A new technique for selection of sensitive and auxotrophic mutants of E. coli: isolation of a strain sensitive to an excess of one-carbon metabolites.

An E. coli strain deleted in the region malasd is used for the selection of conditional or auxotrophic mutants. Thermosensitive and auxotrophic strains have thus been isolated on plates. After selection in liquid medium, a strain has been isolated which is sensitive to excess one-carbon metabolites. It carries two mutations, smg A1 (near metA and arg H), probably identical to relC, and smgB (between asn and ilv), probably part of the E. coli membrane ATPase.