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SAR11 bacteria have a high affinity and multifunctional glycine betaine transporter
Author(s) -
Noell Stephen E.,
Giovani Stephen J.
Publication year - 2019
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/1462-2920.14649
Subject(s) - biology , periplasmic space , betaine , biochemistry , alphaproteobacteria , glycine , synechococcus , bacteria , amino acid , escherichia coli , cyanobacteria , genetics , 16s ribosomal rna , gene
Summary Marine bacterioplankton face stiff competition for limited nutrient resources. SAR11, a ubiquitous clade of very small and highly abundant Alphaproteobacteria , are known to devote much of their energy to synthesizing ATP‐binding cassette periplasmic proteins that bind substrates. We hypothesized that their small size and relatively large periplasmic space might enable them to outcompete other bacterioplankton for nutrients. Using uptake experiments with 14 C‐glycine betaine, we discovered that two strains of SAR11, Candidatus Pelagibacter sp. HTCC7211 and Cand . P. ubique HTCC1062, have extraordinarily high affinity for glycine betaine (GBT), with half‐saturation ( K s ) values around 1 nM and specific affinity values between 8 and 14 L mg cell −1 h −1 . Competitive inhibition studies indicated that the GBT transporters in these strains are multifunctional, transporting multiple substrates in addition to GBT. Both strains could use most of the transported compounds for metabolism and ATP production. Our findings indicate that Pelagibacter cells are primarily responsible for the high affinity and multifunctional GBT uptake systems observed in seawater. Maximization of whole‐cell affinities may enable these organisms to compete effectively for nutrients during periods when the gross transport capacity of the heterotrophic plankton community exceeds the supply, depressing ambient concentrations.