Role of bacterioferritin comigratory protein and glutathione peroxidase-reductase system in promoting bentazone tolerance in a mutant of Synechococcus elongatus PCC7942

In this article, we describe the modifications in the antioxidant system of Synechococcus elongatus PCC7942 mutant Mu2 capable of growing at five times higher concentration of bentazone than wild type. Nevertheless, in both the strains, bentazone almost identically induced light-dependent H2O2 production and its extracellular release. However unlike the wild type, peroxide produced upon prolong bentazone incubation was immediately degraded in Mu2. Consequently, the lipid peroxidation activity was also kept low. With prolong incubation of bentazone the mutant displayed a steady increase in glutathione peroxidase–reductase enzyme activities and reduced glutathione content, respectively, by 60% and 130%, favoring an efficient detoxification of bentazone-produced H2O2. Catalase–peroxidase and glutathione S-transferase, though present, remained ineffective in rendering bentazone tolerance. In-gel assays of glutathione S-transferase and glutathione reductase revealed presence of between four and five oligomeric states with mobility shifts. One oligomeric form each enzyme in wild-type strain disappeared upon bentazone treatment. Upon two-dimensional electrophoresis and MALDI-TOF/TOF, a bacterioferritin comigratory protein (peroxiredoxin Q) was found to be already highly expressed in Mu2; whereas in wild type, its level increased only upon bentazone exposure. The bcp transcript pool in WT was relatively low but increased with bentazone, whereas Mu2 exhibited high bcp mRNA even without herbicide. Bacterioferritin comigratory protein and glutathione peroxidase–reductase appear to be responsible for detoxification of bentazone-derived peroxide in Mu2.