LAUSR

Sonneratia alba (S. alba) is a mangrove species grown in brackish water of tropical and subtropical regions. Due to its unique environment, it has evolved various mechanisms for modulating salt and metal levels. In order to find the genes connected with bioaccumulation of metals, the root transcriptome annotation of Sonneratia alba was analyzed and a new metallothionein (MT) gene was cloned. Sequence analysis found that the new MT gene belongs to type 3 MT, which is mostly expressed in roots. A simple and efficient method was used to express the type 3 MT of S. alba (SaMT3) by transforming the recombinant expression vector pET15b-SaMT3 into Escherichia coli (E. coli) Rosetta-gami and induction with the optimal conditions of 500 μM Isopropyl β-D-1-thiogalactopyranoside (IPTG) at 24oC for 12 h. OD600 of E. coli cells expressing His fused SaMT3 protein after treated with 500 μM Cu 2+ or 500 μM Pb2+ for 12 h can reach 1.01 or 0.98, while OD600 of control cells expressing His-tag can reach only 0.81 or 0.75. Both control cells and the cells expressing SaMT3 accumulated metals. Cells expressing SaMT3, however, accumulated more Pb2+ and Cu2+ (more than two times) than control cells. In vivo, real-time PCR showed that the SaMT3 transcript was induced significantly when stimulated with 250 μM, 500 μM, or 1,000 μM Cu2+ or Pb2+ for 24 h and 48 h. Taken together, the expression of SaMT3 can increase Cu2+ and Pb2+ resistance and binding capacity of E. coli.