Goto Shuji, Tada Yuya, Suzuki Koji, Yamashita Youhei
Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan.
National Institute for Minamata Disease, Minamata, Japan.
Front Microbiol. 2020 Oct 15;11:584419. doi: 10.3389/fmicb.2020.584419. eCollection 2020.
A large part of marine dissolved organic matter (DOM) is considered to be recalcitrant DOM (RDOM) produced by marine bacteria. However, it is still unclear whether differences in bacterial species and/or physiology control the efficiency of RDOM production. Here, batch culture experiments with glucose as the sole carbon source were carried out using three model marine bacterial strains, namely, (Alt), (Vib), and (Pha). Dissolved organic carbon (DOC) concentrations drastically decreased during the exponential growth phases of these bacteria due to the consumption of glucose. The efficiency of bacterial DOC production at the end of incubation was largely different among the strains and was higher for Vib (20%) than for the other two strains (Alt, 4%; Pha, 6%). All strains produced fluorescent DOM (FDOM), including humic-like FDOM which is considered as recalcitrant component in the ocean, even though the composition of bacterial FDOM was also different among the strains. The efficiency of humic-like FDOM production during the exponential growth phase was different among the bacterial strains; that is, Pha produced humic-like FDOM efficiently compared with the other two species. The efficiency of humic-like FDOM production with mineralization of organic matter was lower during the exponential growth phase than during the stationary phase of Alt and Pha. Four processes for the production of bacterially derived recalcitrant humic-like FDOM are suggested from this study: (1) production during active growing (in all strains), (2) production with the reutilization of bacterial DOM (Alt), (3) production with the consumption of cellular materials (Pha), and (4) release from lysis (Vib). Our results suggest that bacterial species and physiology can regulate RDOM production and accumulation in the ocean.
大部分海洋溶解有机物（DOM）被认为是由海洋细菌产生的难降解DOM（RDOM）。然而，细菌种类和/或生理特性的差异是否控制RDOM的产生效率仍不清楚。在此，以葡萄糖为唯一碳源，使用三种典型海洋细菌菌株进行了分批培养实验，即（Alt）、（Vib）和（Pha）。由于葡萄糖的消耗，在这些细菌的指数生长阶段，溶解有机碳（DOC）浓度急剧下降。培养结束时，细菌DOC产生效率在菌株间有很大差异，Vib的效率更高（20%），高于其他两种菌株（Alt，4%；Pha，6%）。所有菌株都产生了荧光DOM（FDOM），包括被认为是海洋中难降解成分的类腐殖质FDOM，尽管细菌FDOM的组成在菌株间也有所不同。在指数生长阶段，类腐殖质FDOM的产生效率在细菌菌株间存在差异；也就是说，与其他两个物种相比，Pha能高效产生类腐殖质FDOM。在指数生长阶段，类腐殖质FDOM随有机物矿化的产生效率低于Alt和Pha的稳定期。本研究提出了细菌来源的难降解类腐殖质FDOM产生的四个过程：（1）活跃生长期间产生（所有菌株），（2）细菌DOM再利用产生（Alt），（3）细胞物质消耗产生（Pha），以及（4）细胞裂解释放（Vib）。我们的结果表明，细菌种类和生理特性可以调节海洋中RDOM的产生和积累。
