Catalyzes the ATP-dependent biosynthesis of glutamine from glutamate and ammonia. ATP + L-glutamate + NH4(+) = ADP + H(+) + L-glutamine + phosphate Binds 2 Mg(2+) ions per subunit. Inhibited by methionine sulfoximine, ADP and pyrophosphate, but not by various nitrogen-containing metabolites that inhibit other GS enzymes. Optimum pH is 6.8. Optimum temperature is 50 degrees Celsius. Homooctamer. Can grow, in the absence of GSI and GSII glutamine synthetases, without a glutamine supplement in minimal medium that contains both ammonium and glutamate. However, given the high glutamate and ammonium substrate Km values, glutamine synthase is probably a secondary activity of GlnT. Two forms of glutamine synthetase (GSI and GSIII) can be found in this nitrogen fixing bacteria, GSI is a typical prokaryotic glutamine synthetase whereas GSIII is a divergent type with very low sequence similarity to the type I and II enzymes. Belongs to the glutamine synthetase family.