Table 4

Expression of the amtB gene and uptake of [14C]methylammonium (MA) by enteric bacteria

StrainExpression of amtB-lacZ,* units/ml per OD600MA uptake, pmol/(ml × OD600 × min)
N-limitingN-excessN-limitingN-excess
E. coli
 NCM1458 (wild type)5,6003152≤3
 NCM2019 (amtB)4,30027≤3≤3
S. typhimurium
 SK2979 (wild type) (18)6,4503534≤3
 SK3020 (ntrC) (18)6337≤3≤3
 SK3004 [ntrB(Con)] (18)10,1005,0005832
 SK3307 (glnA) (24)8,1006,000≤3ND§
 SK3290 [glnA ntrB(Con)]10,4007,400≤3ND§
  • * β-Galactosidase assays were performed with congenic strains carrying the amtB-lacZ fusion, strains NCM2023, NCM2021, SK3362, SK3364, SK3382, SK3381, and SK3379, respectively. 

  • See Materials and Methods

  • Cells were grown in NC medium with glucose (0.4%) as carbon source and glutamine (3 mM) (N-limiting) or glutamine (3 mM) plus ammonium (10 mM) (N-excess). 

  • § Not determined.