Thymineless death in Escherichia coli in various assay systems: viability determined in liquid medium

Thymineless death has been studied in four different Thy(-) strains of Escherichia coli by using various assay methods including conventional plating techniques as well as one performed entirely in liquid medium. Plating on L agar resulted in a greater loss in viability than the other assay methods, but this extrasensitivity of starved cells to L-agar plating quickly disappeared upon readdition of thymine to the starved cultures. This indicated that cellular damage responsible for the additional killing on L agar is reversible. The results obtained by three other assay methods, the liquid assay, plating on nutrient agar, or plating on tris(hydroxymethyl)aminomethane-minimal agar, did not differ significantly from each other with all strains tested except strain JG 151. In this strain thymineless death was much faster when assayed in the liquid system than by plating. It is suggested that thymineless death detected on nutrient or minimal agar is not a result of plating, but that the lethal event actually occurs during the period of thymine starvation.

Biosynthetic pathway of thiamine pyrophosphate: a special reference to the thiamine monophosphate-requiring mutant and the thiamine pyrophosphate-requiring mutant of Escherichia coli

Two types of mutants of Escherichia coli were isolated, one of which (mutant 70-23-107) responded to thiamine pyrophosphate, and the other (mutant 70-23-102) to thiamine monophosphate and thiamine pyrophosphate. They were produced by further mutation of a thiamine auxotroph of E. coli 70-23 with N-methyl-N'-nitro-N-nitrosoguanidine. The parent organism required thiamine because phosphohydroxymethylpyrimidine kinase activity was lacking in this organism, and hydroxymethylpyrimidine pyrophosphate was not permeable through the cell membrane of E. coli. Thiamine, thiamine monophosphate, and thiamine pyrophosphate were all equally active for the parent, whereas mutants 70-23-102 and 70-23-107 lost their ability to grow on thiamine. Both mutants differed only in the growth response to thiamine monophosphate: the former could grow on thiamine monophosphate, whereas the latter could not. Experimental results with the newly isolated mutants indicate that in E. coli the free form of thiamine is not involved in de novo synthesis of thiamine pyrophosphate, but thiamine monophosphate, an exclusive product formed by the reaction between hydroxymethylpyrimidine pyrophosphate and hydroxyethylthiazole monophosphate, is directly phosphorylated to form thiamine pyrophosphate. Exogenous thiamine, on the other hand, is converted to thiamine pyrophosphate via the intermediate formation of thiamine monophosphate.

Biosynthesis of thiamine pyrophosphate in Escherichia coli

In Escherichia coli, thiamine pyrophosphate is synthesized from thiamine monophosphate. Free thiamine is not involved as an intermediate in de novo synthesis of thiamine pyrophosphate.