Strong coupling between natural Planctomycetes and changes in the quality of dissolved organic matter in freshwater samples

• Published in: FEMS microbiology ecology 2007-03, Vol.59 (3), p.543-555
• Main Author: TADONLEKE, Remy D
• Format: Article
• Language: English
• Subjects: Animals; Bacteria; Bacteria - classification; Bacteria - growth & development; Bacteriology; Bacterioplankton; Biological and medical sciences; Canada; Coupling (molecular); Dilution; Dissolved organic matter; Ecology; Empirical analysis; FISH; Flagellates; Fluorescence; Fluorescence in situ hybridization; Fresh Water - chemistry; Fresh Water - microbiology; Fundamental and applied biological sciences. Psychology; Humic Substances - analysis; Life Sciences; Microbiology; Microbiology and Parasitology; Miscellaneous; Natural waters; Nitrogen; Nutrients; Phosphorus; Phylogeny; Planctomycetes; Plankton - growth & development; Quality; Regrowth; Species Specificity; Water Microbiology
• ISSN: 0168-6496; 1574-6941
• DOI: 10.1111/j.1574-6941.2006.00222.x

Dilution-regrowth experiments coupled to fluorescence in situ hybridization were conducted with samples from two humic reservoirs in order to examine how inorganic nutrients (N, P) affect free-living bacterioplankton phylogenetic groups and subsequently the quality of dissolved organic matter (DOM). The experiments were complemented by analyses of the empirical relationships between the targeted bacteria, nutrients, DOM and grazers. The ratio of absorbance of waters (A) at 250 and 365 nm (A₂₅₀ nm:A₃₆₅ nm), which has been found to increase with the proportion of small molecules in the DOM pool in other humic waters, was used as an index of DOM quality. When nutrient stimulated bacteria, both the responses of bacterial groups (in the absence of grazers) and the ratio A₂₅₀ nm:A₃₆₅ nm were generally different between treatments (+N, +P, +NP), suggesting that in nutrient-poor systems, differences in the type of inorganic nutrient supply will ultimately cause differences in DOM quality. The ratio A₂₅₀ nm,:A₃₆₅ nm peaked in the +N treatments where members of the Planctomycetes (PLA) were the most stimulated group, and across treatments, PLA best explained (positive relationship) variations in this ratio. Consistent with this, the in situ data showed that the removal of the negative effects of flagellates on PLA yielded the highest R² in attempts to use bacterial groups to explain variations in A₂₅₀ nm:A₃₆₅ nm. These findings provide lines of evidence, not previously demonstrated in natural waters, that Planctomycetes may be an important factor changing the DOM quality, particularly in nutrient-poor systems when supplied with inorganic N.