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PhD Thesis defense: Helena Lozano
Thursday, July 16, 2020 @ 11:00 am–1:00 pm
Electrical and topographical study of bacterial appendages at the nanoscale
Helena Lozano, Nanoscale bioelectrical characterization group
Some bacteria can exchange electrons with non-soluble electron acceptors, such as minerals. This phenomenon is called Extracellular Electron Transfer (EET) and it can be done through several mechanisms, especially through conductive bacterial nanowires.
The main objective of this thesis is the investigation of the polarization properties of electrochemically active bacteria and their appendages. Specifically, I have studied two types of bacteria, Shewanella oneidensis MR-1 and cable bacteria. I have used the Electrostatic Force Microscopy (EFM), which measures the electrostatic force using a nanometric probe, combined with finite element simulations to obtain the polarization properties. The electrostatic force depends mainly on the geometry and dielectric constant of the probe-sample system.
First, I have developed a way to obtain the dimensions of objects avoiding physical contact with the sample by measuring the electrostatic force. I have tested this technique on silver nanowires and bacterial flagella, optimizing the EFM technique to nanowire-like biological samples at the nanoscale. Afterward, I have studied S. oneidensis Outer Membrane Extensions (OMEs), responsible for the EET. I have obtained a low value of the dielectric constant (εOME=3.7±0.7). However, considering that the conduction mechanism of such OMEs is through electron hopping, where electrons are localized, these results do not contradict the literature.
I have also studied the cable bacteria, especially the fibers that are along this filamentous bacterium. The dielectric constant of the fibers was εr=7±1. This result is not compatible with the conductivity reported in the literature. Therefore, a core-shell model was proposed with a conductive core of h~10–20nm.
Subsequently, I have performed qualitative EFM measurements in liquid over living and rehydrated S. oneidensis bacteria.
Finally, I have performed macroscale measurements in living S. oneidensis using a microfluidic device that I designed, fabricated and characterized at the Denmark Technical University (DTU), Copenhagen. It was used to perform two-electrode impedance measurements.
In order to attend to the defense, you must send an email to the president of the Doctoral Commission of the Faculty of Physics (Dr. Eugeni Grauges Pous – vd.fisica.recerca@ub.edu) with a minimum notice of 48 hours and will be held via Microsoft Teams.
