AISI type 304 stainless steel (SS) specimens in solution annealed and cleaned and passivated conditions were exposed to laboratory culture of Leptothrix sp. Epifluorescence studies and total viable count analysis of these specimens showed that bacterial density and biofilm coverage were the least on cleaned and passivated SS surfaces. To confirm whether MnS inclusions play a role in this, adhesion studies at applied potentials, surface characterisation studies using SEM and EDAX analysis and pitting studies with ferric chloride were carried out. These studies clearly revealed the removal of MnS inclusions. This removal leads to a significant reduction in the adhesion of Leptothrix sp. The significance of the present study is that pretreatment of SS by cleaning and passivation inhibited the adhesion of Leptothrix sp. This reduction in adhesion is responsible for the increased corrosion resistance of SS under biofilms in aqueous environments.

A manganese oxidizing bacterium was isolated from the surface of steel scraps and biochemical tests and 16S rRNA sequencing analysis confirmed the isolate as Bacillus flexus. Potentiodynamic polarization curves showed ennoblement of open circuit potential, increased passive current, a lowering of breakdown potential, active re-passivation potential and enhanced cathodic current in the presence of B. flexus. Adhesion studies with B. flexus on SS304 specimens with different surface treatments demonstrated decreased adhesion on passivated and FeCl(3) treated specimens due to the removal of MnS inclusions. The present study provides evidence that surface treatment of stainless steels can reduce adhesion of this manganese oxidizing bacterium and decrease the probability of microbiologically influenced corrosion.