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Relationships between coastal bacterioplankton growth rates and biomass production: comparison of leucine and thymidine uptake with single-cell physiological characteristics.
MedLine Citation:
PMID:  21120654     Owner:  NLM     Status:  In-Data-Review    
Specific growth rates of heterotrophic bacterioplankton have been frequently estimated from in situ bacterial production (BP) to biomass (BB) ratios, using a series of assumptions that may result in serious discrepancies with values obtained from predator-free cultures. Here, we used both types of approaches together with a comprehensive assessment of single-cell physiological characteristics (membrane integrity, nucleic acid content, and active respiration) of coastal bacterioplankton during a complete annual cycle (February 2007-January 2008) in the southern Bay of Biscay off Xixón, Spain. Both leucine and thymidine incorporation rates were used in conjunction with empirical tracer to carbon or cells conversion factors (eCFs) to accurately derive BP. Leu and TdR incorporation rates covaried year-round, as did the corresponding eCFs at 0 and 50 m depth. eCFs peaked in autumn, with mean annual values close to the theoretical ones (3.4 kg C mol Leu(-1) and 2.0 × 10(18) cells mol TdR(-1)). Bacterial abundance (0.2-1.5 × 10(6) cells L(-1)) showed a bimodal distribution with maxima in May and October and minima in March. Live (membrane-intact) cells dominated year-round (79-97%), with high nucleic acid cells (42-88%) and actively respiring bacteria (CTC+, 1-16%) showing distinct surface maxima in April and July, respectively. BB (557-1,558 mg C m(-2)) and BP (7-139 mg C m(-2) day(-1)) presented two distinct peaks in spring and autumn, both of similar size due to a strong upwelling event observed in September. Specific growth rates (0.35-3.8 day(-1)) were one order of magnitude higher in predator-free incubations than bacterial turnover rates derived from integrated BP:BB ratios (0.01-0.16 and 0.01-0.09 day(-1), for Leu and TdR, respectively) and were not correlated, probably due to a significant contribution of low activity cells to total standing stocks. The Leu:TdR molar ratio averaged for the water column (6.6-25.5) decreased significantly with higher integrated BB, indicating that low standing stocks tend to present unbalanced growth. Discrepancies about the true magnitude of specific growth rates must be solved before fully appreciating the role of bacteria in the ocean carbon cycle.
Leticia Franco-Vidal; Xosé Anxelu G Morán
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Publication Detail:
Type:  Journal Article     Date:  2010-12-01
Journal Detail:
Title:  Microbial ecology     Volume:  61     ISSN:  1432-184X     ISO Abbreviation:  Microb. Ecol.     Publication Date:  2011 Feb 
Date Detail:
Created Date:  2011-02-11     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  7500663     Medline TA:  Microb Ecol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  328-41     Citation Subset:  IM    
Centro Oceanográfico de Xixón, Instituto Español de Oceanografía, Camín de L'Arbeyal, s/n, 33212, Xixón, Asturies, Spain.
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