An investigation of microbiologically induced corrosion was carried out on AISI 1006 carbon steel using Acidithiobacillus ferroxidans and Citrobacter murliniae. This study was aimed to compare the resultant corrosion by the two bacteria for 7 and 21 days, either in the presence or in the absence of Bacillus subtilis as a metal corrosion inhibitor. According to the weight-loss experiment, there was no significant difference in weight loss (within the range of 4–5%). However, SEM results showed contrast corrosion surfaces occurring, uniform and pitting corrosion for those bacteria. Major damages were observed during a longer period of immersion to bacterial cultures.