Industrial activities such as battery manufacturing can pollute water with lead and other toxic heavy metals. Now, Chinese researchers have designed a way to use microbes to get the lead out. They have engineered bacteria that can detect the toxic metal and remove it from water (Environ. Sci. Technol. 2014, DOI: 10.1021/es4046567).
Although chelating agents and sorbent materials can scrub heavy metals from water, workers still must dispose of the contaminated materials, which can create pollution, says Jing Zhao of Nanjing University and Peking University’s Shenzhen Graduate School. His team has developed a more sustainable approach to recover heavy metals from contaminated water for potential reuse in industry. They recently engineered bacteria to express a gold-binding protein, allowing them to detect the metal and recover it from wastewater (Chem. Sci. 2012, DOI: 10.1039/C2SC01119K). The scientists thought a similar strategy could help them get rid of lead.
So he and colleagues, including Zong-Wan Mao of Sun Yat-Sen University, engineered Escherichia coli to express a lead-binding protein on the cell’s surface. With the protein on the surface, the bacteria can grab large amounts of lead without letting the metal accumulate inside the cells, which can reduce their growth. The researchers also included a set of genes that allowed the bacteria to produce a fluorescent signal when lead binds to the surface proteins.
The modified microbes could collect 5 to 12% of the lead in solutions with concentrations between 5 and 300 μM of the metal. In China, lead concentrations up to 5 μM are allowed in wastewater, but illegal discharge sites may have concentrations of 300 μM or more, according to Zhao.
Although the bacteria’s current lead removal rates are not high enough for treating wastewater, the group plans to optimize the cells to improve their efficiency. Also, to make a practical lead removal system, the team is now designing a way to anchor the bacteria onto polymer membranes or nanomaterials.