Microbial Corrosion Prevention by Citrobacter sp. Biofilms

Microbiologically influenced corrosion (MIC) compromises the integrity of many technologically relevant metals. Protective coatings based on synthetic materials pose potential environmental impacts. Here, we report a MIC resistant coating based on a biofilm matrix of Citrobacter sp. strain MIC21 on underlying copper (Cu) surfaces. Three identical corrosion cells varying in the type of working electrode (annealed Cu, 29.5% coldworked, and 56.2% coldworked Cu) were used. Graphite plate and Ag/AgCl served as counter and reference electrodes, respectively. The working electrolyte was based on lactate-C media along with an inocula consisting of Oleidesulfovibrio alaskensis strain G20 and Citrobacter sp. strain MIC21. Passivating effect of the co-cultured biofilm matrix was observed in the form of an ennoblement effect. Tests based on sequencing, microscopy, and spectroscopy revealed the formation of a compact biofilm matrix dominated by strain MIC21 cells, exopolymers, and insoluble precipitates. This matrix displayed elastic modulus (a measure of rigidity) as high as 0.8 Gpa and increased corrosion resistance by ~10-fold. Interestingly, strain MIC21 has the capacity to inhibit the undesirable growth of aggressive strain G20. Additional corrosion tests also substantiated the passivation effects of strain MIC21. We provide mechanistic insight into the underlying reasons responsible for corrosion prevention behavior of the biofilm matrix.