Na+/H+ exchange activity in the alkaliphile halotolerant cyanobacterium Aphanothece halophytica

作者：Bualuang A****; Soontharapirakkul Kanteera; Incharoensakdi Aran^*

来源：Journal of Applied Phycology, 2010, 22(2): 123-129.

DOI：10.1007/s10811-009-9431-z

• Na+/H+ exchange
• Salt tolerance
• Cyanobacteria
• Aphanothece halophytica
• Alkaliphile

The activity of Na+/H+ exchanger to remove toxic Na+ is important for growth of organisms under high salinity. In this study, the halotolerant cyanobacterium Aphanothece halophytica was shown to possess Na+/H+ exchange activity since exogenously added Na+ could dissipate a pre-formed pH gradient, and decrease extracellular pH. Kinetic analysis yielded apparent K (m) (Na+) and V (max) of 20.7 +/- 3.1 mM and 3,333 +/- 370 nmol H+ min(-1) mg(-1), respectively. For cells grown under salt-stress condition, the apparent K (m) (Na+) and V (max) was 18.3 +/- 3.5 mM and 3,703 +/- 350 nmol H+ min(-1) mg(-1), respectively. Three cations with decreasing efficiency namely Li+, Ca2+, and K+ were also able to dissipate pH gradient. Only marginal exchange activity was observed for Mg2+. The exchange activity was strongly inhibited by Na+-gradient dissipators, monensin, and sodium ionophore as well as by CCCP, a protonophore. A. halophytica showed high Na+/H+ exchange activity at neutral and alkaline pH up to pH 10. Cells grown at pH 7.6 under high salinity exhibited higher Na+/H+ exchange activity than those grown under low salinity during 15 days of growth suggesting a role of Na+/H+ exchanger for salt tolerance in A. halophytica. Cells grown at alkaline pH of 9.0 also exhibited a progressive increase of Na+/H+ exchange activity during 15 days of growth.

• 出版日期2010-4