title: Sample dilution and bacterial community composition influence empirical leucine-to-carbon conversion factors in surface waters of the world's oceans.
abstract: The transformation of leucine incorporation rates to prokaryotic carbon production rates requires the use of either theoretical or empirically determined conversion factors. Empirical leucine-to-carbon conversion factors (eCFs) vary widely across environments, and little is known about their potential controlling factors. We conducted 10 surface seawater manipulation experiments across the world's oceans, where the growth of the natural prokaryotic assemblages was promoted by filtration (i.e., removal of grazers [F treatment]) or filtration combined with dilution (i.e., also relieving resource competition [FD treatment]). The impact of sunlight exposure was also evaluated in the FD treatments, and we did not find a significant effect on the eCFs. The eCFs varied from 0.09 to 1.47 kg C mol Leu(-1) and were significantly lower in the FD than in the F samples. Also, changes in bacterial community composition during the incubations, as assessed by automated ribosomal intergenic spacer analysis (ARISA), were more pronounced in the FD than in the F treatments, compared to unmanipulated controls. Thus, we discourage the common procedure of diluting samples (in addition to filtration) for eCF determination. The eCFs in the filtered treatment were negatively correlated with the initial chlorophyll a concentration, picocyanobacterial abundance (mostly Prochlorococcus), and the percentage of heterotrophic prokaryotes with high nucleic acid content (%HNA). The latter two variables explained 80% of the eCF variability in the F treatment, supporting the view that both Prochlorococcus and HNA prokaryotes incorporate leucine in substantial amounts, although this results in relatively low carbon production rates in the oligotrophic ocean.
authors.affiliation: Universidade de Vigo, Vigo, Spain teira@uvigo.es.
authors.forename: Eva
authors.initials: E
authors.lastname: Teira
authors.affiliation: Universidade de Vigo, Vigo, Spain.
authors.forename: Víctor
authors.initials: V
authors.lastname: Hernando-Morales
authors.affiliation: Institut de Ciències del Mar, CSIC, Barcelona, Spain.
authors.forename: Francisco M
authors.initials: FM
authors.lastname: Cornejo-Castillo
authors.affiliation: AZTI, Sukarrieta, Spain Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Xixón, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Alonso-Sáez
authors.affiliation: Department of Hydrobiology, Federal University of São Carlos, São Carlos, São Paulo, Brazil.
authors.forename: Hugo
authors.initials: H
authors.lastname: Sarmento
authors.affiliation: Instituto Español de Oceanografía, Centro Oceanográfico de A Coruña, A Coruña, Spain.
authors.forename: Joaquín
authors.initials: J
authors.lastname: Valencia-Vila
authors.affiliation: Universidad de Granada, Granada, Spain.
authors.forename: Teresa
authors.initials: T
authors.lastname: Serrano Catalá
authors.affiliation: Universidade de Vigo, Vigo, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Hernández-Ruiz
authors.affiliation: Instituto Español de Oceanografía, Centro Oceanográfico de A Coruña, A Coruña, Spain.
authors.forename: Marta M
authors.initials: MM
authors.lastname: Varela
authors.affiliation: Institut de Ciències del Mar, CSIC, Barcelona, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Ferrera
authors.affiliation: Red Sea Research Center, Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Xixón, Spain.
authors.forename: Xosé Anxelu
authors.initials: XA
authors.lastname: Gutiérrez Morán
authors.affiliation: Institut de Ciències del Mar, CSIC, Barcelona, Spain.
authors.forename: Josep M
authors.initials: JM
authors.lastname: Gasol
mesh_terms: D001419:Bacteria / Q000302:isolation & purification; D001431:Bacteriological Techniques / Q000379:methods*; D002244:Carbon / Q000378:metabolism*; D004783:Environmental Microbiology; D007930:Leucine / Q000378:metabolism*; D064307:Microbiota; D009792:Oceans and Seas; D012623:Seawater / Q000382:microbiology*; D014329:Tropical Climate
chemical_list: D002244:Carbon; D007930:Leucine