Scanning Electron Microscopy


Electron microscope autoradiography and X-ray microanalysis have been used for the detection and quantitation of cations in the bacterium Pseudomonas tabaci. These techniques differ in the information they provide (relating to either cation uptake or in situ levels), their applicability to different cations, their sensitivity and their spatial resolution. With uptake of 63Ni2+, high resolution autoradiography (involving gold latensification and physical development) demonstrated a high degree of cation localisation to the central nucleoid area (glutaraldehyde-fixed cells) and within this to the constituent chromatin (acetic-alcohol preparations).

X-ray microanalysis of whole bacterial cells revealed the presence of substantial levels of K (mainly soluble cation}, Ca, Mn, Ni, Cu and Zn (mainly in soluble cations) and Fe (present as major soluble and insoluble components). The use of whole cells provided a particularly useful experimental system to demonstrate the importance of cell preparation technique in relation to element detectability. The application of X-ray microanalysis to lysed cells permitted analysis of extruded contents -including cell protoplast (protoplasm without associated cell wall material) and chromatin fibrils. The microprobe detection of DNA-associated cations was most effective with freshly extracted chromatin and showed the presence of bound K, Ca and transition metals.

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