Growth rates of abundant marine bacterial clades in pure cultures and in the Delaware estuary
Lankiewicz, Thomas St. Julien
University of Delaware
Ratios of 16S rRNA to 16S rRNA genes (rRNA:rDNA) have been used to assess the contribution of bacterial taxa to total community growth and carbon cycling. However, interpretations of rRNA:rDNA ratios is based upon a limited number of studies with rapidly growing bacteria. The most abundant bacteria in the oceans probably grow more slowly than those bacteria whose rRNA:rDNA versus growth rate relationships are known. To understand how rRNA:rDNA varies in abundant marine bacteria, I used quantitative PCR and reverse transcriptase quantitative PCR to measure rRNA:rDNA in bacteria known to be abundant in coastal Delaware waters and elsewhere. Four marine isolates were examined including Ca . Pelagibacter ubique HTCC1062, a coastal isolate of SAR11, the most abundant bacterial clade in the oceans. In culture, there were significant relationships between rRNA:rDNA and growth rate for some strains but not for others. The rRNA:rDNA ratios determined along a transect in the Delaware estuary suggested that oligotrophic bacteria grew up to ten-fold faster than copiotrophic bacteria in the same communities. I find that rRNA:rDNA ratios can be useful for estimating growth rates in some bacterial taxa and that knowledge of the rRNA:rDNA versus growth rate relationship for a given taxon can enhance interpretations of rRNA:rDNA data from natural communities.