K-080. Metabolic Dynamics and Heterogeneity in Shewanella oneidensis Biofilms

T. K. Teal1, I. Ramos2, B. J. Wold1, D. K. Newman2;
1California Inst. of Technology, Pasadena, CA, 2Massachusetts Inst. of Technology, Cambridge, MA.

Bacteria in biofilm communities are resilient to changes in environmental conditions and resistant to toxins and antibiotics. The communities are spatially stratified and metabolically heterogeneous, suggesting that cells within them may respond differentially to environmental changes. Some regions within the community are not growth-active, but are still capable of generating energy for maintenance. To determine whether these growth-inactive regions are able to dynamically respond to nutrient changes and how growth-activity profiles might be affected by these changes, we modified the nutrient environments of mature Shewanella oneidensis biofilms and monitored growth activity. We first determined that growth activity, as measured by fluorescence from a GFP ribosomal reporter construct, could be affected by changes in nutrient concentrations, showing that fluorescence increased when fumarate was added to planktonic cultures at different concentrations. Growth activity in developing Shewanella oneidensis biofilms was then tracked in vivo, using confocal microscopy to image the spatial localization of fluorescence. Using quantitative image analysis, we determined regions of growth activity and how these profiles changed when nutrient conditions were changed. We found that cells previously growth-inactive could become active with the addition of the electron acceptor, fumarate. We developed a reaction-diffusion model for fumarate and oxygen distribution in biofilms and determined that profiles of growth activity are consistent with electron acceptor availability. Additionally, if we added AQDS, which can act as electron shuttle, growth activity within the biofilm was affected. In contrast, the addition of an electron donor, lactate, had little effect on biofilm metabolic profiles. These findings suggest that metabolic organization of S. oneidensis biofilms is dynamic and influenced primarily by the availability of an electron acceptor.