Abstract
Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a widely used explosive and a major soil and groundwater contaminant. Organisms such as Gordonia sp. KTR9, capable of degrading RDX and using it as an N source, may prove useful for bioremediation of contaminated sites. XplA is a cytochrome P450 monooxygenase responsible for RDX degradation. Expression of xplA in KTR9 was not induced by RDX but was strongly induced (50-fold) during N-limited growth. When glnR, encoding a regulatory protein affecting N assimilation in diverse Actinobacteria, was deleted from KTR9, the bacterium lost the ability to use nitrate, nitrite, and RDX as N sources. Deletion of glnR also abolished the inhibition of xplA expression by nitrite. Our results confirm the essential role of GlnR in regulating assimilation of nitrite, but there was no evidence for a direct role of GlnR in regulating XplA expression. Rather, the general availability of nitrogen repressed XplA expression. We conclude that the inability of the glnR mutant to use RDX as an N source was due to its inability to assimilate nitrite, an intermediate in the assimilation of nitrogen from RDX. Regulation of XplA does not seem adaptive for KTR9, but it is important for RDX bioremediation with KTR9 or similar bacteria.
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Acknowledgments
This research was funded in part through grants from Genome BC, the Strategic Environmental Research and Development Program (Project ER-1609), and the US Army Corps of Engineers Environmental Quality Program. Views, opinions, and/or findings contained herein are those of the authors and should not be construed as an official Department of the Army position or decision unless so designated by other official documentation. We thank Christine Florizone for guidance in chemical analyses.
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Zhu, SH., Reuther, J., Liu, J. et al. The essential role of nitrogen limitation in expression of xplA and degradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in Gordonia sp. strain KTR9. Appl Microbiol Biotechnol 99, 459–467 (2015). https://doi.org/10.1007/s00253-014-6013-z
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DOI: https://doi.org/10.1007/s00253-014-6013-z