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Applied and Environmental Microbiology, April 1999, p. 1753-1761, Vol. 65, No. 4
Department of Veterinary Microbiology,
Received 26 October 1998/Accepted 4 January 1999
A fluorescence in situ hybridization (FISH) technique based on
binding of a rhodamine-labelled oligonucleotide probe to 16S rRNA was
used to estimate the numbers of ribosome-rich bacteria in soil samples.
Such bacteria, which have high cellular rRNA contents, were assumed to
be active (and growing) in the soil. Hybridization to an rRNA probe,
EUB338, for the domain Bacteria was performed with a soil
slurry, and this was followed by collection of the bacteria by membrane
filtration (pore size, 0.2 µm). A nonsense probe, NONEUB338 (which
has a nucleotide sequence complementary to the nucleotide sequence of
probe EUB338), was used as a control for nonspecific staining. Counting
and size classification into groups of small, medium, and large
bacteria were performed by fluorescence microscopy. To compensate for a
difference in the relative staining intensities of the probes and for
binding by the rhodamine part of the probe, control experiments in
which excess unlabelled probe was added were performed. This resulted in lower counts with EUB338 but not with NONEUB338, indicating that
nonspecific staining was due to binding of rhodamine to the bacteria. A
value of 4.8 × 108 active bacteria per g of dry soil
was obtained for bulk soil incubated for 2 days with 0.3% glucose. In
comparison, a value of 3.8 × 108 active bacteria per
g of dry soil was obtained for soil which had been air dried and
subsequently rewetted. In both soils, the majority (68 to 77%) of
actively growing bacteria were members of the smallest size class (cell
width, 0.25 to 0.5 µm), but the active (and growing) bacteria still
represented only approximately 5% of the total bacterial population
determined by DAPI (4',6-diamidino-2-phenylindole) staining. The FISH
technique in which slurry hybridization is used holds great promise for
use with phylogenetic probes and for automatic counting of soil bacteria.
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Counting and Size Classification of Active Soil
Bacteria by Fluorescence In Situ Hybridization with an rRNA
Oligonucleotide Probe
*
Corresponding author. Mailing address: Department of
Veterinary Microbiology, Royal Veterinary and Agricultural University, Stigbøjlen 4, 1870 Frederiksberg C, Denmark. Phone: 4535282783. Fax:
4535282757. E-mail: kvlhc{at}unidhp.uni-c.dk.
Applied and Environmental Microbiology, April 1999, p. 1753-1761, Vol. 65, No. 4
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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