Mixotrophy, the combination of heterotrophic and autotrophic nutrition modes, is emerging as the rule rather than the exception in marine photosynthetic plankton. Trichodesmium, a prominent diazotroph ubiquitous in the (sub)tropical oceans, is generally considered to obtain energy via autotrophy. While the ability of Trichodesmium to use dissolved organic phosphorus when deprived of inorganic phosphorus sources is well known, the extent to which this important cyanobacterium may benefit from other dissolved organic matter (DOM) resources is unknown. Here we provide evidence of carbon-, nitrogen- and phosphorus-rich DOM molecules enhancing N2 fixation rates and nifH gene expression in natural Trichodesmium colonies collected at two stations in the western tropical South Pacific. Sampling at a third station located in the oligotrophic South Pacific Gyre revealed no Trichodesmium but showed presence of UCYN-B, although no nifH expression was detected. Our results suggest that Trichodesmium behaves mixotrophically in response to certain environmental conditions, providing them with metabolic plasticity and adding up to the view that mixotrophy is widespread among marine microbes.

中文翻译：

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溶解的有机物刺激了Trichodesmium中的N2固定和nifH基因表达。

混合营养，是异养营养模式和自养营养模式的结合，在海洋光合作用浮游生物中已成为常规而非常规。在（亚）热带海洋中普遍存在的重要的重氮营养体，Trichodesmium通常被认为是通过自养获得能量的。虽然众所周知，当去除无机磷源时，毛线虫利用溶解的有机磷的能力，但这种重要的蓝细菌可从其他溶解的有机物（DOM）资源中受益的程度尚不清楚。在这里，我们提供了富含碳，氮和磷的DOM分子的证据，这些分子增强了在南热带西部两个站点收集的天然毛线虫菌落中的N2固定率和nifH基因表达。在贫营养型南太平洋涡旋的第三站采样表明，虽然未检测到nifH表达，但未发现Trichodesmium，但显示了UCYN-B。我们的结果表明，毛线虫在某些环境条件下表现出混合营养性，为它们提供了代谢可塑性，并加在一起认为混合营养在海洋微生物中很普遍。