USE OF CONFOCAL LASER-SCANNING MICROSCOPY ON SOIL THIN-SECTIONS FOR IMPROVED CHARACTERIZATION OF MICROBIAL-GROWTH IN UNCONSOLIDATED SOILS AND AQUIFER MATERIALS

Confocal laser scanning microscopy (CLSM) was utilized to examine samp les from an aquifer microcosm that was used to investigate microbially mediated losses in hydraulic conductivity. Samples were fixed, dehydr ated and dried to prepare the biological material in a fashion similar to that used previously for viewing under the scanning electron micro scope, Then, samples were prepared as thin-sections by employing soil micromorphological techniques. Serial images generated by the CLSM tec hnique were visualized using computer three-dimensional rendering soft ware. Results from the CLSM technique were compared with simple fluore scence microscopy of thin-sections and scanning electron microscopy (S EM) of samples from the microcosm. Computer visualization of serial se ctions with the CLSM technique provided images on a submicron scale in three dimensions. SEM has a much higher resolution, on a nanometer sc ale, but the results are not three dimensional. Artifacts associated w ith thin-section preparation are minimal for natural porous media comp osed mostly of sand, such as aquifer materials. Also, CLSM images are affected minimally by changes to biological material due to sample pre paration, whereas artifacts associated with SEM images are very promin ent, due to the higher magnification and resolution. CLSM of thin-sect ions and SEM are very powerful methods for viewing microbial growth in natural porous media, but CLSM is preferable because it allows three- dimensional visualization and measurements of cells and aggregates wit h few artifacts. (C) 1997 Elsevier Science B.V.