We have previously described that laboratory strains of Ustilago maydis, a fungal pathogen of maize and its ancestor teosinte, harbor an intracellular bacterium that enables the fungus to fix nitrogen. However, it is not clear whether other strains isolated from nature also harbor endosymbiotic bacteria, and whether these fix nitrogen for its host. In the present study, we isolated U. maydis strains from naturally infected maize. All the isolated strains harbored intracellular bacteria as determined by PCR amplification of the 16S rRNA gene, and some of them showed capacity to fix nitrogen. That these are truly bacterial endosymbionts were shown by the fact that, after thorough treatments with CuSO4 followed by serial incubations with antibiotics, the aforementioned bacterial gene was still amplified in treated fungi. In all, these data support the notion that U. maydis-bacterium endosymbiosis is a general phenomenon in this species.

中文翻译：

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Ustilago maydis-细菌内共生在自然感染的玉米植株中的广泛分布

我们之前已经描述过黑粉病菌（玉米及其祖先 teosinte 的真菌病原体）的实验室菌株含有一种细胞内细菌，使真菌能够固氮。然而，尚不清楚从自然界分离的其他菌株是否也含有内共生细菌，以及这些细菌是否为其宿主固氮。在本研究中，我们从自然感染的玉米中分离了 U. maydis 菌株。通过16S rRNA基因的PCR扩增确定，所有分离的菌株都含有胞内细菌，其中一些菌株显示出固氮能力。这些是真正的细菌内共生体的事实表明，在用 CuSO4 彻底处理，然后用抗生素连续孵育后，上述细菌基因仍然在处理过的真菌中扩增。在所有，