Biomass production and assimilation of dissolved organic matter by SAR11 bacteria in the Northwest Altantic

• Main Authors: Rex R. Malmstrom, Matthew T. Cottrell, Hila Elifantz, David L. Kirchman
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2005
• Subjects: Northwest Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.540.526; http://hahana.soest.hawaii.edu/agouroninstitutecourse/Malmstrom AEM SAR11 2005.pdf

Members of the SAR11 clade often dominate the composition of marine microbial communities, yet their contribution to biomass production and the flux of dissolved organic matter (DOM) is unclear. In addition, little is known about the specific components of the DOM pool utilized by SAR11 bacteria. To better under-stand the role of SAR11 bacteria in the flux of DOM, we examined the assimilation of leucine (a measure of biomass production), as well as free amino acids, protein, and glucose, by SAR11 bacteria in the Northwest Atlantic Ocean. We found that when SAR11 bacteria were>25 % of total prokaryotes, they accounted for about 30 to 50 % of leucine incorporation, suggesting that SAR11 bacteria were major contributors to bacterial biomass production and the DOM flux. Specific growth rates of SAR11 bacteria either equaled or exceeded growth rates for the total prokaryotic community. In addition, SAR11 bacteria were typically responsible for a greater portion of amino acid assimilation (34 to 61%) and glucose assimilation (45 to 57%) than of protein assimilation (<34%). These data suggest that SAR11 bacteria do not utilize various components of the DOM pool equally and may be more important to the flux of low-molecular-weight monomers than to that of high-molecular-weight polymers. The SAR11 clade is one of the most abundant bacterial phylogenetic groups in the ocean. About 25 % of the 16S rRNA