Zubkov¹, Mikhail V., Bernhard M. Fuchs², Glen A. Tarran³, Peter H. Burkill¹ and Rudolf Amann²

¹Southampton Oceanography Centre, Southampton SO14 3ZH, United Kingdom, Tel: +44 (0)2380 596335, Fax: +44 (0)2380 596247, E-mail: mvz@soc.soton.ac.uk, ²Max-Planck-Institute for Marine Microbiology, D-28359 Bremen, Germany, and ³Plymouth Marine Laboratory, Plymouth PL1 3DH, United Kingdom

High uptake of organic nitrogen compounds by Prochlorococcus cyanobacteria as a key to their dominance in oligotrophic oceanic waters

Direct evidence is reported that marine unicellular cyanobacteria take up organic nitrogen compounds in situ at high rates. About 33% of total bacterioplankton turnover of amino acids, determined using a representative ³⁵S-methionine precursor and flow sorting, can be assigned to Prochlorococcus and 3% assigned to Synechococcus in the oligotrophic and mesotrophic parts of the Arabian Sea, respectively. This finding may provide a mechanism for Prochlorococcus competitive dominance over both strictly autotrophic algae and other bacteria in oligotrophic regions sustained by nutrient remineralisation via a microbial loop.