The relationship between alloying elements and biologically produced ennoblement in natural waters

Cathodic polarization enables SEM illustration of manganese biomineralization in natural biofilms

Manganese biomineralization occurred readily on metal surfaces in a natural freshwater environment. SEM demonstration of actual bacterial participation was challenging due to the rapidity of biofilm growth and typical microbe-mineral agglomeration. By optimizing cathodic polarization, we slowed down the process so effectually as to document biomineralization by rod-shaped rather than by filamentous bacteria which occurred more frequently at open circuit.

Portraying manganese biofilms via a merger of EPR spectroscopy and cathodic polarization

Microbial biofilms on stainless steel surfaces exposed to water from a freshwater pond were dominated by manganese-oxidizing bacteria, as initially diagnosed by microscopy and elemental analysis. The application of electron paramagnetic resonance (EPR) spectroscopy revealed conspicuous sextet (six-line) patterns that intensified with immersion time, implying the gradual accumulation of Mn(II) in the biofilms. Correspondingly, cathodic polarization designated the manganese oxide (MnO_x) reduction peak in the form of a distinctive 'nose', which grew increasingly more negative with biofilm growth. The progressive expansion of cathodic current densities and the concurrent area-under-the-curve also allowed the quantification of microbially mediated MnO_x deposition_. Furthermore, the merger of EPR and cathodic polarization techniques yielded key insights, in tandem with Mn speciation data, into the pathways of microbial manganese transformations in biofilms, besides providing meaningful interpretations of prevailing literature. Accordingly, the natural freshwater biofilm was inferred as one supporting a complete manganese cycle encompassing multiple redox states.