Editor: Riks Laanbroek
Active bacteria and archaea cells fixing bicarbonate in the dark along the water column of a stratified eutrophic lagoon
Article first published online: 20 MAY 2011
© 2011 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved
FEMS Microbiology Ecology
Volume 77, Issue 2, pages 370–384, August 2011
How to Cite
Llirós, M., Alonso-Sáez, L., Gich, F., Plasencia, A., Auguet, O., Casamayor, E. O. and Borrego, C. M. (2011), Active bacteria and archaea cells fixing bicarbonate in the dark along the water column of a stratified eutrophic lagoon. FEMS Microbiology Ecology, 77: 370–384. doi: 10.1111/j.1574-6941.2011.01117.x
Present addresses: Marc Llirós, Laboratory of Freshwater Ecology, Research Unit in Organismic Biology, Department of Biology, University of Namur, B-5000 Namur, Belgium. Laura Alonso-Sáez, Centro Oceanográfico de Gijón-IEO, E-33212, Gijón, Spain.
- Issue published online: 11 JUL 2011
- Article first published online: 20 MAY 2011
- Accepted manuscript online: 21 APR 2011 06:52AM EST
- Received 24 January 2011; revised 13 April 2011; accepted 14 April 2011., Final version published online 20 May 2011.
- dark carbon fixation;
- sulfidic redoxclines;
- anaplerotic reactions;
- heterotrophic carbon fixation;
- karstic lakes
We studied the carbon dioxide fixation activity in a stratified hypereutrophic karstic lagoon using a combination of fingerprinting techniques targeting bacterial and archaeal 16S rRNA genes, functional gene cloning [the acetyl-CoA carboxylase (accC)], and isotopic labelling (14C-bicarbonate) coupled to single-cell analyses [microautoradiography combined with catalyzed reported deposition-FISH (MAR-CARD-FISH)]. The microbial planktonic community was dominated by bacteria with maximal abundances of archaea just below the oxic/anoxic transition zone (7% of total cells). In situ incubations with radiolabelled bicarbonate showed maximal photoassimilation activity in the oxic epilimnion, whereas dark CO2 fixation was consistently observed throughout the water column, with a maximum at the oxic/anoxic interface (8.6 mg C m−3 h−1). The contributions of light and dark carbon fixation activities in the whole water column were 69% and 31% of the total C incorporated, respectively. MAR-CARD-FISH incubations corroborated these results and revealed that the highest fraction of bacterial and archaeal cells actively uptaking bicarbonate in the light was found at the surface. The bacterial community was mainly composed of green sulfur bacteria (Chlorobi) and members of the Betaproteobacteria and the Bacteroidetes. The archaeal assemblage was composed of phylotypes of the Miscellaneous Crenarchaeotic Group and a few methanogens. Clone libraries of the accC gene showed an absolute dominance of bacterial carboxylases. Our results suggest that the dark carbon fixation activity measured was mainly related to CO2 incorporation by heterotrophs rather than to the activity of true chemoautotrophs.