In light of this scenario, the present work proposes the selection of a microbial consortium from cow dung and the study of the formation and growth of an ureolytic biofilm on graphite surfaces by Electrochemical Impedance Spectroscopy (EIS) without noticeable modifications of the biofilm. EIS spectra were obtained at open circuit potential (OCP) (without additional electric perturbation apart from sinusoidal perturbation ±10 mV), during the time of immersion of graphite in the culture medium, in the absence (Control) and presence of bacteria (Biotic).
The results (figure 1) indicate that the spectra of both control and biotic conditions exhibit just one time constant. Moreover, spectra adjustment to equivalent electric circuits indicates that the biofilm adhesion is directly related to the modification of the capacitance, while the generation of ammonium ions directly influences the decrease in electrical resistance of the culture medium. The biofilm maturation and its interaction with the graphite surface induces lower charge transfer resistance, which can be applied as a novel technology for the urea hydrolysis. SEM and CLSM images confirm the presence of ureolytic biofilm and confirm the interpretations obtained by EIS.
Figure 1. Evolution of Bode plots obtained on a graphite surface (0.283 cm2) during the time of immersion. Solid symbols identify frequency where the impedance was obtained. The lines are simulated EIS diagrams constructed with the electric parameter values obtained from the best fit of EIS experimental spectra. The study systems: a) and c) Control (without bacteria), and b) and d) Biotic: with microbial consortium inoculum.
Funding
This research was supported by the National Council for Science and Technology (CONACyT) México and for the scholarship 328072.
References
- J. M. Connolly, B. Jackson, A. P. Rothman, I. Klapper, and R. Gerlach, npj Biofilms Microbiomes, 1, 15014 (2015) http://www.nature.com/articles/npjbiofilms201514.