Characterization and Complementation of Mutants of Methylobacterium AM1 Which Are Defective in C-1 Assimilation

We investigated eight serine pathway mutants of Methylobacterium AM1; one lacked serine glyoxylate aminotransferase, four were defective in glycerate kinase, and three were blocked in the unknown part of the serine pathway which involves conversion of acetyl-CoA to glyoxylate. We complemented six of these mutants using a gene library of Methylobacterium AM1 DNA and identified two new regions of the chromosome which encode polypeptides necessary for C-1 assimilation. One is an 8·8 kbp HindIII fragment required for the production of glycerate kinase and the other a HindIII fragment of approximately 13 kbp essential for the conversion of acetyl-CoA to glyoxylate. These new C-1 regions of the chromosome are not closely linked to the previously described methanol oxidation genes, nor to a gene required for the production of an active malyl-CoA lyase. Our mutants were also complemented by clones from a gene library of a related pink pigmented facultative methylotroph, Methylobacterium organophilum.