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Appl. Environ. Microbiol., Jul 1997, 2735-2740, Vol 63, No. 7
CC Ouverney and JA Fuhrman
Despite the numerous advantages of fluorescent in situ hybridization for
the identification of single prokaryotic cells with 16S rRNA probes, use of
the technique with natural samples, especially those from the marine
environment, is still problematic. The low percentage of fluorescently
labeled cells constitutes the primary problem for in situ hybridization of
natural samples, probably due to low cellular rRNA content. This study
represents an attempt to improve detection of marine prokaryotes by
increasing cellular rRNA content without changing the species composition.
Cells from three California coastal sites were treated with
chloramphenicol, an inhibitor of protein synthesis and rRNA degradation, at
100 (mu)g/ml and then were probed with a "universal" 16S rRNA fluorescent
probe and viewed by image-intensified video microscopy. Counts of
fluorescent cells increased from ca. 75% for untreated samples to ca. 93 to
99% for chloramphenicol-treated samples, compared to counts produced by
DAPI (4(prm1),6-diamidino-2-phenylindole) staining, after at least 45 min
of exposure to the drug (these percentages include autofluorescent cells,
which averaged 6%). This suggests that most cells in these samples were
active. We hypothesize that the low fluorescent-cell counts previously
reported were probably often due to the fluorescence intensity of labeled
cells being below the detection level rather than to high levels of dead
cells in marine environments. This method may aid in the characterization
of bacterioplankton with fluorescent probes.
Copyright © 1997, American Society for Microbiology
Increase in Fluorescence Intensity of 16S rRNA In Situ Hybridization in Natural Samples Treated with Chloramphenicol
Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-0371
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