METHODS AND PLATFORMS 



Research strategy: Measurements of rRNA content targeted to dominant members of 

 bacterial community. Implementation of cooled-CCD camera/image analysis system to increase 

 sensitivity and sampling throughput. 



Rationale: Empirical relationship between rRNA and growth rate; control of bacterial 

 gTowth rate seems to be interpreted through regulation of rRNA synthesis and concentration. 



STRENGTHS AND LIMITATIONS OF PROPOSED RESEARCH 



Sensitivity and limitations: Currently rRNA is measured in 100-ribosome increments 

 starting at 100-200 ribosomes per cell. This includes ca. 2/3 of all cells in field samples. 

 Cooled-CCD camera with image analysis will be more sensitive. Currently, multiple probes are 

 used, but it will probably not be practical to design more than 2-3 probes specific to a given 

 taxon. The method will probably not be useful for measuring rRNA in the least active cells in 

 the field. 



Other information: Need hydrography, chl, 2 , DOC, nutrients to interpret bacterial 

 growth as a consequence of these properties. A measure of labile DOC could be especially 

 useful. Need direct respiration measurements to constrain growth rate estimates. 



STATUS OF RESEARCH 



Status: Concept is proven and procedures have been applied in field studies. Program is 

 now focusing on learning to interpret the data. Next applied goal is implementation of 

 taxon- specific measurements in mixed communities (primarily design and testing of probes). We 

 measure rRNA in individual cells, however, the rRNA-frequency data are entirely new and we 

 have no notion how to interpret them as yet. 



Caveats: RNA:growth rate relationship is not constant. We are not sure yet what 

 influences the relationship; current efforts are focused on RNA regulatory behavior, taxon-specific 

 differences, biovolume effects, and temperature. Available field data point to taxon-specific 

 applications rather than any universal application to whole bacterial communities. 



Keywords: microbial, growth, rRNA 



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