Examining biofilm growth and metabolism of Escherichia coli at laboratory scale using geoelectrical methods
To link geophysical field data to specific biological phenomena, controlled laboratory experiments are needed for the understanding of the response of geophysical parameters to changes in biological conditions. In this study, suspensions of bacteria were mixed with sand to create a biofilm growing on a surface and these mixtures were monitored using the geoelectrical spectral induced polarization method (SIP). The beginning growth of the biofilm was confirmed by scanning electron microscopy and the amount of bacteria in liquid and sand estimated using culture and DNA based methods (i.e. qPCR, quantitative polymerase chain reaction). While changes in SIP signal could not be clearly related to microbial activity, fluctuations in the phase shift were concomitant with the detection of two unidentified metabolites in the liquid extracted from the sand. These metabolites were only detected when the biofilm was produced under oxygen limiting conditions. Even though the experimental design was not optimal for the SIP measurements, the results support the idea that these measurements are not measuring cell mass but are influenced by the presence of smaller charged molecules that may be produced as microbial metabolites. As microbial metabolites would change in the field during bioremediation, this method could be applied for this type of monitoring.