Spatial heterogeneity of crenarchaeal assemblages within mesophilic soil ecosystems as revealed by PCR-single-stranded conformation polymorphism profiling

Microbial ecologists have discovered novel rRNA genes (rDNA) in mesophilic soil habitats worldwide, including sequences that affiliate phylogenetically within the division Crenarchaeota (domain Archaea). To characterize the spatial distribution of crenarchaeal assemblages in mesophilic soil habitats, we profiled amplified crenarchaeal 16S rDNA sequences from diverse soil ecosystems by using PCR-single-stranded-conformation polymorphism (PCR-SSCP) analysis. PCR-SSCP profiles provide a measure of relative microbial diversity in terms of richness (number of different phylotypes as estimated from the number of unique PCR-SSCP peaks) and evenness (abundance of each phylotype as estimated from the relative area under a peak). Crenarchaeal assemblages inhabiting prairie, forest, turf, and agricultural soils were characterized at six sampling locations in southern and central Wisconsin. Phylotype richness was found to be more stable than evenness among triplicate samples collected within 30 cm at each sampling location. Transformation of the PCR-SSCP data by principal-component analysis, followed by statistical testing (analysis of variance [P < 0.0001] and least-significant-difference analysis [alpha = 0.5]), supported the conclusion that each location exhibited a unique profile. To further characterize the spatial distribution of crenarchaeal assemblages at one location, additional soil samples (a total of 30) were collected from agricultural field plots at the Hancock Agricultural Research Station. PCR-SSCP revealed a patchy spatial distribution of crenarchaeal assemblages within and between these plots. This mosaic of crenarchaeal assemblages was characterized by differences in phylotype evenness that could not be correlated with horizontal distance (15 to 30 m) or with depth (0 to 20 cm below the surface). Crenarchaeal 16S rDNA clone libraries were produced and screened for unique SSCP peaks. Clones representing the dominant phylotypes at each location were identified, sequenced, and found to group phylogenetically with sequences in crenarchaeal clade C1b.