|Mitchell, Andy -|
|Peterson, Luke -|
|Reed, S -|
|Culley, D -|
|Romine, M -|
|Geesey, Gill -|
Submitted to: Geobiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 19, 2012
Publication Date: February 23, 2012
Citation: Mitchell, A.C., Peterson, L., Reardon, C.L., Reed, S.B., Culley, D.E., Romine, M.F., Geesey, G.G. 2012. Role of outer membrane c-type cytochromes MtrC and OmcA in Shewanella oneidensis MR-1 cell production, accumulation and detachment during respiration on hematite. Geobiology. 10, 355-370. Interpretive Summary: Shewanella oneidensis MR-1 is a model bacterium for study of microbial metal reduction. S. oneidensis MR-1 is able to respire crystalline iron oxides such as hematite using the outer membrane cytochromes OmcA and MtrC for electron transfer to the mineral. In this study, we investigated how the cytochromes affect biofilm formation on hematite when using the mineral for respiration. MtrC but not OmcA is required for growth on the mineral surface however OmcA was required for efficient electron transfer once the biofilm had developed. These results indicate that the two cytochromes have different roles in the respiration of hematite.
Technical Abstract: The iron-reducing bacterium Shewanella oneidensis MR-1 has the capacity to contribute to iron cycling over the long term by respiring on crystalline iron oxides such as hematite when poorly crystalline phases are depleted. The ability of outer membrane cytochromes OmcA and MtrC of MR-1 to bind to and transfer electrons to hematite has led to the suggestion that they function as terminal reductases when this mineral is used as a respiratory substrate. Differences in their redox behavior and hematite-binding properties, however, indicate that they play different roles in the electron transfer reaction. Here, we investigated how these differences in cytochrome behavior with respect to hematite affected biofilm development when the mineral served as terminal electron acceptor (TEA). Upon attachment to hematite, cells of the wild-type (WT) strain as well as those of a 'omcA mutant but not those of a 'mtrC mutant replicated and accumulated on the mineral surface. The results indicate that MtrC but not OmcA is required for growth when this mineral serves as TEA. While an OmcA deficiency did not impede cell replication and accumulation on hematite prior to achievement of a maximum surface cell density comparable to that established by WT cells, OmcA was required for efficient electron transfer and cell attachment to hematite once maximum surface cell density was achieved. OmcA may therefore play a role in overcoming barriers to electron transfer and cell attachment to hematite imposed by reductive dissolution of the mineral surface from cell respiration associated with achievement of high surface cell densities.