Fernández Helga, Prandoni Nicolás, Fernández-Pascual Mercedes, Fajardo Susana, Morcillo César, Díaz Eduardo, Carmona Manuel
Department of Environmental Biology, Centro de Investigaciones Biológicas-CSIC, Madrid, Spain.
Plant Protection Department, Instituto de Ciencias Agrarias-CSIC, Madrid, Spain.
PLoS One. 2014 Oct 23;9(10):e110771. doi: 10.1371/journal.pone.0110771. eCollection 2014.
Endophytic bacteria that have plant growth promoting traits are of great interest in green biotechnology. The previous thought that the Azoarcus genus comprises bacteria that fit into one of two major eco-physiological groups, either free-living anaerobic biodegraders of aromatic compounds or obligate endophytes unable to degrade aromatics under anaerobic conditions, is revisited here.
METHODOLOGY/PRINCIPAL FINDINGS: Light, confocal and electron microscopy reveal that Azoarcus sp. CIB, a facultative anaerobe β-proteobacterium able to degrade aromatic hydrocarbons under anoxic conditions, is also able to colonize the intercellular spaces of the rice roots. In addition, the strain CIB displays plant growth promoting traits such nitrogen fixation, uptake of insoluble phosphorus and production of indoleacetic acid. Therefore, this work demonstrates by the first time that a free-living bacterium able to degrade aromatic compounds under aerobic and anoxic conditions can share also an endophytic lifestyle. The phylogenetic analyses based on the 16S rDNA and nifH genes confirmed that obligate endophytes of the Azoarcus genus and facultative endophytes, such as Azoarcus sp. CIB, locate into different evolutionary branches.
CONCLUSIONS/SIGNIFICANCE: This is the first report of a bacterium, Azoarcus sp. CIB, able to degrade anaerobically a significant number of aromatic compounds, some of them of great environmental concern, and to colonize the rice as a facultative endophyte. Thus, Azoarcus sp. CIB becomes a suitable candidate for a more sustainable agricultural practice and phytoremediation technology.
具有促进植物生长特性的内生细菌在绿色生物技术中备受关注。以往认为固氮弧菌属细菌可分为两个主要生态生理类群之一，即自由生活的芳香族化合物厌氧降解菌或在厌氧条件下无法降解芳香族化合物的专性内生菌，本文对此观点进行了重新审视。
方法/主要发现：光学显微镜、共聚焦显微镜和电子显微镜观察表明，固氮弧菌属菌株CIB是一种兼性厌氧β-变形菌，能够在缺氧条件下降解芳香烃，同时也能够定殖于水稻根的细胞间隙。此外，菌株CIB还表现出促进植物生长的特性，如固氮、吸收难溶性磷和产生吲哚乙酸。因此，这项工作首次证明了一种在好氧和缺氧条件下都能降解芳香族化合物的自由生活细菌也可以具有内生生活方式。基于16S rDNA和nifH基因的系统发育分析证实，固氮弧菌属的专性内生菌和兼性内生菌，如固氮弧菌属菌株CIB，位于不同的进化分支。
结论/意义：这是关于固氮弧菌属菌株CIB的首次报道，该菌株能够在厌氧条件下降解大量芳香族化合物，其中一些对环境具有重大影响，并且能够作为兼性内生菌定殖于水稻中。因此，固氮弧菌属菌株CIB成为更可持续农业实践和植物修复技术的合适候选者。
