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Applied and Environmental Microbiology, December 2000, p. 5448-5456, Vol. 66, No. 12
Center for Microbial
Ecology1 and Departments of Crop and
Soil Sciences and Microbiology,2 Michigan
State University, East Lansing, Michigan 48824
Received 18 April 2000/Accepted 1 September 2000
Fluorescent Pseudomonas strains were isolated from 38 undisturbed pristine soil samples from 10 sites on four continents. A
total of 248 isolates were confirmed as Pseudomonas sensu
stricto by fluorescent pigment production and group-specific 16S
ribosomal DNA (rDNA) primers. These isolates were analyzed by three
molecular typing methods with different levels of resolution: 16S rDNA
restriction analysis (ARDRA), 16S-23S rDNA intergenic
spacer-restriction fragment length polymorphism (ITS-RFLP) analysis,
and repetitive extragenic palindromic PCR genomic fingerprinting with a
BOX primer set (BOX-PCR). All isolates showed very similar ARDRA
patterns, as expected. Some ITS-RFLP types were also found at every
geographic scale, although some ITS-RFLP types were unique to the site
of origin, indicating weak endemicity at this level of resolution.
Using a similarity value of 0.8 or more after cluster analysis of
BOX-PCR fingerprinting patterns to define the same genotypes, we
identified 85 unique fluorescent Pseudomonas genotypes in
our collection. There were no overlapping genotypes between sites as
well as continental regions, indicating strict site endemism. The
genetic distance between isolates as determined by degree of
dissimilarity in BOX-PCR patterns was meaningfully correlated to
the geographic distance between the isolates' sites of origin. Also, a
significant positive spatial autocorrelation of the distribution of the
genotypes was observed among distances of <197 km, and significant
negative autocorrelation was observed between regions. Hence, strong
endemicity of fluorescent Pseudomonas genotypes was
observed, suggesting that these heterotrophic soil bacteria are not
globally mixed.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Biogeography and Degree of Endemicity of
Fluorescent Pseudomonas Strains in Soil
*
Corresponding author. Mailing address: Center for
Microbial Ecology, Plant and Soil Science Bldg., Michigan State
University, East Lansing, MI 48824. Phone: (517) 353-9021. Fax: (517)
353-2917. E-mail: tiedjej{at}msu.edu.
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