Attachment of a Pseudomonas sp. to Fe(III)-(hydr)oxide surfaces

As a first step towards understanding microbial dissolution processes, our research focuses on characterizing attachment features that form between a Pseudomonas sp. bacteria and the Fe(III)-(hydr)oxide minerals hematite and goethite. Microbial growth curves in Fe-limited growth media indicated that the bacteria were able to obtain Fe from the Fe(lll)-(hydr)oxides for use in metabolic processes. A combination of scanning electron microscopy, epif luorescence, and Tapping Mode(TM) atomic-force microscopy showed that the b acteria colonized some fraction of mineralogical aggregates. These aggregat es were covered by bacteria and were linked together by relatively open bio films consisting of networks of fiber-like attachment features intertwined through thin films of amorphous-looking organic material. The biofilm mater ial encompassed numerous individual bacteria, as well as mineralogic partic les. We hypothesize that the bacteria first attached to mineral aggregates, perhaps via their flagella, forming colonies. Following initial attachment , the bacteria exuded additional attachment features in the form of fine, b ranching fibrils intertwined through thin films. The detailed structures of these attachment features were highlighted by Phase Imaging atomic-force m icroscopy, which served as a real-time contrast enhancement technique and s howed some poorly defined sensitivity to different surface materials, most probably related to differences in stiffness or viscoelasticity. Although t he mechanism of the microbially enhanced dissolution remains unknown, we hy pothesize that the bacteria may have produced micro environments conducive to dissolution through the we of observed extracellular materials.