Abstract
The Mrp (multiple resistance and pH) systems are multi-subunit monovalent cation/proton antiporters. Here, we show that a halotorerant cyanobacterium Aphanothece halophytica has a mrp homologue gene cluster mrpCD1D2EFGAB (Ap-mrp). In proximity to mrpC, NapA type Na+/H+ antiporter (Ap-napA1-2) and bicarbonate transporter (Ap-bicA) genes were found. The Ap-mrpC like cluster was amplified and expressed in the antiporter-deficient Escherichia coli TO114. Cells of TO114 expressing the cluster exhibited resistance to Na+ and Li+. The everted membrane vesicles of TO114 cells expressing the cluster exhibited Na+/H+ and Li+/H+ exchange activities. Physiological role of mrp was analyzed using a mrpA-disrupted mutant of fresh water cyanobacterium Synechococcus elongatus PCC 7942.
