Ribosomal RNA (rRNA) has been regarded as a proxy for metabolic activityand population growth in microbes, but the limitations and assumptions of thisapproach should be better defined, particularly in eukaryotic microalgae. In thisstudy, the 18S rRNA/rDNA ratio of a marine diatom,Skeletonema tropicum,was examined in batch and semi-continuous cultures subjected to low nitro-gen and phosphorus treatments at a temperature of 20°C. In the semi-contin-uous cultures, the measured 18S rRNA/rDNA ratio ranged from 4.09102to5.09103, and the logarithmic form of this ratio increased linearly with thepopulation growth rate under both low nitrogen and low phosphorus condi-tions. In batch cultures grown under low nitrogen o... More
Ribosomal RNA (rRNA) has been regarded as a proxy for metabolic activityand population growth in microbes, but the limitations and assumptions of thisapproach should be better defined, particularly in eukaryotic microalgae. In thisstudy, the 18S rRNA/rDNA ratio of a marine diatom,Skeletonema tropicum,was examined in batch and semi-continuous cultures subjected to low nitro-gen and phosphorus treatments at a temperature of 20°C. In the semi-contin-uous cultures, the measured 18S rRNA/rDNA ratio ranged from 4.09102to5.09103, and the logarithmic form of this ratio increased linearly with thepopulation growth rate under both low nitrogen and low phosphorus condi-tions. In batch cultures grown under low nitrogen or low phosphorus condi-tions, log (rRNA/rDNA) also increased linearly with growth rate when the latterranged between0.4 and 1.5 day1. The 18S rRNA/rDNA ratios ofSkele-tonemasampled from in the southern East China Sea were substantially lowerthan measured from laboratory cultures. Among the field samples, ratiosobtained at a coastal station were higher than those obtained farther offshore.These results imply higher growth rate at the coastal station, but the influ-ences of other factors, such as cell size and temperature, cannot be ruled out.
