Effects of overexpression of Escherichia coli katE and bet genes on the tolerance for salt stress in a freshwater cyanobacterium Synechococcus sp PCC7942

To explore the potential role of catalase and glycine betaine in the protec tion of cyanobacteria from damage due to salt stress, we transformed a fres hwater cyanobacterium Synechococcus sp. PCC 7942 with shuttle vectors that contained the Escherichia coli katE. bet, and katE plus bet (katE/bet) gene s. The catalase activity in the cells overexpressing katE and katE/bet gene s was about 1.4-1.8-fold higher than that in the control cells. The control and transformant cells had a similar growth rate in the medium with a low salinity. However, under a high-salinity condition, the cells transformed w ith katE grew faster than the control cells, and the cells expressing katE/ bet genes grew faster than those expressing either the katE or bet gene alo ne. These results indicate that high-salinity caused oxidative stress and t he coexpression of katE and bet genes in Synechococcus cells were superior to the expression of either katE or bet alone for the protection of the cel ls from the damage due to high-salinity. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.