A build-up of any biomass (bacterial biofilm for instance) on a machine part etc. will certainly impede the function of said part. Biofilms inside pipes will slow flow rates, for example. Personally, I don’t know if the bacteria actually damage the surface or coating, it’s certainly possible. Try searching for ‘bio fouling’. I think that some organisms may use a metal surface as an electron acceptor for respiration (Shewanella on uranium…?); this suggests that indeed metal surfaces can be ‘altered’ (damaged) directly by bacterial biofilms.

Dear Mark Reuter

Thanks for your reply. So far I understood that biofilm/ biofouling formation on coatings (on metal structures) reduce the insulative behaviour of the coatings.  I too agree that these organisms interact directly wit the metal/alloys. But I do not know how they participate in lowering the protective performance of the coating on a metal surface.