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Applied and Environmental Microbiology, May 2009, p. 3216-3221, Vol. 75, No. 10
0099-2240/09/$08.00+0     doi:10.1128/AEM.01570-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Empirical Leucine-to-Carbon Conversion Factors for Estimating Heterotrophic Bacterial Production: Seasonality and Predictability in a Temperate Coastal Ecosystem{triangledown}

Alejandra Calvo-Díaz1* and Xosé Anxelu G. Morán1,2

Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Camín de L'Arbeyal, s/n, E-33212 Xixón, Spain,1 The Ecosystems Center, MBL, 7 MBL Street, Woods Hole, Massachusetts 02543-10152

Received 10 July 2008/ Accepted 16 March 2009

Leucine-to-carbon conversion factors (CFs) are needed for converting substrate incorporation into biomass production of heterotrophic bacteria. During 2006 we performed 20 dilution experiments for determining the spatiotemporal variability of empirical CFs in temperate Atlantic coastal waters. Values (0.49 to 1.92 kg C mol Leu–1) showed maxima in autumn to early winter and minima in summer. Spatially averaged CFs were significantly negatively correlated with in situ leucine incorporation rates (r = –0.91) and positively correlated with phosphate concentrations (r = 0.76). These relationships, together with a strong positive covariation between cell-specific leucine incorporation rates and carbon contents (r = 0.85), were interpreted as a strategy to maximize survival through protein synthesis and low growth rates under nutrient limitation (low CFs) until favorable conditions stimulate cell division relative to protein synthesis (high CFs). A multiple regression with in situ leucine incorporation rates and cellular carbon contents explained 96% of CF variance in our ecosystem, suggesting their potential prediction from more easily measurable routine variables. The use of the theoretical CF of 1.55 kg C mol Leu–1 would have resulted in a serious overestimation (73%) of annual bacterial production rates. Our results emphasize the need for considering the temporal scale in CFs for bacterial production studies.

* Corresponding author. Mailing address: Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Camín de L'Arbeyal, s/n, E-33212 Xixón, Spain. Phone: 34 985308672. Fax: 34 985326277. E-mail: a.calvodiaz{at}gi.ieo.es

{triangledown} Published ahead of print on 20 March 2009.

Applied and Environmental Microbiology, May 2009, p. 3216-3221, Vol. 75, No. 10
0099-2240/09/$08.00+0     doi:10.1128/AEM.01570-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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