Genetic control of ammonium transport in nitrogen fixing cyanobacterium Nostoc muscorum

1617-4623

Springer Online Journal Archives 1860-2000

Biology

Summary Ammonium (NH 4 + ) transport was investigated in Nostoc muscorum ISU (wild type) and spontaneous mutants resistant to cyanophage N-1 (Nm/N-1), streptomycin (Nm/Sm) and methylamine (Nm/MA). N2-fixing wild-type cells transported NH 4 + via two transport systems: the ‘high-affinity’ (K m 11 μM) and ‘low-affinity’ (K m 66 μM), which formed 10 and 50-fold concentration gradients, respectively. The high-affinity system of Nm/MA (K m 11 μM) was similar to the wild type but the low-affinity system had reduced affinity for NH 4 + (K m 125 μM), while Nm/N-1 and Nm/Sm mutants had only a high-affinity transport system (K m 20 and 28 μM, respectively). The growth of mutant Nm/N-1 was more sensitive to 1 mM NH 4 + or methylamine than other strains, and also glutamine-synthetase activity was most reduced in NH 4 + -grown cells. l-methionine-d, l-sulfoximine (20 μM) treatment of N2-grown Nm/N-1 cells resulted in a higher rate of NH 4 + efflux. The apparent alterations in kinetic constants of NH 4 + transport in mutants and glutamine synthetase activity suggested that NH 4 + in N. muscorum is transported by specific carrier(s) and the transport is genetically controlled.

Electronic Resource