In situ imaging of microorganisms in geologic material

In order to fully delineate the interactions of microorganisms with geologi cal substrates, unequivocal identification of intact microbial cells within geologic samples is required without the disruption of either the rock tex ture or the relationship of the microorganisms to the mineral fabric. To ac hieve this objective we developed a protocol that enables the visualization of intact microbial cells in petrographic thin sections, avoids detaching the cells from their host mineral surfaces and avoids microbial contaminati on during the lapidary process. Propidium iodide and POPO-3, nucleic acid s tains that specifically target double-stranded DNA and RNA were utilized fo r in situ visualization of cells in surface and subsurface basalts from nor theastern Idaho. Additionally, examination of samples incubated with acetic acid-UL-C-14 via phosphor imagining facilitated the in situ visualization of C-14 labeled biomass. Biomass observed was low(<10(7) cells/g). These ob servations indicate that the microbial distribution in these rocks exhibits a high degree of spatial heterogeneity at the sub-centimeter scale. (C) 19 99 Elsevier Science B.V. All rights reserved.