AME 75:91-102 (2015)  -  DOI:

Nutrient and enzymatic adaptations of stream biofilms to changes in nitrogen and phosphorus supply

Joan Artigas1,2,*, Anna M. Romaní3, Sergi Sabater3,4 

1Clermont Université, Université Blaise Pascal, Laboratoire Microorganismes: Génome et Environnement, BP 10448, 63000 Clermont-Ferrand, France
2CNRS, UMR 6023, LMGE, 63177 Aubière, France
3Institute of Aquatic Ecology, Faculty of Sciences, University of Girona, Campus Montilivi, 17071 Girona, Spain
4Catalan Institute for Water Research (ICRA), H2O Building, Scientific and Technological Park of the University of Girona, Emili Grahit, 101, 17003 Girona, Spain

ABSTRACT: We evaluated the effect of high and low nutrient nitrogen (N) and phosphorus (P) concentrations (Hn and Ln, respectively) and N:P supply (16:1 and 56:1, respectively) on the structure and activity of stream biofilms. Natural biofilms were exposed to 4 different nutrient conditions (16:1-Hn, 16:1-Ln, 56:1-Hn, 56:1-Ln) in a microcosm experiment in the laboratory over 35 d. Biofilm bacterial density and chlorophyll a (chl a) concentration decreased under lower N and P concentrations. Bacterial density was further sensitive to nutrient imbalance and decreased with decreasing P availability, while chl a concentration was not affected by P reduction. Greater P requirements and weaker ability to store large quantities of P in bacteria compared to algae may explain these differences. Biofilm responses to imbalanced N:P (56:1) were only observed under Hn conditions, and were expressed as an increase in the proportion of algal carbon with respect to bacterial carbon, and greater N and extracellular polymeric substance (EPS)-polysaccharide accumulation. Algae withstood N:P imbalance better than bacteria under Hn conditions, but this trend decreased at low water nutrient concentration (56:1-Ln condition). The cellobiohydrolase:phosphatase enzyme activity ratio was negatively correlated to the biofilm C:P molar ratio, evidencing the tight link between nutrient acquisition and storage in biofilms. Our experiment highlighted the rapid adaptation (3 to 28 d) of biofilm nutrient content and enzyme activities to changes in water nutrient availability.

KEY WORDS: Ecoenzymatic stoichiometry · Algae · Bacteria · N:P imbalance · Nutrient limitation

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Cite this article as: Artigas J, Romaní AM, Sabater S (2015) Nutrient and enzymatic adaptations of stream biofilms to changes in nitrogen and phosphorus supply. Aquat Microb Ecol 75:91-102.

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