It is now widely accepted that many ecologically important microorganisms
are uncultured. For example, examination of microbial communities of various
Arizona soils concluded that of the organisms detected, seven bacterial
divisions were represented among the uncultured organisms versus three for
cultured isolates (Dunbar et al., 1999). The focus of much SIP work has
been on the prospect of discovering the role of heretofore uncultivated
organisms in important processes, however, it is likely that some of the
organisms we already know about (or their close relatives) are also important
in key functions in the environment. SIP can thus be just as useful in
examining the behavior of organisms (regardless of novelty) in response to
various stimuli, which may provide practical insight into key microbial
functions, perhaps leading to improved environmental or agricultural
management. This review examines the most common forms of SIP used in
soil microbiology, describes some of the findings that have been obtained
using these approaches, and suggests fruitful directions for the application of
SIP to soils research.