Sulfate reducing activity and corrosion potential of diverse heterotrophic facultative bacteria isolated from crude oil pipeline residues

Sulfate-reducing bacteria are vital in biogeochemical cycles and can significantly affect both environmental and industrial processes, including biocorrosion. This study investigates the sulfate-reducing potential of various heterotrophic facultative bacteria isolated from crude oil samples collected at various points in a petroleum refinery, after a crude oil pipeline pigging operation. The samples were analysed to identify the microbial communities and their metabolic capabilities. Bacterial strains of Enterobacter cloacae, Enterobacter ludwigii, Enterobacter hormaechei, Citrobacter braakii, Citrobacter freundii and Pantoea hericii were isolated from the crude oil samples using selective enrichment. Their sulfate reducing potential was assessed by measuring sulfide production and growth under various environmental conditions. Significant variability in sulfate-reducing activity among the isolated strains, with some exhibiting notably high reduction rates. Molecular identification via 16S rRNA sequencing was employed to characterize the strains and elucidate their phylogenetic relationships. Furthermore, corrosion capacity of the most promising bacterial strain among those identified, E. cloacae on API 5L X65 pipeline material was analysed using the potentiodynamic polarization method. Under abiotic conditions, the corrosion rate was measured at 0.09 mm per year, with a corrosion current density of 1.69 × 10⁻⁵ A cm⁻². However, in the presence of facultative bacterium E. cloacae, the corrosion rate increased significantly to 0.23 mm per year, accompanied by corresponding I_corr value of 3.29 × 10⁻⁵ A cm⁻². This study contributes to a better understanding of the ecological roles of facultative sulfate reducing bacteria in industrial environments, especially within crude oil processing.