Ammonium Transport in Thermophilic Cyanobacterium Synechococcus Elongatus

Abstract

Ammonium (NH4) transport in the thermophilic, unicellular, non-nitrogen fixing cyanobacterium Synechococcus elongatus exhibited only one transport system (Km = 37.03 UM, Vmax = 250 nmol mg-1 protein min-1). A tenfold concentration gradient was established following 10 min of incubation in 60 jj,u NH4. The rate of NH4 transport was optimum at 50°C but no transport occurred at or below 30°C. Irreversible inactivation of the transport process occurred following exposure of the cells to 70°C. An Arrhenius plot of NH4 uptake (35-50°C) showed that an activation energy of 20.9 kcal/mol was required. The results suggested that the inability of the thermophilic cyanobacterium to grow at lower temperature could be due to unavailability of nutrients. © 1990, Applied Microbiology, Molecular and Cellular Biosciences Research Foundation. All rights reserved.