface functional groups and to determine how metal adsorption/precipitation affects the protein and lipid structures of individual living bacterial cells. In-situ FTIR experiments were performed on the Infrared beamline 1.4.3 at the Advance Light Source (Lawrence Berkeley National Laboratory), using a Nicolet 760 FTIR bench and a Spectra-Tech Nic-Plan IR microscope. All experiments were performed with flow through fluid cell with BaF2 and ZnSe windows separated by a 6 um mylar spacer. Acid-base titration and Si precipitation experiments were conducted with both intact cells and isolated bacterial sheaths of Calothrix (strain KC97) a filamentous cyanobacteria. Titration experiments with intact bacterial cells show a change in peak position of the carboxylic functional group at ~1400 cm (symmetric vibrational stretching of deprotonated carboxylate groups) from acidic to near-neutral pH (Fig 1). The bacterial silicification experiments indicate a change in peak position at ~ 1700 1740 cm, corresponding to the vibrational C=O stretching of esters groups in the lipid structures of the cell (Fig 2). Previous studies have demonstrated that hydrogen bonding onto carbonyl functional