Cell concentrations and metabolites enhance the SIP response to biofilm matrix components

Abstract

We investigated the relative effect of different bacterial biofilm components to influence spectral induced polarization (SIP) signals and Cole-Cole model parameters (i.e. normalized chargeability (S m−1) and relaxation time (τ)) in order to reduce the ambiguity associated with interpretation of SIP signatures in biostimulated environments. SIP measurements were collected over a frequency range, (i.e. 0.1 Hz–1 kHz) from experimental columns containing Pseudomonas aeruginosa PAO1 (non-mucoid bacterial strain) cell suspensions alone and cell suspensions mixed with different molecules associated with P. aeruginosa biofilm matrix (alginate, DNA and phenazine). Results from SIP measurements of cell density investigations suggest an increase in phase (~ 200%), imaginary conductivity (σ″ S m−1), and normalized chargeability (S m−1) values as cell densities increase (1.50–5.55 × 109 CFUml−1), yet no significant change in the real conductivity (σ′ S m−1) or relaxation time was observed. The addition of alginate resulted in a suppression of phase (φ mrads), imaginary conductivity (σ″ S m−1), and normalized chargeability (S m−1) response. However, a mixture of cells and alginate increased all parameters but with no significant changes in real conductivity (σ′ S m−1) or relaxation time. Similar trend was observed in the DNA treatments; increasing concentrations of DNA reduced the imaginary conductivity (σ″ S m−1), phase (φ mrads), and normalized chargeability (S m−1) response. In contrast, the addition of phenazine, a secondary metabolite of P. aeruginosa, resulted in a significant increase in both imaginary conductivity (σ″ S m−1), phase (φ mrads), and normalized chargeability (S m−1) values especially at larger concentrations (>50 mM). Our work suggests that cell density and metabolites are significant factors increasing the polarization response in biofilms and advances the interpretation of electrical signals associated with biofilms in the subsurface.