Functions of a hemolysin-like protein in the cyanobacterium Synechocystis sp. PCC 6803
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A glucose-tolerant strain of the cyanobacterium Synechocystis sp. PCC 6803, generally referred to as wild type, produces a hemolysin-like protein (HLP) located on the cell surface. To analyze the function of HLP, we constructed a mutant in which the hlp gene was disrupted. The growth rate of the mutant was reduced when the cells were stressed by treatment with CuSO4, CdCl2, ZnCl2, ampicillin, kanamycin, or sorbitol in liquid medium, suggesting that HLP may increase cellular resistance to the inhibitory effects of these compounds. Uptake assays with 109Cd2+ using the silicone–oil layer centrifugation technique revealed that both wild type and mutant cells were labeled with 109Cd2+ within 1 min. Although the total radioactivity was much higher in the wild-type cells, 109Cd2+ incorporation was clearly much higher in the mutant cells after adsorbed 109Cd2+ was removed from the cell surface by washing with EDTA. These findings suggest that HLP functions as a barrier against the adsorption of toxic compounds.
KeywordsCell wall Heavy metal stress Hemolysin-like protein S-layer Cyanobacterium
We thank Dr. T. Kuwabara for his critical discussion and advice, and Dr. T. Hama and Miss M. Sawai for operation of the flow cytometer, all of whom are at the University of Tsukuba (UT). The radiolabeling experiments were performed in the Radioisotope Center of UT with their kind help, especially in the 109Cd uptake experiments.
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