AMMONIUM TRANSPORT IN THERMOPHILIC CYANOBACTERIUM SYNECHOCOCCUS ELONGATUS
1990 Volume 36 Issue 5 Pages 303-308
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1990 Volume 36 Issue 5 Pages 303-308
Ammonium (NH4+) transport in the thermophilic, unicellular, non-nitrogen fixing cyanobacterium Synechococcus elongatus exhibited only one transport system (Km=37.03μM, Vmax=250nmol mg-1 protein min-1). A tenfold concentration gradient was established following 10min of incubation in 60μM 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 20.9kcal/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.
