Modulation of Curli Production on Redox Challenged PEDOT:PSS Surfaces

Biofouling is a major problem caused by bacteria colonizing abiotic surfaces, such as medical devices. Biofilms are formed as the bacterial metabolism adapts to an attached growth state. We have previously found that electrically charged surfaces with high charge storage capacity like PEDOT-based conducting polymers can be used to modulate the amount of gross biomass attaching by altering the surfaces redox state(<i>1</i>).<br/>Here, we are delivering an in-depth analysis on the process of biofilm formation on redox-challenged PEDOT: PSS surfaces. We are using GFP tagged <i>Salmonella</i> bacteria and a marker for the <i>Salmonella</i> extracellular matrix components curli and cellulose (EbbaBiolight 680) to decipher the relationship between the amount of bacterial cells and extracellular matrix produced by bacteria in <i>Salmonella</i> wt bacteria as well as mutants deficient in curli (ΔcsgA) or curli as well as cellulose (ΔcsgD)(<i>2</i>). We are using a semi-quantitative spectroscopy method to determine relative amounts of bacterial cells and extracellular matrix (ECM) on a large surface area and are performing detailed microscopic analysis to understand biofilm distribution and structure.<br/>When the redox challenge was carried out in a fast-charging whole-cell setup, higher amounts of cells and ECM were found on oxidized PEDOT:PSS surfaces compared to their reduced counterpart. When electrodes were separated and charging was carried out with respect to a Pt electrode, the charging process was slower and incomplete. This resulted in almost similar cell numbers for the two cases but showed much higher amounts of ECM on reduced surfaces. A curli mutant, grown under the same conditions produced biofilms that didn’t respond to the redox challenge. The microscopic structure of the biofilm showed uniform cell and ECM distribution on all oxidized surfaces but showed high-density local clusters of around 100-200 µm diameter on all unchallenged and reduced surfaces.<br/>This leads us to believe that redox modulation of biofilm formation mainly depends on curli production. We forward a theory where an oxidized PEDOT:PSS surface works as an alternate terminal electron acceptor for interfacial biofilm, which might be able to boost ATP production and curli formation. We reason that the negative charge of PEDOT:PSS on unchallenged and reduced surfaces leads to a spotty attachment of the bacteria and to the formation of microcolonies, instead of evenly distributed films.<br/>References<br/>1. S. Gomez-Carretero, B. Libberton, K. Svennersten, K. Persson, E. Jager, M. Berggren, M. Rhen, A. Richter-Dahlfors, Redox-active conducting polymers modulate Salmonella biofilm formation by controlling availability of electron acceptors. <i>NPJ Biofilms Microbiomes</i>. <b>3</b> (2017), doi:10.1038/s41522-017-0027-0.<br/>2. F. X. Choong, S. Huzell, M. Rosenberg, J. A. Eckert, M. Nagaraj, T. Zhang, K. Melican, D. E. Otzen, A. Richter-Dahlfors, A semi high-throughput method for real-time monitoring of curli producing Salmonella biofilms on air-solid interfaces. <i>Biofilm</i>. <b>3</b> (2021), doi:10.1016/j.bioflm.2021.100060.