From Twitching to Nanowires Toward a Holistic Understanding of Motility Structures and Extracellular Electron Transfer in Shewanella Oneidensis

Extracellular electron transfer (EET) in dissimilatory metal reducing bacteria, such as Shewanella oneidensis and Geobacter spp., is thought to be mediated by nanowires composed of type IV pili encased in membrane-bound cytochromes. ^1,2   Type IV pili are also required for EET competent biofilm formation in these organisms. ³ Although the necessity for the involvement of T4P in biofilm formation has been established, surface motility has not been observed in these organisms, ^3,4 whereas it is required in other g-proteobacteria.   ⁵

Using self-assembled monolayers (SAMs) of ω-substituted alkanethiolates on gold, we have recently demonstrated that twitching motility occurs in Shewanella oneidensis MR1 and that it is responsive to the chemistry of the substratum.  In addition, using deletion mutants, we are eludicating the roles of the two classes of T4P present (PilA and Msh) in S. oneidensis in surface motility and their significance in biofilm formation. (Figure 1) We have found that while both types of pili are required for wild-type early biofilm formation, either pilus on its own is sufficient for twitching surface motility.  We are also exploring the formation of nanowires and subsequent EET for this set of mutants. 

In this presentation, we discuss the known and possible interrelationships between surface motility, nanowire production, biofilm formation and EET, including mechanisms for their molecular coordination.    We predict that manipulation of engineerable parameters can modulate these cellular activities for better design of microbial biofuel cells.     

References

(1) El-Naggar, M. Y.; Finkel, S. E. Scientist 2013, 27, 38.

(2) Lovley, D. R. Energy & Environmental Science 2011, 4, 4896.

(3) Saville, R. M.; Dieckmann, N.; Spormann, A. M. FEMS Microbiol Lett 2010, 308, 76.

(4)Thormann, K. M.; Saville, R. M.; Shukla, S.; Pelletier, D. A.; Spormann, A. M. J Bacteriol 2004, 186, 8096.

(5)O'Toole, G. A.; Kolter, R. Mol Microbiol 1998, 30, 295.

Acknowledgements

This work was supported through ARO grant W911NF-12-1-0208.