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The effects of N:P ratio and nitrogen form on four major freshwater bacterial taxa in biofilms

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Bacteria in freshwater systems play an important role in nutrient cycling through both assimilatory and dissimilatory processes. Biotic and abiotic components of the environment affect these transformations as does the stoichiometry of the nutrients. We examined responses of four major taxa of bacteria in biofilms subjected to various N:P molar ratios using either nitrate or ammonium as a nitrogen source. Fluorescent in situ hybridization was used to enumerate the Domain bacteria as well as the α-, -, and -proteobacteria, and the Cytophaga-Flavobacteria cluster. Generally, bacterial responses to the treatments were limited. However, the Cytophaga-Flavobacteria and -proteobacteria both responded more to the ammonium additions than nitrate, whereas, the α-proteobacteria responded more to nitrate additions. The -proteobacteria also exhibited peak relative abundance at the highest N:P ratio. Nutrient concentrations were significantly different after the incubation period, and there were distinct changes in the stoichiometry of the microcosms with ammonium. We demonstrated that bacteria may play an important role in nutrient uptake, and transformation, and can have a dramatic effect on the nutrient stoichiometry of the surrounding water. However, although some taxa exhibited differences in response to ammonium and nitrate, the impact of nutrient stoichiometry on the abundance of the taxa examined was limited.

Les bactéries présentes dans les systèmes d’eau douce jouent un rôle important dans le cycle des nutriments par des processus assimilatoires et dissimilatoires. Les composantes biotiques et abiotiques de l’environnement affectent ces transformations, tout comme la stoechiométrie des nutriments. Nous avons examiné les réponses de quatre taxons majeurs de bactéries en biofilms, soumis à des ratios molaires N:P variés, qui utilisent soit le nitrate ou l’ammonium comme source d’azote. Une hybridation fluorescente in situ a été utilisée pour énumérer les Eubactéries, les α-, - et -protéobactéries, ainsi que la grappe Cytophaga-Flavobacteria. Généralement, les réponses bactériennes aux traitements étaient limitées. Cependant, les Cytophaga-Flavobacteria et les -protéobactéries répondaient davantage aux ajouts d’ammonium que de nitrate, alors que les α-protéobactéries répondaient davantage aux ajouts de nitrate. Les -protéobactéries montraient aussi un pic d’abondance relative au ratio N : P le plus élevé. Les concentrations de nutriments étaient significativement différentes après la période d’incubation et il existait des changements distincts dans la stoechiométrie des microcosmes avec l’ammonium. Nous avons démontré que les bactéries pourraient jouer un rôle important dans la captation et la transformation des nutriments et qu’elles pourraient avoir un effet dramatique sur la stoechiométrie des nutriments des eaux environnantes. Cependant, même si quelques taxons montrent des différences de réponses à l’ammonium et au nitrate, l’impact de la stoechiométrie des nutriments sur l’abondance des taxons examinés était limité.

Document Type: Research Article

Publication date: 2010-01-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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