Microincineration and elemental X-ray microanalysis of single Bacillus cereus T spores

Abstract

Single whole spores of bacillus cereus T were analyzed by scanning electron microscopy and electron microprobe X-ray microanalysis before and after high-temperature (600 °C) ashing in air. High-temperature ashing consisted of a centripetal oxidation of the spore surface combined with pyrolysis of the spore's interior. Ashing of single spores produced a compact central ash particle, mimicking the much larger unashed spore body in outline but containing craterlike microregions, and a peripheral thin ash film. Ashing mostly eliminated the spore's organic matrix; however, ash residues still gave residual carbon-characteristic X-ray counts. Ashing of single spores produced a two-, five-, and six-fold increase of potassium, magnesium, and calcium X-ray intensities, respectively. Iron, although low in actual counts, became detectable after ashing. Phosphorus characteristic X-rays were decreased by 41% after ashing, while volatilization lowered sodium and manganese X-ray intensities by over 80%. High-temperature ashing enhanced element-characteristic X-ray intensities of the non-volatilizable mineral(ized) elements of spores by compacting them into ash residues, more so than by simply abolishing their organic matrix. Microincineration appears a generally useful preconcentration technique for elemental detection and localization in X-ray microanalysis.