Microbial Corrosion of Aluminum 2024 Aeronautical Alloy by Hydrocarbon Degrading Bacteria Bacillus cereus ACE4 and Serratia marcescens ACE2

Microbial growth and contamination in aviation fuel storage tanks and aircraft wing tanks cause metal corrosion, plugging of the fuel filter, and increased maintenance costs associated with these problems. This paper reports the microbiologically induced corrosion (MIC) and electrochemical behavior of aluminum alloy (AA 2024) in the presence of hydrocarbon-degrading bacteria Bacillus cereus ACE4 (a Gram-positive bacteria) and Serratia marcescens ACE2 (a Gram-negative bacteria). Electrochemical impedance spectroscopy and metallographic analysis of the metal AA 2024 exposed to a simulated fuel tank environment showed that the bacteria caused pitting corrosion. Scanning electron microscopy energy-dispersive X-ray spectroscopy analysis (SEM-EDAX), atomic force microscopy (AFM), and Fourier-transform infrared spectroscopy (FTIR) analyses of the aluminum alloy coupons with bacterial biofilm developed after exposure to minimal salt medium confirmed that extracellular polymeric substances accumulate with exposure time and revealed that biofilms are formed as microcolonies, which subsequently cause pitting corrosion. Hydrophobicity of the cell surface was examined using bacterial adhesion to hydrocarbons (BATH) assay. The hydrophobicity and emulsification index of B. cereus ACE4 grown in n-hexadecane containing medium was higher (86% and E-72 85%) than that of S. marcescens ACE2 (60% and E-72 75%), This significant difference may be due to the efficiency of biosurfactant production, which contributes to increase in the cell surface hydrophobicity of the B. cereus ACE4, and enhanced bacterial adhesion on the AA 2024 metal surface. The corrosion damage caused by B. cereus ACE4 is vigorous compared with that from S. marcescens ACE2. This study provides some insight into the MIC of AA 2024 by two hydrocarbon-degrading bacteria in fuel/water mixtures.