Discovery of a SAR11 growth requirement for thiamin's pyrimidine precursor and its distribution in the Sargasso Sea |
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Authors: | Paul Carini Emily O Campbell Jeff Morré Sergio A Sa?udo-Wilhelmy J Cameron Thrash Samuel E Bennett Ben Temperton Tadhg Begley Stephen J Giovannoni |
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Institution: | 1.Department of Microbiology, Oregon State University, Corvallis, OR, USA;2.Department of Chemistry, Oregon State University, Corvallis, OR, USA;3.Department of Biological Sciences, Marine Environmental Biology, and Earth Science, University of Southern California, Los Angeles, CA, USA;4.Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis, OR, USA;5.Department of Chemistry, Texas A&M University, College Station, TX, USA |
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Abstract: | Vitamin traffic, the production of organic growth factors by some microbial community members and their use by other taxa, is being scrutinized as a potential explanation for the variation and highly connected behavior observed in ocean plankton by community network analysis. Thiamin (vitamin B1), a cofactor in many essential biochemical reactions that modify carbon–carbon bonds of organic compounds, is distributed in complex patterns at subpicomolar concentrations in the marine surface layer (0–300 m). Sequenced genomes from organisms belonging to the abundant and ubiquitous SAR11 clade of marine chemoheterotrophic bacteria contain genes coding for a complete thiamin biosynthetic pathway, except for thiC, encoding the 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP) synthase, which is required for de novo synthesis of thiamin''s pyrimidine moiety. Here we demonstrate that the SAR11 isolate ‘Candidatus Pelagibacter ubique'', strain HTCC1062, is auxotrophic for the thiamin precursor HMP, and cannot use exogenous thiamin for growth. In culture, strain HTCC1062 required 0.7 zeptomoles per cell (ca. 400 HMP molecules per cell). Measurements of dissolved HMP in the Sargasso Sea surface layer showed that HMP ranged from undetectable (detection limit: 2.4 pM) to 35.7 pM, with maximum concentrations coincident with the deep chlorophyll maximum. In culture, some marine cyanobacteria, microalgae and bacteria exuded HMP, and in the Western Sargasso Sea, HMP profiles changed between the morning and evening, suggesting a dynamic biological flux from producers to consumers. |
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Keywords: | vitamins thiamine B1 phytoplankton micronutrient auxotrophy |
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