Highly efficient detoxification of dinitrotoluene through overexpressing
bacterial nitroreductase in switchgrass
Dinitrotoluene (DNT) has been extensively used in manufacturing
munitions, polyurethane foams, and other important chemical products.
However, it is highly toxic and mutagenic to most organisms. Here, we
synthesized a codon optimized bacterial nitroreductase gene, NfsI, for
plant expression. The kinetic analysis indicates that the recombinant
NfsI can detoxify both 2,4-DNT and its sulfonate (DNTS), while it has a
97.6-fold higher catalytic efficiency for 2,4-DNT than DNTS.
Furthermore, we overexpressed NfsI in switchgrass (Panicum virgatum L.),
which is a multiple purpose crop used for fodder and biofuel production
as well as phytoremediation. The 2,4-DNT treatment inhibited root
elongation of wild type switchgrass plants and promoted reactive oxygen
species (ROS) accumulation in roots. In contrast, overexpression of NfsI
in switchgrass significantly alleviated 2,4-DNT-induced root growth
inhibition and ROS overproduction. Thus, the NfsI overexpressing
transgenic switchgrass plant removed 94.1% 2,4-DNT after 6 days, whose
efficiency was 1.7-fold higher than control plants. Moreover, the
comparative transcriptome analysis suggests that 22.9% of
differentially expressed genes induced by 2,4-DNT may participate in
NfsI-mediated 2,4-DNT detoxification in switchgrass. Our work sheds
light on the function of NfsI during DNT phytoremediation for the first
time, revealing the application potential of switchgrass plants
engineered with NfsI.