Sudden Emergence of Redox Active Escherichia Coli Phenotype: Cyclic Voltammetric Evidence of the Overlapping Pathways

Under anaerobic and static culture condition, Escherichia coli K-12 (E. coli) biofilm was adapting electrochemically on gold electrode in well-defined redox environments modulated by a computerized potentiostat. The electrochemical property of the biofilm/electrode interface was investigated during the 168 h of biofilm adaptation. In-situ cyclic voltammogram (CV) revealed a sudden transition into redox active phenotype after 24 h incubation at 0 V and 0.2 V, which seems to be controlled by quorum-sensing mechanism. Further analysis of CV results implies the kinetic details of extracellular respiration. The simultaneous linear dependence of the peak current on the scan rate and the square root of the scan rate suggest the coexistence of surface and diffusion controlled process which was likely due to the overlapping pathways of direct and indirect electron transport. It is for the first time that the mixed controlled regime has been observed at cellular level. To gain further insight in to the redox active adaptation, cellular redox state was monitored through out the course. Although in the natural condition where the redox environment was not artificially controlled E. coli adapted towards lower cellular redox state that thermodynamically favored the electron transport, it did not evolve to redox active phenotype. Similar trends of adaptation of cellular redox state towards lower potential were observed in the 0 V and 0.2 V redox environments. Moreover, differentiated early stage response in cellular redox state suggests parallel adaptation processes which were eventually dominated by extracellular respiratory activity as indicated by the convergence of the mixed cellular potential to the redox midpoint potential in the later stages of adaptation