This paper reports the microbiologically induced corrosion (MIC) and electrochemical behavior of carbon steel (API 5LX) in the presence of hydrocarbon-degrading bacteria Bacillus cereus ACE4 (a Gram-positive bacterium) and Serratia marcescens ACE2 (a Gram-negative bacterium). Weight loss studies and metallographic analysis of the metal API 5LX exposed to a simulated corrosive environment showed that the bacterium ACE4 caused severe pitting corrosion than that of bacterium ACE2. As part of biodegradation studies, the impact of aryl hydrocarbon hydroxylase (AHH) on diesel degradation was investigated along with reduction of total hydrocarbons. It was clearly observed that, during the biodegradation experiment in the presence of B. cereus ACE4, the content of the total hydrocarbons decreased significantly due to their metabolism induced by AHH enzymes when compared to S. marcescens ACE2. Degraded petroleum hydrocarbons (diesel) act as a good nutrient for bacteria, which in turn increases the proliferation of bacteria on the steel and determines the nature of corrosion. Metal oxides such as MnO2 and Fe2O3 were found as part of the corrosion products, indicating that the ACE4 bacterium is capable of converting the elements on the carbon steel (API 5LX) to their metal oxides and thus accelerating severe pitting corrosion on the surface of the pipeline networks. Overall, the study provides an insight into the microbiologically influenced corrosion of carbon steel API 5LX by two hydrocarbon-degrading bacteria in diesel fuel/water mixtures.