Department of Marine Sciences, University of Georgia, Athens, GA, USA.
Department of Statistics, University of Georgia, Athens, GA, USA.
Environ Microbiol. 2018 Aug;20(8):3012-3030. doi: 10.1111/1462-2920.14344. Epub 2018 Jul 30.
Understanding which compounds comprising the complex and dynamic marine dissolved organic matter (DOM) pool are important in supporting heterotrophic bacterial production remains a major challenge. We eliminated sources of labile phytoplankton products, advected terrestrial material and photodegradation products to coastal microbial communities by enclosing water samples in situ for 24 h in the dark. Bacterial genes for which expression decreased between the beginning and end of the incubation and chemical formulae that were depleted over this same time frame were used as indicators of bioavailable compounds, an approach that avoids augmenting or modifying the natural DOM pool. Transport- and metabolism-related genes whose relative expression decreased implicated osmolytes, carboxylic acids, fatty acids, sugars and organic sulfur compounds as candidate bioreactive molecules. FT-ICR MS analysis of depleted molecular formulae implicated functional groups ~ 30-40 Da in size cleaved from semi-polar components of DOM as bioreactive components. Both gene expression and FT-ICR MS analyses indicated higher lability of compounds with sulfur and nitrogen heteroatoms. Untargeted methodologies able to integrate biological and chemical perspectives can be effective strategies for characterizing the labile microbial metabolites participating in carbon flux.
了解哪些化合物构成了复杂且动态的海洋溶解有机物（DOM）库，对于支持异养细菌的生产仍然是一个主要挑战。我们通过将水样在黑暗中现场封闭 24 小时，从而消除了易变的浮游植物产物、平流输入的陆地物质和光降解产物的来源，以适应沿海微生物群落。在孵育开始和结束之间表达减少的细菌基因和在此相同时间段内耗尽的化学公式被用作可生物利用化合物的指标，这种方法避免了对自然 DOM 库的补充或修饰。相对表达减少的运输和代谢相关基因表明，渗透调节剂、羧酸、脂肪酸、糖和有机硫化合物是候选生物反应性分子。对消耗的分子公式进行的 FT-ICR MS 分析表明，从 DOM 的半极性成分中切割下来的具有 30-40 Da 左右大小的功能基团是生物反应性成分。基因表达和 FT-ICR MS 分析都表明，含硫和氮杂原子的化合物的不稳定性更高。能够整合生物学和化学观点的非靶向方法可能是表征参与碳通量的微生物代谢物的有效策略。
