Mn cycling in marine biofilms: effect on the rate of localized corrosion

Microelectrodes of the Au-Hg amalgam type have been used together with square wave voltammetry to measure profiles of oxygen, peroxide, Fe, Mn and sulfur chemical species through the thickness of natural assemblage marine biofilms grown on stainless steel alloy Nitronic 50 (UNS S20910). The data show Mn+2 and peroxide together at locations where the dissolved oxygen concentration was low. Oxidized species of Fe were also found at some locations. Sulfur species (predominantly S-2) was often found at locations where the dissolved oxygen concentration was below the detectable limit. Confocal scanning laser microscopy was used to image the microbial assemblage at the locations of the chemical profile data. Organisms with a filamentous morphology were found in consortia with rod and coccoidal shaped microbes at locations where dissolved Mn and peroxide were measured. The filamentous forms were usually absent at locations where Mn was not detected. It is suggested that the filamentous organisms may be Mn metabolizers, and that peroxidatic Mn re-oxidation may be taking place within the biofilm.