IMAGING A PSEUDOMONAD IN MINERAL SUSPENSIONS WITH SCANNING FORCE AND ELECTRON-MICROSCOPY

Techniques for imaging bacteria in their physical environments yield i nformation potentially relevant to better understanding the role of so il and sediment colloids in altering microbial activity. Although cell structure and morphology of bacteria have been previously investigate d using light and electron microscopies, both approaches are not witho ut deficiencies. Our objective was to demonstrate the utility of scann ing force microscopy (SFM) to image cell morphologies and to observe i nteractions between bacteria and clay minerals. Pseudomonas fluorescen s (Migula), strain 2-79 RN(10), was imaged in pure culture and in susp ensions of kaolinite and montmorillonite using both SFM and, for compa rison purposes, SEM (scanning electron microscopy). Large-scale SFM an d SEM images were similar, thus confirming the lack of artifacts intro duced by SFM. Images of bacteria in kaolinite suspensions were not obt ained with either technique, a result attributed to bacterial isolatio n in large pores of the kaolinite matrix. Imaging of montmorillonite-b acteria suspensions showed that bacteria were closely associated with the larger mineral particles. In addition, the high resolution of SFM revealed what appeared to be small hexagonal montmorillonite platelets adhering to cell surfaces. The features of SFM allow for this unique ability to image whole cells as well as the microtopography of cell su rfaces within hydrated environments. Scanning force microscopy provide s valuable information concerning microbial cell morphology and the in teraction of bacterial cells with montmorillonite.