COMPARISON OF NUCLEIC-ACID HYBRIDIZATION AND FLUOROMETRY FOR MEASUREMENT OF THE RELATIONSHIP BETWEEN RNA DNA RATIO AND GROWTH-RATE IN A MARINE BACTERIUM/

Continuous culture of Pseudomonas stutzeri Zobell, a marine denitrifyi ng bacterium, was used to determine the relationship between growth ra te and nucleic acid content. The trend of decreasing RNA content with decreasing growth rate, well known for enteric organisms, was found to occur in P. stutzeri Zobell as well, even at very long generation tim es such as those thought to occur in the oligotrophic ocean. When assa yed by ethidium bromide fluorescence, the total RNA/DNA ratio was line ar for generation times between 6 and 60 h. We also developed a 200-bp nucleic acid probe (with species-specific potential) for a portion of the 23S rRNA gene of P. stutzeri Zobell, which was used to quantify r RNA and rDNA by hybridization in the same continuous cultures. The rRN A/rDNA ratio also exhibited a decrease with decreasing growth rate, bu t the relationship, although significant, was not simply linear. The s ensitivity and accuracy of the two methods are compared, and the poten tial for species specificity in future hybridizations is discussed.