Interactions between a marine dinoflagellate (Alexandrium catenella) and a bacterial community utilizing reverine humic substances

Type Article
Date 1998-10
Language English
Author(s) Carlsoon Per1, Edling Hélène2, Bechemin Christian3
Affiliation(s) 1 : University of Kalmar, lnslitule of Natural Sciences, Dept of Marine Sciences, Box 905, 5·39 129 Kalma r, Sweden
2 : University of Lund, Deparlmenl of Limno logy, Ecology Building. $-22362 Lund, Sweden
3 : IFREMER, BP 5, F-1 7 137 L'Houmeau, France
Source Aquatic Microbial Ecology (0948-3055) (Inter-Research), 1998-10 , Vol. 16 , N. 1 , P. 65-80
DOI 10.3354/ame016065
WOS© Times Cited 42
Keyword(s) Alexandrium catenella, dinoflagellates, bacteria, DOM, humic substances
Abstract

Dissolved organic matter in the form of riverine humic substances stimulated the growth of both axenic nitrogen-limited Alexandrium catenella cultures and nitrogen-limited cultures with a marine bacterial community present. The biomass increase of A. catenella could not be accounted for by utilization of inorganic nitrogen compounds. However, there was a considerable release of dissolved free and combined amino acids from the humic substances that was utilized by A. catenella. About 40% of the nitrogen used by A. catenella in the axenic treatment with humic substances added was taken up as organic nitrogen. Bacterial aminopeptidase and beta -glucosidase activity was stimulated by the addition of humic substances and bacterial growth increased several-fold. Bacteria also utilized the released amino acids from the humic substances, but did not remineralize nitrogen, since no increase in ammonium concentrations could be detected in the bacteria treatments with humic substances added. In the axenic A. catenella treatment there was no significant aminopeptidase activity, suggesting that A. catenella was able to utilize the dissolved combined amino acids directly. Moreover, large fluorescently labeled dextran molecules (2000 kDa) were taken up by A. catenella in the humic treatments, showing up in vacuoles inside the cells. These results suggests that A. catenella can grow well utilizing macromolecular organic compounds containing nitrogen, probably by a direct uptake.

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