Microbial activities on Trichodesmium colonies

Abstract

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 Tr~chodesrnium spp. were investigated. Thymidine incorporation rates between 0.011 and 0.045 pm01 h-' colony-' and leucine incorporation between 0.007 and 0 332 pm01 h-' colony-' were found. Turnover times of glucose varied between 31 and 267 d colony-' The hydrolysis rates (Hr) determined a t trace concentrations of substrates ranged between 0.88 and 16.92 %, h ' colony ' ' for phosphatase activities, between 0.01 and 0.87 ,l h-' co lony1 for a-glucosidase activities, between 0.03 and 1.24% h-' colony-' for P-glucosidase activities, between 0.02 and 0.58% h' colony-' for P-glucos a m ~ n ~ d a s e activity, and between 0.40 and 7.601, h-' colony-' for leuclne peptidase activities, respectlvely. The quotient of glucose turnover and hydrolysis rate suggests that large quantltles 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 pm01 h' I-' and for leucine incorporation between 21.44 and 127.67 pm01 h ' I ' The turnover time of glucose of free living bacteria was between 24 and 109 d . Since abundance of colonles was approxin~ately 7 colonies I ' , this indicates that the activity of free living bacteria was substantially higher than that of attached bacteria on Tr~chodesm~um colonies in the same volume of water