In situ generated antimicrobials in genetically-engineered biofilms to inhibit corrosion of steel

In this study, corrosion inhibition of SAE 1018 mild steel with axenic Pseudomonas fragi K and Escherichia coli biofilms has been studied in quiescent batch cultures and a two to ten-fold inhibition has been observed. To determine if corrosion inhibition is a general property of all bacteria, aerobic bacteria belonging to seven different genera were evaluated for their ability to inhibit corrosion of SAE 1018 mild steel in axenic cultures. The observed corrosion inhibition of each bacterium depended on the degree of biofilm formation in the growth medium used; Streptomyces lividans TK24 did not form a biofilm in rich LB medium and corroded similar to sterile controls, whereas it grew to moderate turbidity in the minimal VNSS medium and protected metal the most.; The role of oxygen depletion in corrosion inhibition of SAE 1018 steel by axenic aerobic biofilms has been delineated using electrochemical impedance spectroscopy (EIS) which provides a better understanding of the corrosion process taking place at the metal surface. It has been shown that an axenic aerobic biofilm can inhibit corrosion of SAE 1018 mild steel by 40-fold in continuous reactors.; Desulfovibrio vulgaris, a sulfate-reducing, anaerobic bacterium that has been reported to be able to withstand oxygen stress and implicated in accelerating corrosion of mild steel was used as a reference sulfate-reducing bacteria (SRB). This strain was combined with various aerobes to obtain corrosion rates with SAE 1018 mild steel and 304 stainless steel. Attempts to kill SRB with ampicillin, chloramphenicol, anthraquinone, and sodium molybdate after they had colonized the aerobic biofilm proved to be unsuccessful; no decrease in corrosion was observed. However, when SRB-inhibitory antimicrobials were present in the biofilm prior to SRB addition (by adding purified chemicals), growth of SRB on stainless steel was completely inhibited. A gramicidin S-producing bacterium (Bacillus brevis 18) was also able to form a protective biofilm against SRB and inhibit corrosion of 304 stainless steel, as was verified by the external addition of the purified antimicrobial gramicidin S to a non-antimicrobial producing Pseudomonas fragi K biofilm. The purified peptide antimicrobials indolicidin and bactenecin from bovine neutrophils, polymyxin B from the bacterium Bacillus polymyxa, and gramicidin S from the bacterium Bacillus brevis 18 have been shown to inhibit the growth of Desulfovibrio vulgaris and Desulfovibrio gigas in suspension cultures by 90%.; Since they were effective in killing SRB, indolicidin and bactenecin were synthesized as complementary oligonucleotides and cloned into the Escherichia coli-Bacillus shuttle vector pBE92 under the control of the constitutive alkaline protease (apr) promoter.; These constructs have been transformed into Bacillus subtilis BE1500, Bacillus subtilis WB600 (a protease-deficient strain of Bacillus), and Bacillus polymyxa (which produces polymyxin) and their ability to inhibit the growth of SRB on 304 stainless steel determined. (Abstract shortened by UMI.)...