SURFACE-ENHANCED INFRARED ABSORPTION-REFLECTANCE (SEIRA) MICROSPECTROSCOPY FOR BACTERIA LOCALIZATION ON GEOLOGIC MATERIAL-SURFACES

Surface-enhanced infrared absorption-reflectance (SEIRA) microspectros copy is potentially a useful chemical/biological probe to provide insi ghts into the localization of living endolithic bacteria on the surfac es of geologic materials. This hypothesis was tested by validating and demonstrating the use of SEIRA with a metal-overlayer configuration t i, identify qualitatively on vesicular basalt surfaces the highly loca lized differences in the chemical composition and in the structure of clusters of endolithic bacteria, vesicles, and minerals. The metal-ove rlayer configuration was achieved by evaporating a thin gold-film on b asalt specimen surfaces. Fourier-transform SEIRA microspectra of the s pecimen surfaces were recorded in the 650-4000 cm(-1) infrared region at a resolution of 4 cm(-1) on a Fourier-transform infrared spectromet er coupled to an infrared microscope. All bacteria-inhabiting surfaces exhibited infrared absorption bands indicative of bacterial cells, ba nds that became ideal biomarkers by which to detect the presence of ba cteria. All basalt surfaces exhibited infrared absorption bands indica tive of silicates, bands that became ideal mineral markers by which to detect the presence of silicate-containing minerals and locations of vesicles (gas-bubble cavities). Comparative analysis of space-resolved microspectra suggested that bacteria in the vesicular basalt lived no t only on the vesicle surface but that they also penetrated and lived beneath the vesicle surface. The penetration terminated when calcic-pl agioclase feldspar became the dominant constituent mineral in the vesi cular basalt. With this experimental effort, the practical aspects and the usefulness of SEIRA as a promising tool to complement existing te chniques for studying the in-situ localization of living bacteria in g eologic materials have been demonstrated. (C) 1998 Elsevier Science B. V. All rights reserved.