Kellogg Natalie A, Fuchsman Clara A, Carlson Laura T, Morris Robert M, Ingalls Anitra E, Rocap Gabrielle
School of Oceanography, University of Washington, Seattle, WA, USA.
University of Maryland Center for Environmental Science, Horn Point Laboratory, Cambridge, Maryland, USA.
Environ Microbiol. 2025 Aug;27(8):e70119. doi: 10.1111/1462-2920.70119.
Oxygen deficient zones (ODZs) are subsurface marine systems that harbour distinct microbial communities, including populations of the picocyanobacteria Prochlorococcus that can form a secondary chlorophyll maximum (SCM), and low-oxygen tolerant strains of the globally abundant heterotroph Pelagibacter (SAR11). Yet, the small labile molecules (metabolites) responsible for maintaining these ODZ communities are unknown. Here, we compared the metabolome of an ODZ to that of an oxygenated site by quantifying 87 metabolites across depth profiles in the eastern tropical North Pacific ODZ and the oxygenated waters of the North Pacific Gyre. Metabolomes were largely consistent between anoxic and oxic water columns. However, the osmolyte glycine betaine (GBT) was enriched in the oxycline and SCM of the ETNP, comprising as much as 1.2% of particulate organic carbon. Transcriptomes revealed two active GBT production pathways, glycine methylation (SDMT/bsmB) expressed by Prochlorococcus and choline oxidation (betB) expressed by Gammaproteobacteria. GBT consumption through demethylation involved diverse microbial taxa, with SAR11 contributing nearly half of the transcripts for the initial step of GBT demethylation (BHMT), which is predicted to convert GBT and homocysteine into dimethylglycine and methionine, a compound SAR11 cannot otherwise produce. Thus, GBT connects the metabolisms of the dominant phototroph and heterotroph in the oceans.
缺氧区（ODZs）是海洋次表层系统，其中存在独特的微生物群落，包括能够形成叶绿素次极大值（SCM）的聚球藻原绿球藻种群，以及全球丰富的异养细菌嗜甲基菌（SAR11）的耐低氧菌株。然而，维持这些缺氧区群落的不稳定小分子（代谢物）尚不清楚。在这里，我们通过量化东热带北太平洋缺氧区和北太平洋环流含氧水域深度剖面中的87种代谢物，比较了缺氧区与含氧区域的代谢组。缺氧水柱和含氧水柱之间的代谢组在很大程度上是一致的。然而，渗透调节物质甘氨酸甜菜碱（GBT）在东热带北太平洋的氧跃层和叶绿素次极大值层中富集，占颗粒有机碳的1.2%。转录组揭示了两条活跃的GBT产生途径，即原绿球藻表达的甘氨酸甲基化（SDMT/bsmB）和γ-变形菌表达的胆碱氧化（betB）。通过去甲基化消耗GBT涉及多种微生物类群，SAR11贡献了GBT去甲基化（BHMT）第一步近一半的转录本，预计该步骤将GBT和同型半胱氨酸转化为二甲基甘氨酸和甲硫氨酸，而甲硫氨酸是SAR11无法通过其他方式产生的化合物。因此，GBT连接了海洋中主要光合生物和异养生物的代谢。
