Reversible Acceleration of the Corrosion of AISI 304 Stainless Steel Exposed to Seawater Induced by Growth and Secretions of the Marine Bacterium <i>Vibrio Natriegens</i>

Abstract

Growth of the nonsulfate-reducing marine bacterium Vibrio natriegens increased the corrosion current density (CD) of AISI 304 stainless steel (SS) coupons when grown in a marine medium. The corrosion rate, estimated as the corrosion CD (Icorr), calculated from the Tafel constants and polarization resistance, increased from 230 to 2900 nA/cm2 during a 6-day incubation period with V. natriegens. Just before the rapid increase in the corrosion CD, bacterial cells were seen by epifluorescent microscopy after acridine orange staining to colonize the SS surface. On the third day of exposure to seawater, the rapid increase in the corrosion CD correlated with the appearance of extracellular material from the colonizing bacteria, as observed by (1) epifluorescent microscopy, (2) scanning electron microscopy (SEM), and (3) nondestructive analysis of lyophilized biofilms by Fourier transform-infrared spectroscopy (FT-IR) using diffuse reflectance. The extracellular products from the colonizing bacteria correlated with the rapid increase in infrared absorbance at ~ 1440 cm−1. The IR spectrum of the ~ 1440 cm−1 component corresponds to authentic calcium hydroxide possibly associated with an organic matrix. Bacterial colonization reached the maximum extent on the fourth day, as monitored by the infrared absorption at ~ 1660 cm−1, which corresponds to the amide I vibrations in the bacterial proteins as well as in the appearance of the biofilm in epifluorescent microscopy. The increase in the corrosion CD continued after the decrease in the rate of bacterial colonization. Removing the biofilm with sonication and washing decreased the bacterial content of the biofilm monitored at ~ 1660 cm−1 to a greater extent than the extracellular calcium hydroxide monitored at ~ 1440 cm−1. This had essentially no effect on the corrosion CD. Sonication followed by extraction with chloroform-methanol removed the extracellular exudation and the bacteria with a 10-fold decrease in the CD. A related bacterium, V. anguillarum, showed a smaller increase in corrosion CD that correlated with a smaller increase in infrared absorbance at ~ 1440 and ~ 1660 cm−1. The present study shows the reversible facilitation of the corrosion of SS exposed to seawater by organisms and extracellular accumulations of nonsulfate-reducing marine bacteria.