By developing the first bacteria that sense and respond to lanthanides, researchers have advanced the use of living cells to detect and absorb specific metal ions and respond to those ions by changing their functional activity. The work could lead to increased use of bacteria and other live cells to collect lanthanides and other elements in the environment for remediation and other applications. Earlier, Barbara Imperiali at MIT, Karen Allen at Boston University, and coworkers developed lanthanide-binding tags, peptide sequences that selectively bind lanthanide ions with high affinities. Chuan He of the University of Chicago and coworkers have now genetically engineered the tags into live bacteria in a way that enables the microorganisms to sense and respond to lanthanides in the environment (J. Am. Chem. Soc., DOI: 10.1021/ja312032c). In addition to sequestering lanthanides, the engineered bacteria can respond to the metals with gene-expression changes that modify their behavior, such as causing them to move toward areas of greater lanthanide concentration. The system should also be applicable to live-cell sensing of other metal ions, the researchers note.