Molecular Characterization of Microbial Communities Associated with Accelerated Low-water Corrosion (ALWC) on European Harbour Structures

The microbial communities associated with different corrosion deposit layers retrieved from a harbour steel structure affected by ALWC (Accelerated Low Water Corrosion) were determined by 16S rDNA PCR-DGGE analysis. Comparative analysis of populations associated with ALWC layers and NLWC (Normal Low Water Corrosion) layers evidenced clear differences in the structure and composition of the communities. Dominant phylotypes related to sulphate-reducing bacteria pertaining to Desulfobacteraceae, Desulfobulbaceae and Desulfovibrionaceae were identified in both type of deposits (fraction of 52% and 44% of the total NLWC and ALWC communities, respectively). Phylotypes related to sulphur-oxidizing bacteria belonging to Alpha-, Gamma- and Epsilonproteobacteria were unique to ALWC deposits, while phylotypes related to oxygenic photosynthetic microorganisms (cyanobacteria, diatoms) were only retrieved in NLWC deposits. This suggested that biologically-mediated sulphur cycle was the dominant process within ALWC deposits vs. chemically-mediated sulphur cycle within NLWC deposits. Since most of the members identified are heterotrophs, it is speculated that organic carbon may be available through water pollution and/or proliferation of photosynthetic biomass. Differences in oxygen concentration between ALWC and NLWC areas due to photosynthetic activities in NLWC may be an important factor contributing to the acceleration of corrosion by the mechanism of differential aeration.