Journal ArticleThe cycling of glycine betaine and homarine in marine microbial communities: Quantitative flux measurements and the role of competitive uptake inhibitionSacks, Joshua S [School of Oceanography University of Washington Seattle Washington USA] (ORCID:0000000285130589); Carlson, Laura T [School of Oceanography University of Washington Seattle Washington USA] (ORCID:000900059453738X); Finch, Anna H [Department of Earth System Science Stanford University Stanford California USA] (ORCID:0009000721607177); Ferrer‐González, Frank X [School of Oceanography University of Washington Seattle Washington USA] (ORCID:0000000305705168); Boysen, Angela K [Department of Chemistry Pacific Lutheran University Tacoma Washington USA] (ORCID:000000018193630X); Heal, Katherine R [Pacific Northwest National Laboratories Richland Washington USA] (ORCID:0000000245041039); Karl, David M [Department of Oceanography University of Hawai'i at Mānoa Honolulu Hawaii USA] (ORCID:0000000266606721); White, Angelicque E [Department of Oceanography University of Hawai'i at Mānoa Honolulu Hawaii USA] (ORCID:0000000209387948); Sosa, Oscar A [Department of Biology University of Puget Sound Tacoma Washington USA] (ORCID:0000000342359962); Ingalls, Anitra E [School of Oceanography University of Washington Seattle Washington USA] (ORCID:0000000319537329)<title>Abstract</title> <p>The flux of carbon through the labile dissolved organic matter (DOM) pool supports marine microbial communities and represents the fate of approximately half of marine net primary production (NPP). However, the behavior of individual chemical structures that make up labile DOM remain largely unknown. We performed 12 uptake kinetics and two uptake competition experiments on the abundant betaine osmolytes glycine betaine (GBT) and homarine. Combining uptake kinetics with dissolved metabolite measurements, we quantified fluxes through the DOM pool. Fluxes were correlated with particulate concentrations and ranged from 0.53 to 41 and 0.003 to 0.54 nmol L⁻¹ d⁻¹for GBT and homarine, respectively, equivalent to up to 1.2% of NPP. Turnover times of dissolved GBT and homarine ranged from 1 to 57 d. Betaines and sulfoniums such as dimethylsulfoniopropionate competitively inhibited homarine uptake. Our results quantify GBT and homarine cycling and suggest an important role for uptake competition in regulating dissolved metabolite concentrations and fluxes.</p>ASLO2026-01-0110654875Limnology and Oceanography Letters1112378-2242https://doi.org/10.1002/lol2.700692125886National Science Foundation