Macromolecular and structural evaluation of electricity-producing biofilms

ROBUSCHI L; SCHROTT GD; ORDOÑEZ MV; BONNANI PS; BUSALMEN JP

Mar del Plata

Congreso; VIII Reunión Anual de la SAMIGE; 2012

Sociedad Argentina de Microbiologia General

Geobacter sulfurreducens can use extracellular insoluble electron acceptors during anaerobic respiration. It can also use a polarized electrode for this function, thus producing an electric current. Elucidating mechanisms behind this mode of respiration is significant for the development of clean energy and wastewater treatment technologies, which are rapidly emerging. Controlling steps in current production are thought to be at the metabolic activity of cells, but still remain to be determined. In this work we profiled the content of macromolecules relevant for evaluating population physiology and growth during the development of G. sulfurreducens biofilms on polarized graphite electrodes. Confronting macromolecular data with current production reveled that the later is not related to DNA accumulation, but to the mean metabolic activity as indicated by the RNA:DNA ratio. Current:DNA and current:protein ratios on the other hand, showed that maximum respiratory rate is achieved after about 150 hours, during the exponential growth phase. At this time current output is at the maximum and latterly decreases to stabilize at about 4-6 A.m-2. Using phase contrast microscopy we also profiled growth-related parameters as biofilm thickness and 3D structure in situ and in vivo, using a customized flow cell with a transparent working electrode. Current output was observed to increase with biofilm thickness until about 40-50µm, to latterly become intriguingly independent of this parameter. Optical sectioning of biofilms evidenced cell clusters covering a maximum of 20-25% of the electrode area in the first 20-30 µm from the interface level. Beyond this limit biofilms structure was less dense with clusters protruding to the liquid phase. On the base of all collected evidences a model is proposed for the distribution of individual contributions from cells in different locations into the biofilm volume to the overall current production. Supported by European Commission (7th Framework Program, BacWire project)