Microbial exoelectrogens present promising avenues for the development of bioremediation, biofuel cells and synthetic biology. Our research interests are focused on achieving efficient electron transfer from these organisms embedded in biohybrid constructs while reducing ohmic loses in the system. A crucial aspect for attaining this goal is to fully understand bacterial motility and attachment to the solid support of interest in which respiration occurs. Therefore, biofilm formation is of central interest in anode respiring microorganisms relying on extracellular electron transfer (EET). Microbial appendages have been proposed to be involved in cell attachment as well as in different modes of cell motility prior to the biofilm formation process as observed in select microorganisms [1]. Amongst them, Shewanella oneidensis has been thoroughly used as a model for further understanding microbial electrochemical phenomena. A crucial area of study contributing to the development of microbial electrochemical systems consists in identifying key components involved in the assembly and functionality of pili and flagella in this organism.

Therefore, in this study we utilized motility mutants of S. oneidensis MR-1 that lack key proteins involved in the secretion of type IV pili and flagella. Electrochemical techniques were explored to compare the performance and current generation from microbial fuel cells containing motility-impaired mutants as well as wild type S. oneidensis. Furthermore, we studied and quantified the anodic biofilm morphological characteristics based on microscopic techniques. We found that type IV pili mutants exhibited the highest deficiencies in electrochemical performance and current production based on chronoamperometric studies. Specifically, these deficiencies were more pronounced on PilD and PilT protein-lacking mutants. These complexes are essential inner membrane proteins responsible for pili assembly and contraction [2]. On the other hand, flagella-lacking S. oneidensis mutants did not present significant restrains in current output and biofilm formation.

We conclude that the discussed structural protein assemblies present relevant roles in bacterial surface attachment. Our findings present direct implications in the development of fully engineered biohybrid assemblies, bacteria-anode interactions, and bacterial electron transfer quantification.

Figure 1. SEM images of wild type, pili-lacking and flagella-lacking mutants of S. oneidensis attached to carbon felt fibers.

  

References:

1. K.M. Thormann, R.M. Saville, S. Shukla, D.A. Pelletier, A.M. Spormann, Initial phases of biofilm formation in Shewanella oneidensis MR-1. J Bacteriol, 2004. 186: 8096–8104. 

2. R.M Saville, N. Dieckmann , A.M. Spormann, Spatiotemporal activity of the mshA gene system in Shewanella oneidensis MR-1 biofilms. FEMS Microbiol Lett. 2010. 308:76–83.