UC Santa Barbara

Microorganisms like bacteria have evolved over billions of years to survive in diverse environments and have developed unique functions and metabolic pathways as a result. Manipulating and harnessing their abilities has been a hallmark of the biotechnology revolution and has the potential to solve problems in areas as diverse as health, environmental remediation and energy production. With genetic engineering we now have the ability to install in microbes beneficial functionalities and chemical production processes, but have really just scratched the surface of what is possible. Truly disruptive innovations will come from controllably interfacing these microscopic workhorses with non- living systems in an effort that will likely require both genetic engineering and materials science approaches.

It is with this premise that I present my research on a class of synthetic small molecules known as conjugated oligoelectrolytes (COEs). These water-soluble oligomers spontaneously intercalate into biological membranes and in turn modify the ionic and electronic transport properties of this ubiquitous interface in a variety of microorganisms.

COEs have previously been shown to improve the performance of microbial electronic devices for power production and contaminant removal in wastewater. The research presented here demonstrates the use of COEs for the inverse process of powering a microbe, Shewanella, in order to drive metabolic activity, specifically the reduction of fumarate to succinate. A mechanistic investigation of this process utilizing various voltammetry techniques, microscopy, liquid chromatography, and visible spectroscopy reveals possible membrane permeabilization and enzyme excretion, contradicting a previous hypothesis of COEs acting like transmembrane “molecular wires.” In addition, structure-function relationships for COEs are developed through examination of the effects of different molecular features on various biological systems. Using microscopy and electrochemistry, some effects of ionic group type and arrangement on the biological interactions of COEs are revealed. It is determined that cationic charges are necessary for interaction with E. coli and that a terminal end-only arrangement of charges is beneficial for lipid membrane intercalation. Finally through visible spectroscopy and zeta potential measurements it is determined that longer COEs associate in less quantity with E. coli but affect the cell surface charge to a greater degree than do shorter COEs. It is these relationships that will ultimately lead to new biological applications and inform future molecular design of this exciting class of molecules.