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Rare earth elements have been emitted into the environment largely as fertilizer components. This has caused much fear about whether they would influence our environment, especially on the metabolism and genetics of microorganisms. In this article, the trivalent ion of a rare earth element, lanthanum, was studied for the effects on growth, transformation, and gene expression of Escherichia coli. The results showed that La3+ at concentrations from 50 to 150 μg/mL stimulated the endogenic metabolism and ectogenic metabolism, but had few effects on gene expression. La3+ at lower concentrations from 0.5 to 30 μg/mL inhibit intensively E. coli-absorbing external DNA, decreasing the transformation efficiency. It is also supported by observations using transmission electron microscopy. Our results are significant in understanding the function of rare earth elements to microorganisms and assessing the risk of application of rare earth compounds.