Characteristics and regulation of ammonium (methylammonium) transport in Rhizobium meliloti

Abstract Rhizobium meliloti can synthesize an ammonium carrier as demonstrated by concentrative methylammonium uptake ( K _m= 2 μ M), which is competitively inhibited by ammonium ( K _i= 1.2 μ M). The carrier is under nitrogen control: its synthesis is repressed by ammonium, glutamine and asparagine. The asparagine effect may be of importance for the transfer of ammonia from the bacterium to the plant in the nodule.