CHARACTERIZATION OF AXENIC PSEUDOMONAS-FRAGI AND ESCHERICHIA-COLI BIOFILMS THAT INHIBIT CORROSION OF SAE-1018 STEEL

Corrosion inhibition of SAE 1018 steel by Pseudomonas fragi and Escher ichia coli biofilms has been evaluated using batch cultures in rich me dium (LB) and seawater-mimicking medium (VNSS) at 23 degrees C and 30 degrees C with or without daily medium replenishment. Biofilm componen ts have been stained simultaneously for polysaccharide (calcofluor) an d live and dead cells (Live/Dead Baclit viability I;it) and visualized using confocal scanning laser microscopy (CSLM). Image analysis was u sed to quantify the relative proportions of live cells, dead cells, po lysaccharide and void space in the biofilm. This staining technique an d examination of the architecture of biofilms responsible for inhibiti ng metal corrosion revealed that both Ps. fragi and E. roll produce po lysaccharide only in the seawater medium; in rich medium, the biofilm consisted mainly of a layer of sessile cells near the biofilm-metal in terface and sparse thick clumps of cells at the biofilm-liquid interfa ce. Biofilms of both strains had a higher proportion of live cells in the rich medium than in the seawater-mimicking medium at the higher te mperature, and more live cells were present at the higher temperature for LB medium. The corrosion inhibition observed (2.3-6.9-fold in 8 d) was not significantly affected by medium type or replenishment. Incre ase in the cellular content of the biofilms, as a result of increasing temperature, led to a reduction in corrosion.