Colonization and biofilm formation of the extremely acidophilic archaeon Ferroplasma acidiphilum

• Ferroplasma acidiphilum biofilm formation was investigated.
• The presence of capsular polysaccharides was observed by CLSM using the fluorescent-labeled lectin Con A.
• Cells forming biofilms in floating filters were examined.
• AFM observations confirmed the ability of F. acidiphilum to form monolayer biofilms.

Ferroplasma spp. are widely distributed in acid mine drainage (AMD) and biomining environments at mesophilic and moderately elevated temperatures, at low pH and high concentrations of iron and other metal ions. Microbial attachment and biofilm formation on metal sulfides are of great importance during bioleaching. In this work, several cultivation and microscopical techniques were applied to investigate the biofilm development of Ferroplasma acidiphilum. Biofilms were heterogeneously distributed on filters over time, and varied within the different growth conditions such as supplementation with glucose. Additionally, cell distribution, biofilm formation as well as EPS production of F. acidiphilum cells forming biofilms on pyrite were observed by confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) combined with epifluorescence microscopy (EFM). Cells formed a monolayer biofilm and were preferably attached to the cracks/defects of pyrite surfaces. Biofilm and planktonic cells exhibited significant morphological differences. Capsular EPS were observed in both biofilm and planktonic cells.