MIXOTROPHIC ALGAE CONSTRAIN THE LOSS OF ORGANIC CARBON BY EXUDATION(1)

© 2009 Phycological Society of America.

Détails bibliographiques
Publié dans:Journal of phycology. - 1966. - 45(2009), 4 vom: 01. Aug., Seite 807-11
Auteur principal: Kamjunke, Norbert (Auteur)
Autres auteurs: Tittel, Jörg
Format: Article en ligne
Langue:English
Publié: 2009
Accès à la collection:Journal of phycology
Sujets:Journal Article DOC algae bacteria chemostat competition exudation mixotroph
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520 |a Algae of various taxonomic groups are capable of assimilating dissolved organic carbon (DOC) from their environments (mixotrophy). Recently, we reported that, with increasing biomass of mixotrophs, heterotrophic bacteria did not increase. We hypothesized that algal uptake of external DOC may outweigh their release of DOC by exudation (H1). Here, we addressed an alternative hypothesis that algae did not assimilate external DOC but constrained the release of DOC (H2). In chemostat experiments, we cultured the mixotrophic Chlamydomonas acidophila Negoro together with heterotrophic bacteria. As external substrates, we used glucose, which was potentially available for both bacteria and algae, or fructose, which was available only for bacteria. We increased the biomass of algae by the stepwise addition of phosphorus. Bacterial biomass did not increase in experiments using glucose or when fructose was offered, suggesting that mechanisms other than algal mixotrophy (H1) kept concentrations of bacteria low. Measured exudation rates (percent extracellular release, PER) of mixotrophic algae (Cd. acidophila, Chlorella protothecoides W. Krüger) were very low and ranged between 1.0% and 3.5% at low and moderately high phosphorus concentrations. In contrast, an obligately phototrophic alga (Chlamydomonas segnis H. Ettl) showed higher exudation rates, particularly under phosphorus limitation (70%). The results support H2. If mixotrophy is considered as a mechanism to recycle organic exudates from near the cell surface, this would explain why algae retained mixotrophic capabilities although they cannot compete with bacteria for external organic carbon 
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