Silvia Simison

Metabolic turnover and catalase activity of biofilms of Pseudomonas fluorescens (ATCC 17552) as related to copper corrosion

In this work we report the results of a combined biochemical and electrochemical study aimed to analyze both the growth of biofilms of Pseudomonas fluorescens on copper samples and its possible role in the instability of the metal/electrolyte interface. DNA and RNA were quantified along the time for biofilms grown on copper and glass to estimate both the growth of the bacterial population and its metabolic state (through the RNA/DNA ratio). The expression and specific activity of catalase were also determined to gain insight into their possible role in corrosion acceleration. The electrochemical behavior of the biofilm/copper interface was monitored by Linear Polarization Resistance (Rp) and electrochemical impedance spectroscopy (EIS) along the experiments. Results showed a longer lag phase for biofilms developing on copper that included a period of high metabolic activity (as measured by the RNA/DNA ratio) without biomass growth. Biological activity introduced a new time constant at intermediate frequencies in EIS spectra whose capacitive behavior increased with the biofilm development. The increment in this biofilm-related signal was accompanied by a strong limitation to charge transfer through a diffusion controlled process probably due to oxygen exhaustion by cells respiration, while the resistance of the interface decreased presumably due to oxide dissolution by local acidification under the colonies. In addition, catalase activity was found to be high in mature copper-tolerant biofilms, which differentially express a catalase isoform not present in biofilms growing on glass.

Biochemical Capacitance of Geobacter Sulfurreducens Biofilms

An electrical model able to decouple the electron pathway from microbial cell machinery impedance terms is introduced. In this context, capacitance characteristics of the biofilm are clearly resolved. In other words, the model allows separating, according to the advantage of frequency and spectroscopic response approach, the different terms controlling the performance of the microbial biofilm respiratory process and thus the directly related electricity production process. The model can be accurately fitted to voltammetry measurements obtained under steady-state conditions and also to biofilm discharge amperometric measurements. The implications of biological aspects of the electrochemical or redox capacitance are discussed theoretically in the context of current knowledge with regard to structure and physiological activity of microbial Geobacter biofilms.