Figure shows the formation of thick and uniform EPS in which the rod-shaped bacteria were well distributed. This biofilm was produced by the biological activity and proliferation of the PA-ZK bacteria on the surface of SS304 during 14 days of incubation. Due to the biological activities of the bacteria in the dense biofilm, in the produced EPS layer, the dissolved oxygen within this biofilm is consumed and introduced a concentration gradient as shown in Figure . The depletion of the dissolved oxygen at the biofilm/substrate interface could result in surface polarization and limited the corrosion reactions controlled by the supply of oxygen at the SS304 surface. In the presence of dense and uniform PA-ZK containing biofilm, the dissolved oxygen was consumed by the biological activities of the bacteria and SS304 and limited current in cathodic polarization curve of S2 system (Figure ) was attributed to the depletion of oxygen. However, the biofilm produced by BS-S1X bacteria contained pores and the SS304 surface was locally exposed to the ionic species in the S3 medium. The localized dissolution of the SS304 was associated with the formation of differential aeration cells within the porous EPS containing biofilm. These effects were evident after the removal of biofilm, where the topographical analysis revealed localized corrosion of the SS304 samples in both S1 and S3 media. Due to the dissolution of the metal ions at the local anodic sites, the EPS layer is modified and facilitates electron tunnelling, which may result in an increased corrosion rate due to the depolarization of the cathodic regions. The origin of reflectance peaks in the FTIR spectra within 400 and 900 cm -1 confirmed the stretching vibrations of the Fe, Cr and Ni oxides in the EPS layer. Similarly, the peaks signatures between (900 -1400 cm -1 ), 1550 and at 1650 cm -1 ) corresponded to the ether (C-O-C), amide I and amide II functional groups, which represent the presence of polysaccharide and protein molecules on the surface of SS304 samples. The peak between 3400 to 3900 cm -1 (NH/OH) were attributed to the hydroxyl group of the adsorbed water and amino group (NH) of proteins in the EPS .