Transformation of the explosive RDX by Gordonia sp. strain KTR9: implications for bioaugmentation.

Hexahydro-1,3,5-trinitro-1,3,5,-triazine (RDX) is a cyclic nitramine explosive used in various military and commercial activities which has resulted in contamination of soil and groundwater. Comparative analysis of gene induction patterns in RDX-degrading strain Gordonia sp. KTR9 revealed a significant overlap between the transcriptomes of cells grown on RDX as a sole nitrogen source with those starved for nitrogen under aerobic growth conditions. Genes involved in nitrogen transport, nitrogen assimilation and RDX degradation were common to both comparisons. When glnR, encoding a regulatory protein affecting N assimilation, was deleted from KTR9, the bacterium lost the ability to use nitrate, nitrite, and RDX as nitrogen sources. Additional transcriptome studies comparing the glnR KTR9 deletion mutant with the wild-type strain grown under excess vs. limited nitrogen demonstrated that the glnR mutant was impaired in up-regulation of key genes involved in nitrogen transport, nitrogen assimilation, and RDX degradation. The essential role of GlnR in regulating nitrite assimilation was confirmed by measuring consumption of various nitrogen sources and relative expression of xplA in time-series cell suspension studies comparing wild-type vs. glnR KTR9 strains. There was no evidence for a direct role of GlnR in regulating xplA expression, but rather the general availability of nitrogen repressed xplA expression. The inability of the glnR mutant to metabolize RDX as a nitrogen source is the result of its inability to assimilate nitrite from RDX. Currently, these insights are being applied at an explosives-contaminated groundwater site whereby an in situ bioaugmentation treatment strategy with strain KTR9 is being assessed.