Center for Biofilm Engineering (CBE)

Now showing 1 - 3 of 3

Biocorrosion
(2000) Geesey, Gill G.; Beech, Iwona; Bremer, Philip J.; Webster, Barbara J.; Wells, D. Bret
Resolving biogeochemical phenomena at high spatial resolution through electron microscopy
(2008-06) Geesey, Gill G.; Borch, Thomas; Reardon, Catherine L.
Our understanding of microbe-metal interactions has advanced dramatically since the mid-1970s when little was known about the reactivity of bacterial cell wall components toward metal ions in the extracellular milieu. Although certain metals such as and Pb+ were known to react with components of bacterial cell walls and used to visualize their structure by electron microscopy (Garland et al., 1975), little physicochemical data were available on the specificity and sites of interactions (Humphrey & Vincent, 1966; Heptinstall et al., 1970; Irvin et al., 1975; Lambert et al., 1975; Raymond & MacLeod, 1975). Furthermore, there were no model systems to explorethe mechanisms of these interactions. This began to change when Beveridge and Murray used isolated cell walls of Bacillus subtilis to quantify metal ion binding to wall components. Beveridge demonstrated that cell walls concentrated cations such as Mg++, Na+, K+, Cu++ and Fe+++, but not Ba++, Li+ or Al+++ (Beveridge & Murray, 1976). Since these initial studies, Beveridge and his students and collaborators have contributed greatly to our understanding of the complex interactions between microbial cell surface polymers and metals in the environment. As fellow scientists working in this research area, we have developed a deep admiration of Beveridge’s scientific insight, technical skills and collegial demeanor. Not surprisingly, Beveridge’s research has had a significant impact on our research, as well as on the research of our collaborators and colleagues, and will likely influence the work of future generations of scientists working in the field of geobiology. Some examples are cited below.
Role of outer membrane c-type cytochromes MtrC and OmcA in Shewanella oneidensis MR-1 cell production, accumulation, and detachment during respiration on hematite
(2012-07) Mitchell, Isaac; Peterson, L.; Reardon, Catherine L.; Reed, S. B.; Culley, D. E.; Romine, Margaret F.; Geesey, Gill G.
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 Î”omcA mutant but not those of a Î”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 themineral surface from cell respiration associated with achievement of high surface cell densities.

Center for Biofilm Engineering (CBE)

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