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Appl. Environ. Microbiol., Apr 1997, 1208-1213, Vol 63, No. 4
M Karner and JA Fuhrman
We compared several currently discussed methods for the assessment of
bacterial numbers and activity in marine waters, using samples from a
variety of marine environments, from aged offshore seawater to rich harbor
water. Samples were simultaneously tested for binding to a fluorescently
labeled universal 16S rRNA probe; (sup3)H-labeled amino acid uptake via
autoradiography; nucleoid-containing bacterial numbers by modified DAPI
(4(prm1),6-diamidino-2-phenylindole) staining; staining with
5-cyano-2,3-ditolyl tetrazolium chloride (CTC), a compound supposed to
indicate oxidative cell metabolism; and total bacterial counts (classical
DAPI staining), taken as a reference. For the universal-probe counts, we
used an image intensifying and processing system coupled to the
epifluorescence microscope. All of the above-mentioned methods yielded
lower cell counts than DAPI total counts. Universal-probe counts averaged
about half of the corresponding DAPI count and were highly correlated to
autoradiography counts (r(sup2) = 0.943; n = 7). Nucleoid-containing cell
counts could be lower than DAPI counts by as much as 1 order of magnitude
but sometimes matched autoradiography or probe counts. CTC counts were 2
orders of magnitude below DAPI counts. Universal 16S rRNA probe counts
correlated well with autoradiography results, indicating a population with
at least minimal metabolic activity. The greater variability of the
nucleoid-containing cell counts calls for further investigation of the
processes involved, and CTC counts were well below the range of the other
methods tested.
Copyright © 1997, American Society for Microbiology
Determination of Active Marine Bacterioplankton: a Comparison of Universal 16S rRNA Probes, Autoradiography, and Nucleoid Staining
Department of Biological Sciences, Allan Hancock Foundation, University of Southern California, Los Angeles, California 90089-0371
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