Evaluation of Electron Microscopic Techniques to Observe Microbe-Mineral Interactions in Anaerobic Marine Sediments

Marine sediments contain a variety of microorganisms that help determine the local ecosystems and biogeochemistry through their metabolic activities. In anaerobic marine sediments, bacteria use inorganic acceptors to catalyze the oxidation of organic matter. In this study we discuss the advantages and disadvantages of electron microscopic techniques that we have used to study spatial relationships of the microorganisms as well as the location of the minerals within anaerobic sediments from the Santa Barbara Basin, California. Different microscopic techniques have been used to examine the spatial relationships of microbes in marine sediments (1,2,3). Epifluorescence and scanning confocal laser microscopy are useful for the identification and quantification of the living component. However, the study of microbe-mineral interactions needs more resolution to describe the contact between minerals and bacterial cells. To overcome such limitations, we used scanning electron microscopy with back-scattered electron imaging (SEM-BSE). This technique involves the sample preparation to increase the ability of the microorganisms to emit electrons when they are excited by a electron beam and the sedimentological method of embedded the sediments in a resin. The simultaneous application of the X-ray microanalytical system (EDS) permits undisturbed in situ analysis within the marine sediments of the interaction between the microorganisms and the different minerals. The final purpose is the integration a whole set of microscopies to provide an insight into the structure, composition and physical properties of the anaerobic marine sediments at a scale important for microbial ecology. 1 Bernhard JM, Bowser SS. (1996) Novel Epifluorescence Microscopy Method to Determine Life Position of Foraminifera in Sediments. Journal of Micropalaeontology 15:68 2 Bernhard JM, Buck KR, Farmer MA, Bowser SS. (2000) The Santa Barbara Basin is a Symbiosis Oasis. Nature 403:77-80 3 Bernhard JM, Vissher PT, Bowser SS. (2003) Sub-millimiter Life Positions of Bacteria, Protist,and Metazoans in Laminated Sediments of the Santa Barbara Basin. Limnology and Oceanography 48: 813-828.