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, epifluorescence, and Tapping Mode(TM) atomic-force microscopy showed that the bacteria colonized some fraction of mineralogical aggregates. These aggregates were covered by bacteria and were linked together by relatively open biofilms consisting of networks of fiber-like attachment features intertwined through thin films of amorphous-looking organic material. The biofilm material encompassed numerous individual bacteria, as well as mineralogic particles. 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, branching fibrils intertwined through thin films. The detailed structures of these attachment features were highlighted by Phase Imaging atomic-force microscopy, which served as a real-time contrast enhancement technique and showed some poorly defined sensitivity to different surface materials, most probably related to differences in stiffness or viscoelasticity. Although the mechanism of the microbially enhanced dissolution remains unknown, we hypothesize that the bacteria may have produced micro environments conducive to dissolution through the we of observed extracellular materials.