Dynamic SIMS ion microscopy imaging of individual bacterial cells for studies of isotopically labeled molecules

A CAMECA IMS-3f SIMS ion microscope instrument capable of 500 nm spatial resolution was used for imaging single bacterial cells in the soil treated with 13C-labeled phenol in desired treatments. After formaldehyde fixation, the soil samples containing bacterial cells were smeared on the silicon substrate. The O2+ primary ion beam was used for the detection of negative secondary ions. Images of individual bacterial cells were recorded on a CCD camera in masses 24, 25, 26, and 27 signals. The respective mass images represented contributions from the molecular ions of interest, for example 24(12C2)−, 25(13C12C)−, 26(12C14N)−, 27(13C14N)−, as well as interfering mass species associated with a particular mass. However, in cells treated with 13C-labeled phenol the enhancement of signals in masses 25 and 27 images due to increased signals of 25(13C12C)− and 27(13C14N)−, respectively, unequivocally indicated the presence of 13C-labeled phenol in bacterial cells in direct comparison to the samples treated only with unlabeled phenol. The ratio images of masses 25/24 and 27/26 from individual cells revealed a cell-to-cell heterogeneity in the labeling with 13C-phenol. This study indicates that the ion microscope can be applied effectively for studies of labeled molecules in microbiology and biogeochemistry.