Synergistic action of Bacillus subtilis, Escherichia coli and Shewanella putrefaciens along with Pseudomonas putida on inhibiting mild steel against oxygen corrosion.

Microbial biofilm can effectively alter the electrochemical characteristics at metal/solution interface that can either accelerate or decelerate corrosion. The present paper reports about microbiologically induced corrosion inhibition (MICI) using Pseudomonas putida as a dominant bacterium under aerobic condition. Effective corrosion inhibition is achieved by the synergistic metabolic action of P. putida along with Escherichia coli, Bacillus subtilis or Shewanella putrefaciens. The synergistic metabolic actions of these bacteria in biopassivation are analysed with various aspects such as electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM) and confocal laser scanning microscopy (CLSM). Surface topography is quantitatively analysed using optical scanning profilometry (OSP). The binary culture system containing P. putida + E. coli and P. putida + S. putrefaciens achieves an inhibition efficiency of 90% and 85% respectively, despite S. putrefaciens being a corrosion causing bacteria. The P. putida + E. coli system could form a stable biofilm on mild steel surface, with a high corrosion potential (- 329 mV vs. Ag/AgCl/KCl sat'd) and a low corrosion rate (1.65 × 10 mmpy). The presence of B. subtilis in the culture promotes corrosion against normal predictions. In the present case, the metabolic activities of the bacterial system on the mild steel surface cause depletion of oxygen in the medium that leads to suppression of corrosion. In addition, the biofilm could form an effective protective barrier on the metal surface that can suppress diffusion of corrosion products resulting in enhanced corrosion inhibition efficiency.