Novel small multidrug resistance protein Tmt endows the Escherichia coli with triphenylmethane dyes bioremediation capability

Abstract Dye contamination in printing and dyeing wastewater has long been a major concern due to its serious impact on both the environment and human health. Recently, biological processes have emerged as a promising approach for the treatment of dye pollutants. In this study, a triphenylmethane transporter gene (tmt) was identified from 6 distinct clones screening from a metagenomics library of the printing and dyeing wastewater treatment syste. Escherichia coli expressing tmt revealed 98.1% decolorization efficiency of triphenylmethane dye malachite green within 24 h under shaking culture condition. The tolerance to malachite green was improved over eight-fold in the Tmt strain compared of the none-Tmt expressed strain. Similarly, the tolerance of Tmt strain to other triphenylmethane dyes like crystal violet and brilliant green, was improved by at least four-fold. Site-directed mutations, including A75G, A75S and V100G, were found to reinforce the tolerance of malachite green, and double mutations of these even further improve the tolerance. Therefore, the tmt has been demonstrated to be a specific efflux pump for triphenylmethane dyes, particularly the malachite green. By actively pumping out toxic triphenylmethane dyes, it significantly extends the cells tolerance in a triphenylmethane dye–rich environment, which may provide a promising strategy for bioremediation of triphenylmethane dye pollutants in the environments.