are especially useful for dissecting community structure, because 

 they can identify species in mixed, natural communities without the 

 need to subculture or grow the organisms in the laboratory. 

 Nucleic acid hybridization technigues also can be used to identify 

 and localize individual cells. Binding of probes in cells can be 

 detected by epifluorescence microscopy or flow cytometry. The use 

 of in situ probes has a great potential for elucidating the spatial 

 relationships of microbial organisms which exist in complex, 

 interdependent consortia. Immunological technigues also can 

 identify organisms, either to species level or to a functional 

 group level. 



While the aforementioned technigues can be, and to some extent 

 are being, used to objectively and rapidly document genetic 

 diversity within natural ecosystems, the underlying causes and 

 mechanisms of genetic change remain obscure. Resolving this issue 

 is central to understanding how genetic change is related to 

 environmental perturbation. Experimentally, the causality of 

 genetic change is presently best addressed in a laboratory, where 

 organisms can be manipulated to study factors which influence the 

 rates of genetic mutation and how these rates affect community 

 stability. As environments change, there is a need to know how 

 populations, both starved (dormant) and actively growing 

 populations, adapt genetically and how this adaptability is related 

 to the functional resistance or resilience of the populations. 



Thus, the molecular focus of questions related to community 

 structure and stability is primarily on the causes and effects of 

 external environmental factors, and how they affect genetic change. 

 Molecular biological technigues can rapidly and precisely detect 

 mutations; however, it is unclear how the natural rate of mutation 

 and selection can be differentiated from an environmentally 

 accelerated rate. 



There is some indication that chronic environmental stress can 

 increase the mutation rate in some microbes. This effect could be 

 important in increasing the adaptability of populations by 

 increasing genetic variability. The mechanisms for this phenomenon 

 are obscure; although it has been well documented in model 

 organisms such as Escherichia coli , it is unclear how far the 

 findings can be generalized. Is there historical evidence for 

 increased genetic variability in response to environmental change? 

 For example, pollen DNA from extant species can be assayed for 



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