JPR Advance Access published online on November 17, 2007
Journal of Plankton Research, doi:10.1093/plankt/fbm091
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Differential microbial uptake of dissolved amino acids and amino sugars in surface waters of the Atlantic Ocean
1 National Oceanography Centre, Southampton, European Way, Southampton SO14 3ZH, United Kingdom 2 Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth PL1 3DH, United Kingdom 3 Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, D-28359 Bremen, Germany
* Corresponding author mailing address: National Oceanography Centre, Southampton European Way Southampton, SO17 3ZH United Kingdom Telephone: +44 (0)23 8059 6335 Fax: +44 (0)23 8059 6247 E-mail: mvz{at}noc.soton.ac.uk
Received on May 10, 2007; revised on October 25, 2007; accepted on October 15, 2007
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Abstract |
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Nitrogen bioavailability is considered to limit productivity of oceanic oligotrophic gyres, the largest biomes on Earth. In order to assess the microbial requirement for small organic nitrogen molecules in these and other waters the microbial uptake rates of amino acids (leucine, methionine, tyrosine) and amino sugars (glucosamine, N-acetyl-glucosamine) as well as glucose were compared using a bioassay technique of radiotracer dilution. The bioassays were carried out on four mid-Atlantic meridional transects spanning a latitudinal range from 60oN to 42oS. The mean concentrations of both bioavailable N-acetyl-glucosamine and glucose in the gyres were 1 nM, four times higher than the mean leucine concentration. Despite its lower concentration, the mean turnover time of leucine in the gyres of 15 hours was 90 and 9 times shorter than the turnover time of N-acetyl-glucosamine and glucose, respectively. In addition, among amino acids, leucine was taken up in the gyres at a rate 1.5 times faster than methionine and 2.5 times faster than tyrosine. Hence, oceanic bacterioplankton as a community showed a clear preference for amino acids, particularly leucine, compared to amino sugars. The preferential uptake of amino acids to sugars challenges the concept of microbial nitrogen or carbon limitation in the open ocean.
Key Words: Heterotrophic bacterioplankton • organic nitrogen • bioavailability • bioassay • radiotracer
Communicating Editor: K. J. Flynn
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