Linkage Relationships Between Mutants of Methylobacterium organophilum Impaired in their Ability to Grow on One-carbon Compounds

Abstract

Eight mutant strains of Methylobacterium organophilum which are capable of growing on succinate but not on methanol are described. Three of these contain single enzyme deficiencies while five have pleiotropic deficiencies. Some of the mutant strains are revertible to the wild-type phenotype by N-methyl-N′-nitro-N-nitrosoguanidine and ethyl methanesulphonate and others are not. Crosses between strains were performed by transformation using DNA prepared from cells which were streptomycin-resistant and either methanol+ or methanol−. The frequencies of streptomycin-resistant transformants and methanol+ transformants were determined independently. Four of the methanol− mutant strains appeared to contain mutations which are linked to each other (group 1) while the other four (group 2) appeared to contain mutations not linked to the first four. In reciprocal crosses with the group 2 markers, two appeared to be linked to each other, while the other two were not linked to any mutant tested. The data presented were used to construct a model for the organization of these genes in which the CO-binding cytochrome c is not linked to the five genes for C1-specific enzymes. In this model, the expression of six C1-specific functions is controlled by a common regulatory agent.