Stable Isotope Probing Links Taxonomy with Function in Microbial Communities Microbial ecologists have a culture-independent means for analyzing sources of metabolic activities among complex mixtures of microbes

S table isotope probing (SIP) is proving to be a powerful tool for molecular microbial ecologists, providing a culture-independent means of investigating populations that conduct particular metabolic processes in specific environments. Moreover, this alternative means for linking taxonomic identity with function may also assist microbiologists in developing strategies for isolating elusive microorganisms that are involved in biogeochemical processes. One approach relies on density gradient centrifugation to separate organisms on the basis of having different guanidine-cytosine (GC) contents. Furthermore, with steadily increasing availability of C-enriched substrates and the potential of using other isotopes such as N, microbial ecologists can now address challenging questions surrounding natural processes.