Herein reported laboratory investigation was undertaken to determine whether unexpected field failures of 70/30 Cu-Ni alloy operating in a marine environment were due to biofilm-influenced corrosion. Fouling layers comprising biofilms and corrosion products were collected from surfaces of Cu-Ni alloys from two different systems were pitting corrosion was reported （systems coded T1 and T2）， from a non-corroding system coded V and from a newly commissioned （2 months old） system coded A, all at different geographic locations in the UK. An average temperature of seawater in T1,2 and A and in V systems was 24oC for the former systems and 10oC for the V system. Aerobic and anoxic enrichments were prepared by inoculating fouling material into media selective for slime- and acid-producing and sulfide-generating, including sulphate-reducing,prokaryotes. Following incubation at appropriate temperatures, enrichments representing each system were combined and used as inocula for the seeding of continuous flow bioreactors operating for 6 months with filter-sterilized natural seawater at two different temperatures （10oC and 24oC for systems T1 and V and 24oC only for systems T2）。 Bioreactor representing system A was run for 2 months at 24oC. Microscopy, surface spectroscopy and molecular ecology analysis were undertaken to characterize biofilms on and corrosion damage of specimens exposed in bioreactors and corresponding sterile controls. Varying degree of pitting attack and distinct pitting morphologies were seen on surfaces of specimens following biofilm removal. Localized attack mirroring field failures was observed on specimens exposed in the V-24 oC and T1-, T2- and, to some extent, A-24 oC bioreactors. Micropits detected on Cu-Ni surfaces in V- 10oC and in control reactors did not exceed depths typically reported for 70/30 Cu-Ni alloys in marine environments. Characterization of inocula and resulting biofilms through 454 pyrosequencing and DNA microarray analysis （GeoChip4R）， revealed similarities between composition of enriched microbial communities obtained from V, A and T1,2 systems. A high abundance of Cu-resistant genes was detected in biofilm populations, irrespective of their origins. The frequency of genes representing S-redox pathways and methanogenesis was considerable. However, the observed pitting was not due to the production of sulfide, but most likely due to slime and acid accumulation. Indeed, the prevailing taxon in bioreactor biofilms was that of facultatively aerobic iron oxidising, nitrate reducing Marinobacter spp. Although dominant in bioreactor inocula, 16S rRNA sequences representing sulfide producing organisms of the class Clostridia were not prominent in biofilms. The newly commissioned, system A already accumulated biofilm population, which, while scarce, was similar in structure to that of severely corroding systems T1,2. The study revealed that biofilms were responsible for the pitting attack on 70/30 Cu;Ni and that in the investigated systems, material and not geographic locations was likely to play a key role in influencing the structure and/or metabolic profile of complex biofilm community.

 

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