High-resolution electron microscope (EM) images greatly magnify microbes and their microhabitats, and reveal minute features of microbial cells and their material surroundings. EM images potentially are of great use in studying how microbes interact with natural and man-made materials. However, the many types of microorganisms co-existing in natural samples typically cannot be distinguished from one another based on appearance alone. Furthermore, when "zoomed out" it is not possible to see the overall distribution of microbes in EM-mounted samples. A means of visually distinguishing specific genetic types of microbes in EM images must be invented to fully exploit the potential of electron microscopy for learning about in situ microbial distribution and activity in the environment. A grant has been awarded to Profs. Rachel M. Haymon and Patricia Holden at University of California, Santa Barbara, and to Dr. Stefan Sievert at Woods Hole Oceanographic Institution, for development of metallic "tags" that will attach to DNA sequences of selected microbes. When the metals are excited by electron beams used to generate EM images, the metals will emit X-rays and permit unambiguous visual identification of the targeted organisms at both high and low magnifications. This method will solve the existing problems in distinguishing spatial distributions and identities of microbes imaged with electron beams, and will make it possible to understand associations of microbes and minerals at small scales that are relevant to microbial life.
Applications of the proposed metal-tagged DNA probes to understanding how microbes interact with the environment are vast. It is expected that the proposed method will become a standard tool for studying the function, ecology, and environmental impact of microbial activities in natural environments. For example, Drs. Haymon, Holden, and Sievert hope to apply this new technique to studies of microbes in soils, where microbes are important to biodegradation of toxic anthropogenic compounds, and in hydrothermal systems, where microbes interact with geologic materials under extreme thermal and chemical conditions.
