Raman Microscopic Studies on Accumulation of Pullutants by Biofilms in Aquatic Systems

Objectives

• Development of nondestructive technology for chemical characterisation of biofilms in the µm-range
• Application of ¹³C tracers for studies on pollutant accumulation
• Analysis of interactions of biofilms with different iron phases

Methods of Approach

• Raman Microspectroscopy
• Reactor for biofilm growth

Description

It is now widely recognized that in natural environment microbial cells are most often found in close association with interfaces in the form of biofilms. Biofilms are the communities of microorganisms embedded in a matrix of extracellular polymeric substances (EPS, biopolymers such as polysaccharides, proteins, nucleic acids, lipids, and humic-like substances). In aquatic systems the biofilms may have a significant impact on the flux and fate of water quality-related substances. Since biofilms are very sensitive to varying boundary conditions, a rapid analytical tool for chemical characterization with high spatial resolution and sensitivity is required. Raman Microspectroscopy (RM) is a nondestructive technique which provides in situ whole organism vibrational fingerprints for (micro)biological samples in the µm-range. Nevertheless, the Raman efficiency and therefore the RM sensitivity is rather limited. However, the Raman effect can be significantly enhanced if a molecule is attached to, or in immediate proximity of a nanometer-roughened metal (e.g. Ag, Au or Cu) surface. This technique, known as Surface-Enhanced Raman Scattering (SERS), results in enhancement factors in the range of 10³ – 10⁶ (under certain conditions up to 10¹¹) due to the electromagnetic and chemical enhancements.

In this project we plan to analyze the impact of different dynamics on growth rate and the accumulation/degradation of water quality-related substances (dissolved and colloidal matter) by biofilms. Firstly, the effects of i) different substrates and their concentrations, ii) various flow rates, iii) age of the biofilms and iv) fluctuations in geochemical conditions (ionic strength, pH, etc.) will be studied by RM and SERS. For better understanding of degradation pathways, stable-isotope RM will be employed. The incorporation of ¹³C tracers into biofilms during cultivation should cause significant changes (key red-shifted peaks) in Raman spectra of microbial cells and other biofilm constituents. Secondly, the influence of biofilms on the transport of colloidal particles has to be studied. Here, the high sensitivity of RM to e.g. different iron phases will enable to assess their interactions with biofilm matrices. The results should help to understand the influence of biofilms on the processes at compartment interfaces and hence on the flux, turnover and fate of natural and anthropogenic pollutants in regional water cycles.