NUTRITIONAL-REQUIREMENTS IN MULTIPLE AUXOTROPHIC LACTIC-ACID BACTERIA - GENETIC LESIONS AFFECTING AMINO-ACID BIOSYNTHETIC PATHWAYS IN LACTOCOCCUS-LACTIS, ENTEROCOCCUS-FAECIUM, AND PEDIOCOCCUS-ACIDILACTICI

In a study of genetic lesions responsible for amino acid requirements in multiple auxotrophic lactic acid bacteria, a systematic attempt was made to isolate mutants that could synthesize each of the amino acids required by the parental strains of Lactococcus lactis, Enterococcus faecium, and Pediococcus acidilactici. After treatment with appropriate mutagens or, in some cases, spontaneously, such mutants could indeed be obtained with respect to many but not all essential amino acids. Successful isolation of mutants for a given amino acid means that a minor genetic lesion reparable by single-step mutations affects its biosynthesis; a failure to isolate mutants suggests the involvement of more extensive lesions. Analysis of the results obtained showed certain regularities: some of the biosynthetic pathways for individual amino acids were virtually unaffected or affected by minor lesions in all the strains tested, while others were affected to varying extents among the different strains. Further studies showed that the ability to synthesize a number of amino acids had been acquired simultaneously in several of the amino acid-synthesizing mutants obtained after a single-step mutagenesis in E. faecium and P. acidilactici. Some detailed analysis with one of such mutants from E. faecium showed that a structural alteration of RNA polymerase caused by a single-step mutation is to some extent associated with simultaneous acquisition of the synthetic ability for a number of amino acids.