Expression of mammalian metallothionein-I gene in cyanobacteria to enhanceheavy metal resistance

Metallothionein (MT) from mammals is a low molecular weight (about 6-7 KD), and cystein-rich (20 cystein per molecular) protein (Vallee, 1991), So MT has the strong binding ability of metal such as Cd, Hg and Pd, Wild-typed c yanobacteria have their own metallothionein-like proteins, which are of low cysteine content and have weak ability to bind heavy metal. Therefore, it is imperative to transfer the MT-I gene from mammal into cyanobacteria cell for the absorption and accumulation of heavy metals in aqueous system incl uding marine and lake (Misra and Gedamu, 1989), We inserted the MT-I cDNA g ene after the strong promoter PpsbA or Psmt into the intermediary vector pR L-439, and then pRL-MT was ligated with shuttle vector pKT-210 (a shuttle v ector pDC-08 was used at an earlier time) to construct the shuttle expressi on vector pKT-MT, (The MT-I mutant alpha-KKS-alpha also was selected as aim gene.) Then the constructed vector was introduced into cyanobacterium Anab aena sp, PCC7120, Synechocystis sp, PCC6803 and Synechococcus sp, PCC7942 w ith triparental conjunctive transfer (Bryant, 1994), The expression efficie ncy is about 1%, We also used homologous recombination vector pTZ18-8 to in troduce MT-I cDNA into chromosomes in cyanobacteria and got higher expressi on efficiency. Metal tolerance tests show that the transgenic cyanobacteria acquire metal resistance up to 60 mu mol/g CdCl2 and expression efficiency up to 1045 mu g MT/g fresh cells according to the data of ELISA, (C) 1999 Published by Elsevier Science Ltd. All rights reserved.