MEPS 141:173-181 (1996)  -  doi:10.3354/meps141173

Microbial activities on Trichodesmium colonies

Nausch M

During a cruise from 20 May to 19 June 1994 in the tropical North Atlantic Ocean between 30 and 10°N and in the Caribbean Sea, heterotrophic bacterial activities on colonies of the filamentous cyanobacterium Trichodesmium spp. were investigated. Thymidine incorporation rates between 0.011 and 0.045 pmol h-1 colony-1 and leucine incorporation between 0.007 and 0.332 pmol h-1 colony-1 were found. Turnover times of glucose varied between 31 and 267 d colony-1. The hydrolysis rates (Hr) determined at trace concentrations of substrates ranged between 0.88 and 16.92% h-1 colony-1 for phosphatase activities, between 0.01 and 0.87% h-1 colony-1 for alpha-glucosidase activities, between 0.03 and 1.24% h-1 colony-1 for beta-glucosidase activities, between 0.02 and 0.58% h-1 colony-1 for beta-glucosaminidase activity, and between 0.40 and 7.60% h-1 colony-1 for leucine peptidase activities, respectively. The quotient of glucose turnover and hydrolysis rate suggests that large quantities of released matter were not taken up by adherent bacteria. Most likely this dissolved material diffuses into the surrounding water and is available for free living bacteria. Thymidine incorporation of free living bacteria in surrounding water ranged between 0.977 and 18.49 pmol h-1 l-1 and for leucine incorporation between 21.44 and 127.67 pmol h-1 l-1. The turnover time of glucose of free living bacteria was between 24 and 109 d. Since abundance of colonies was approximately 7 colonies l-1, this indicates that the activity of free living bacteria was substantially higher than that of attached bacteria on Trichodesmium colonies in the same volume of water.

Trichodesmium · Cyanobacteria · Bacterial degradation · Thymidine incorporation · Leucine incorporation · Extracellular enzyme activity

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