Cloning, expression, and characterization of cadmium and manganese uptake genes from Lactobacillus plantarum

An Mn2+ and Cd2+ uptake gene, mntA, was cloned from Lactobacillus plantarum ATCC 14917 into Escherichia coli, Its expression conferred on E. coli cell s increased Cd2+ sensitivity as well as energy dependent Cd2+ uptake activi ty. Both transcription and translation of mntA were induced by Mn2+ starvat ion in L, plantarum, as indicated by reverse transcriptase PCR and immunobl otting, Two Cd2+ uptake systems have been identified in L, plantarum: one i s a high-affinity Mn2+ and Cd2+ uptake system that is expressed in Mn2+-sta rved cells, and the other is a nonsaturable Cd2+ uptake system that is expr essed in Cd2+-sufficient cells (Z, Hao, H. R, Reiske, and D, B, Wilson, App l, Environ, Microbiol, 65:592-99, 1999), MntA was not detected in an Mn2+ d ependent mutant of L, plantarum which had lost high-affinity Mn2+ and Cd2uptake activity. The results suggest that mntA is the gene encoding the hig h-affinity Mn2+ and Cd2+ transporter. On the basis of its predicted amino a cid sequence, MntA belongs to the family of P-type cation-translocating ATP ases, The topology and potential Mn2+- and Cd2+-binding sites of MntA are d iscussed. A second clone containing a low-affinity Cd2+ transport system wa s also isolated.