collected quickly, without fractionation and disruption of 

 consortia, and would be fixed or otherwise "frozen." Second, the 

 samples could then be stored long enough for transport to a 

 laboratory; that is, it would not be necessary to carry out complex 

 analysis in an inconvenient location (e.g., aboard ship or in a 

 forest) . Third, the method would analyze growth rates in single 

 cells in a species or in a group-specific manner so that different 

 growth rates by different components of a consortium or community 

 could be discerned. Fourth, the method should be broadly 

 applicable to a variety of organisms. 



Two possible molecular approaches are given here as 

 illustrations. The first example is an estimation of growth rates 

 from the ratio of ribosomal RNA (or some measure of ribosomes) to 

 DNA of single cells. Consider two fluorescent probes (which can be 

 differentiated by emission wavelength) ; one hybridizes to the rRNA 

 of a particular species or genus, and the other hybridizes to some 

 chromosomal DNA segment. The sample containing the consortium or 

 population is fixed to a slide, permeabilized, and then probed with 

 the rRNA and DNA probes. Then, the fluorescence of the two probes 

 is measured separately by fluorescence microscopy (a microscope 

 fitted with a detector to quantitate light emissions and supporting 

 image-processing software) or flow cytometry. The ratios of more 

 than one type of organism could be measured simultaneously if more 

 fluorescent labels were available. This type of approach could 

 simultaneously estimate the growth rates of different members of a 

 consortium while preserving the geometry of the consortium. 

 Developing and using new methods to elucidate metabolic activities 

 and growth rates in nature is a high priority. 



A second approach would be to use the polymerase chain 

 reaction (PCR) to detect messenger RNAs in cells and find mRNAs or 

 proteins that could be used as indicators of growth. Preliminary 

 evidence suggests that some mRNAs and proteins are expressed 

 preferentially as bacteria shift from rapid to slower rates of 

 growth. In eucaryotes, cell cycle-specific proteins are well 

 documented. The activity of cell processes could be associated 

 with such mRNAs and proteins, and probes and antibodies could be 

 used in cross-sections or smears from natural samples. 



A special subset of the issue of biochemical flux is that of 

 the maintenance energy of cells: namely, that portion of the 



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