Engineering Tobacco to Remove Mercury from Polluted Soil

Abstract

Tobacco is an ideal plant for modification to remove mercury from soil. Although several transgenic tobacco strains have been developed, they either release elemental mercury directly into the air or are only capable of accumulating small quantities of mercury. In this study, we constructed two transgenic tobacco lines: Ntk-7 (a tobacco plant transformed with merT-merP-merB1-merB2-ppk) and Ntp-36 (tobacco transformed with merT-merP-merB1-merB2-pcs1). The genes merT, merP, merB1, and merB2 were obtained from the well-known mercury-resistant bacterium Pseudomonas K-62. Ppk is a gene that encodes polyphosphate kinase, a key enzyme for synthesizing polyphosphate in Enterobacter aerogenes. Pcs1 is a tobacco gene that encodes phytochelatin synthase, which is the key enzyme for phytochelatin synthesis. The genes were linked with LP4/2A, a sequence that encodes a well-known linker peptide. The results demonstrate that all foreign genes can be abundantly expressed. The mercury resistance of Ntk-7 and Ntp-36 was much higher than that of the wild type whether tested with organic mercury or with mercuric ions. The transformed plants can accumulate significantly more mercury than the wild type, and Ntp-36 can accumulate more mercury from soil than Ntk-7. In mercury-polluted soil, the mercury content in Ntp-36's root can reach up to 251 μg/g. This is the first report to indicate that engineered tobacco can not only accumulate mercury from soil but also retain this mercury within the plant. Ntp-36 has good prospects for application in bioremediation for mercury pollution.

Polyphosphate in Lactobacillus and Its Link to Stress Tolerance and Probiotic Properties

“…Due to its elevated negative charge density, it has been suggested that poly-P could aid in the bioremediation of toxic trace elements, acting as a chelating agent for positively charged metals such as mercury or cadmium. Thus, transgenic plants that produce poly-P via the expression of bacterial PPKs have been constructed that showed an increased capacity for mercury accumulation ( Nagata et al, 2010 ; Chang et al, 2015 ). Similarly, recombinant E. coli strains with increased levels of poly-P as a result of PPK overexpression also decreased their sensitivity toward mercury and displayed an increased inorganic mercury accumulation ( Pan-Hou et al, 2002 ; Ruiz et al, 2011 ).…”

A weird DNA band in PCR and its cause

“…Recently, we performed a PCR using a plasmid p(merT merP -merB1-merB2-ppk) [14] as template (Figure 1). The expected DNA band appeared in the agarose gel (Figure 2).…”

“…The plasmid p(merT-merP-merB1-merB2-ppk) and pp(merTmerP-merB1-merB2-pcs1) were stored in our lab [14]. The gene ppk (GenBank accession number: D14445.1) in the plasmid pp(merT-merP-merB1-merB2-ppk) was from the the polyphosphate kinase (ppk) gene isolated from Enterobacter aerogenes [15].…”

“…To exclude the accidental factors, another gene NtPCS1 (GenBank: AY235426.1) was amplified using another plasmid p(merT-merP-merB1-merB2-pcs1) [14] as template. Results showed that the PCR product was normal.…”

Mercury Distribution in Tobacco (<i>Nicotiana tabacum</i>) Cell

“…Although clover and mustard had been selected for removing mercury from soil, the biomass of clover and mustard were small and they were not ideal plants for phytoremediation [4] [14]. Comparatively, tobacco is an ideal plant for constructing genetic-modifying plants for accumulating mercury [23]. The biomass of tobacco plant is large.…”