AME 65:129-141 (2011)  -  DOI: https://doi.org/10.3354/ame01535

ABSTRACT: The phylum Planctomycetes is involved in important processes, such as the mineralization of algal biomass and the removal of nitrogen. Using a combination of 16S rRNA sequence analysis and in situ hybridization, we analyzed the diversity and dynamics of Planctomycetes in a shallow meso-eutrophic lake, Lago di Paola, Italy. Planctomycetes detected by the probe PLA46 accounted for 1 to 5% of prokaryotic picoplankton. Abundances were higher in the coastal lake than in the adjacent marine waters. In the surface waters of the lake, the numbers of Planctomycetes fluctuated greatly, reaching a maximum of 1.5 × 10⁶ cells ml⁻¹ in July. The hypoxic bottom waters had less variable cell abundances. The Planctomycetes counts were positively correlated with chlorophyll a concentrations, confirming the role of this phylum in the degradation of algal biomass. We obtained 70 almost full-length 16S rRNA gene sequences of Planctomycetes from 2 libraries. Four distinct clades could be identified. The Pirellula-related group F and the uncultured Planctomycetes group B both had the highest identity with sequences retrieved from marine habitats, whereas the Pirellula-related group E was affiliated with sequences known from freshwater and brackish water environments. The Planctomyces-related group A seems to have a wide habitat range. Catalyzed reported deposition fluorescence in situ hybridization with newly developed probes revealed abundances of the 4 clades in surface and bottom waters ranging from 1 × 10³ to 5 × 10⁴ cells ml⁻¹. Together, the 4 clade-specific probes identified only about a quarter of the Planctomycetes detected by probe PLA46. This indicates that the diversity of Planctomycetes has not yet been fully explored.

KEY WORDS: Coastal lake ecology · Planctomycetes · Bacterial diversity · FISH · CARD-FISH · 16S rRNA gene sequencing