Beschreibung:
<jats:title>Summary</jats:title><jats:p>The rate of [<jats:sup>3</jats:sup>H‐methyl] thymidine (<jats:sup>3</jats:sup>H‐TdR) incorporation into DNA has been applied extensively to measure cell production by bacterial communities in aquatic environments. Here we describe a method to quantify <jats:sup>3</jats:sup>H‐TdR incorporation by specific, phylogenetically defined members of the bacterial community. The method involves selectively capturing DNA from targeted groups of bacteria and then quantifying its <jats:sup>3</jats:sup>H radioactivity. The method was applied to measure <jats:sup>3</jats:sup>H‐TdR incorporation by the members of the phylum <jats:italic>Bacteriodetes</jats:italic> whose members, which include the <jats:italic>Cytophaga</jats:italic>‐<jats:italic>Flavobacter</jats:italic> cluster, are ubiquitous in coastal waters. <jats:sup>3</jats:sup>H‐labelled DNA from <jats:italic>Bacteriodetes</jats:italic> was selectively biotinylated in PCR‐like reactions that contained a <jats:italic>Bacteriodetes</jats:italic>‐specific 16S rRNA gene primer, thermostable DNA polymerase and biotinylated dUTP. The biotinylated DNA was then captured on streptavidin‐coated beads and its <jats:sup>3</jats:sup>H radioactivity determined by scintillation counting. We have termed this method ‘selective nucleic acid polymerase‐biotinylation and capture’ or ‘SNAP‐BAC’. Internal <jats:sup>33</jats:sup>P‐labelled DNA standards were used to quantify the recovery of <jats:sup>3</jats:sup>H‐labelled DNA from the SNAP‐BAC reactions. The method was verified by successfully targeting <jats:italic>Bacteriodetes</jats:italic> in simple laboratory mixtures of <jats:sup>3</jats:sup>H‐labelled DNA extracted from pure cultures of <jats:italic>Bacteriodetes</jats:italic> and γ‐proteobacteria. Field application of this method in Puget Sound and off the Washington coast determined that <jats:italic>Bacteriodetes</jats:italic> were responsible for 56 ± 17% and 32 ± 5% of community <jats:sup>3</jats:sup>H‐TdR incorporation (1.3 ± 0.3 and 9.9 ± 1.7 pmol l<jats:sup>−1</jats:sup> h<jats:sup>−1</jats:sup>) at these two locations.</jats:p>