Surface Interactions of Metal-Reducing Bacteria: Attachment and Cellular Appendages
This dissertation describes investigations of the interfaces between useful micro-organisms and solid surfaces, such as electrodes. Many types of microbes are ecologically important and can be technologically useful. Electrochemically active bacteria are particularly interesting, because of their ability to couple their metabolisms with inorganic devices. For electrochemically active bacteria to engage electrodes, they must localize around the electrodes and establish electrically conductive pathways. To understand the microbial interaction with conductive materials, we investigated both the attachment characteristics of bacteria to surfaces as well as the properties of cellular appendages, which can provide extracellular electronic conductivity.
We probed the electrical and mechanical properties of bacterial appendages with atomic force microscopy methods. The adhesiveness of Geobacter sulfurreducens cellular appendages was determined and compared against electrical conductivity and nanoscale morphology. The electron mobility of Geobacter sulfurreducens pili was validated with electrostatic force microscopy as well. Design principles for correlating atomic force microscopy measurements and optical microscopy are discussed.
The attachment of Shewanella oneidensis to surfaces was investigated by measuring the number of adherent cells on surfaces through a combination of direct fluorescence measurement, counting colonies formed from cells removed by sonication, and microscopy of the bacteria-attached surfaces. More S. oneidensis cells attach to hydrophobic surfaces and mannosylated surfaces compared to bare gold.
Using mannose-decorated glycopolymers to functionalize gold surfaces, we stimulated S. oneidensis bacterial colonization, enriched the wild-type strain of the bacteria against ΔmshA-D knockout strain during co-deposition, and induced where bacteria attach on a molecular pattern. Vibrio cholerae was also directed to a molecular pattern. The three-dimensional multivalency of the glycopolymers enhanced the persistence of attached bacteria on the surface more than surfaces functionalized with a single glycoside per molecule. Removing the attachment enhancement required equilibration between methyl α-D-mannopyranoside competitor and the cell culture. This requirement suggests the retention of cells on glycopolymer surfaces is kinetically controlled, and not a thermodynamic result of the cluster glycoside effect. Our findings, that the surfaces we studied can induce stable initial attachment and influence the ratio of bacterial strains on the surface, may be applied to harness various useful microbial communities.