[en] Monomethylamine (MMA, CH3NH2) can be used as carbon and nitrogen source by many methylotrophic bacteria including Methylobacterium extorquens DM4 which lacks the MMA dehydrogenase-encoded by mau genes, which in M. extorquens AM1 is essential for growth on MMA. Identification and characterization of minitransposon mutants with MMA-dependent phenotype showed that strain DM4 grows with MMA as the sole source of carbon, energy and nitrogen by the N-methylglutamate pathway. Independent mutations were found in a chromosomal region containing genes gmas, mgdABCD, and mgsABC for the three enzymes of the pathway, gamma-glutamylmethylamide (GMA) synthetase, N-methylglutamate (NMG) synthase and NMG dehydrogenase, respectively. RT-PCR confirmed the operonic structure of the two divergent gene clusters mgsABC-gmas and mgdABCD, and their induction during growth with MMA. Genes mgdABCD and mgsABC were found to be essential for utilization of MMA as the carbon and nitrogen source. Gene gmas was essential for MMA utilization as the carbon source, but residual growth was observed for mutant DM4gmas growing with succinate and MMA as the nitrogen source. Plasmid copies of gmas and of the gmas homolog METDI4690 encoding a protein 39% identical to GMAS fully restored the ability of mutants DM4gmas and DM4gmasΔmetdi4690 to use MMA as the carbon and nitrogen source. Similarly, chemically synthesized GMA, the product of gmas, could be used as a nitrogen source for growth in the wild-type strain as well as in DM4gmas and DM4gmasΔmetdi4690 mutants.
