Catalyzes the ATP-dependent biosynthesis of glutamine from glutamate and ammonia. ATP + L-glutamate + NH4(+) = ADP + H(+) + L-glutamine + phosphate Homooctamer and homotetramer. By nitrogen starvation. Two forms of glutamine synthetase (GSI and GSII) can be found in this nitrogen fixing bacteria, GSI is a typical prokaryotic glutamine synthetase whereas GSII is similar to the eukaryotic enzyme. Belongs to the glutamine synthetase family.