Alterations to dimethylglycine dehydrogenase enables glycine betaine metabolism in Methylorubrum extorquens PA1
Sequenced genomes of evolved isolates of Methylorubrum extorquens PA1 capable of growth upon glycine betaine as a sole carbon and energy source.Study abstract:Low nutrient availability is a key characteristic of the phyllosphere (aerial surface of plants). Phyllospheric bacteria utilize a wide array of carbon sources generated by plant hosts. Glycine betaine is a plant-derived compound that can be metabolized by certain members of the phyllosphere microbiota. Metabolism of glycine betaine generates formaldehyde, an intermediate of methylotrophic metabolism, leading us to investigate how the ubiquitous plant colonizing bacterium M. extorquens PA1 might metabolize GB encountered in its native environment. M. extorquens PA1 cannot utilize GB as a sole carbon source. Through suppressor mutation analysis, we show that M. extorquens PA1 encodes a conserved GB utilization pathway that can be activated by single point mutations conferring GB utilization as a carbon source. We identified the gene cluster encoding the GB catabolic enzymes and found gene expression was induced in the presence of GB. We show that utilization of GB is conserved amongst representative Methylobacterium species and generates the one carbon metabolism intermediate formaldehyde which M. extorquens utilizes as a source of energy. Our results support a model where suppressor mutations in Mext_3745 or ftsH (Mext_4840) prevent the degradation of the dimethylglycine dehydrogenase subunit DgcB by the membrane integral protease FtsH, conferring the ability to utilize GB by either 1) restoring stable membrane topology of DgcB or 2) decreasing FtsH protease activity, respectively. Both mutations alleviate the bottleneck at the second step of GB degradation catalyzed by DgcAB.