Pontiller Benjamin, Martínez-García Sandra, Lundin Daniel, Pinhassi Jarone
Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University, Kalmar, Sweden.
Departamento de Ecoloxía e Bioloxía Animal, Universidade de Vigo, Vigo, Spain.
Front Microbiol. 2020 Sep 25;11:588778. doi: 10.3389/fmicb.2020.588778. eCollection 2020.
Bacteria play a key role in the planetary carbon cycle partly because they rapidly assimilate labile dissolved organic matter (DOM) in the ocean. However, knowledge of the molecular mechanisms at work when bacterioplankton metabolize distinct components of the DOM pool is still limited. We, therefore, conducted seawater culture enrichment experiments with ecologically relevant DOM, combining both polymer and monomer model compounds for distinct compound classes. This included carbohydrates (polysaccharides vs. monosaccharides), proteins (polypeptides vs. amino acids), and nucleic acids (DNA vs. nucleotides). We noted pronounced changes in bacterial growth, activity, and transcription related to DOM characteristics. Transcriptional responses differed between compound classes, with distinct gene sets ("core genes") distinguishing carbohydrates, proteins, and nucleic acids. Moreover, we found a strong divergence in functional transcription at the level of particular monomers and polymers (i.e., the condensation state), primarily in the carbohydrates and protein compound classes. These specific responses included a variety of cellular and metabolic processes that were mediated by distinct bacterial taxa, suggesting pronounced functional partitioning of organic matter. Collectively, our findings show that two important facets of DOM, compound class and condensation state, shape bacterial gene expression, and ultimately select for distinct bacterial (functional) groups. This emphasizes the interdependency of marine bacteria and labile carbon compounds for regulating the transformation of DOM in surface waters.
细菌在全球碳循环中发挥着关键作用，部分原因是它们能迅速同化海洋中不稳定的溶解有机物（DOM）。然而，关于浮游细菌代谢DOM库中不同成分时所涉及的分子机制的了解仍然有限。因此，我们用与生态相关的DOM进行了海水培养富集实验，将聚合物和单体模型化合物结合用于不同的化合物类别。这包括碳水化合物（多糖与单糖）、蛋白质（多肽与氨基酸）以及核酸（DNA与核苷酸）。我们注意到与DOM特性相关的细菌生长、活性和转录有明显变化。不同化合物类别之间的转录反应有所不同，有不同的基因集（“核心基因”）区分碳水化合物、蛋白质和核酸。此外，我们发现在特定单体和聚合物水平（即缩合状态）上功能转录存在很大差异，主要体现在碳水化合物和蛋白质化合物类别中。这些特定反应包括由不同细菌类群介导的各种细胞和代谢过程，表明有机物存在明显的功能划分。总体而言，我们的研究结果表明，DOM的两个重要方面，即化合物类别和缩合状态，塑造了细菌的基因表达，并最终选择了不同的细菌（功能）群体。这强调了海洋细菌与不稳定碳化合物在调节表层水体中DOM转化方面的相互依存关系。
