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Aquatic Microbial Ecology

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AME 72:269-280 (2014)  -  DOI:

Individual cell DNA synthesis within natural marine bacterial assemblages as detected by ‘click’ chemistry

Steven Smriga1,2,*, Ty J. Samo1,3, Francesca Malfatti1,4, Joseph Villareal1, Farooq Azam1

1Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0202, USA
2Present address: Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
3Present address: Center for Microbial Oceanography: Research & Education (C-MORE), Department of Oceanography, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA
4Present address: OGS (National Institute of Oceanography and Experimental Geophysics) Oceanography Section (OCE), 34151 Santa Croce, Trieste, Italy
*Corresponding author:

ABSTRACT: Individual cell growth rates enhance our understanding of microbial roles in regulating organic matter flux in marine and other aquatic systems. We devised a protocol to microscopically detect and quantify bacteria undergoing replication in seawater using the thymidine analog 5-ethynyl-2’-deoxyuridine (EdU), which becomes incorporated into bacterial DNA and is detected with a ‘click’ chemistry reaction in <1 h. Distinct EdU localization patterns were observed within individual labeled cells, e.g. some displayed 2 or more distinct EdU loci within a single DAPI-stained region, which likely indicated poleward migration of nascent DNA during the early phase of replication. Cell labeling ranged from 4.4 to 49%, comparable with cell labeling in parallel incubations for 3H-thymidine microautoradiography. Meanwhile, EdU signal intensities in cells ranged >3 orders of magnitude, wherein the most intensely labeled cells comprised most of a sample’s sum community EdU signal, e.g. 26% of cells comprised 80% of the sum signal. This ability to rapidly detect and quantify signals in labeled DNA is an important step toward a robust approach for the determination of single-cell growth rates in natural assemblages and for linking growth rates with microscale biogeochemical dynamics.

KEY WORDS: Single cell growth · Click chemistry · Marine bacteria · Microradiography · Epifluorescence microscopy · BrdU

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Cite this article as: Smriga S, Samo TJ, Malfatti F, Villareal J, Azam F (2014) Individual cell DNA synthesis within natural marine bacterial assemblages as detected by ‘click’ chemistry. Aquat Microb Ecol 72:269-280.

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