Showing papers by "Bernard D. Davis published in 1950"

Mutants of escherichia coli requiring methionine or vitamin b12

Abstract: The penicillin method (Davis, 1948; Lederberg and Zinder, 1948) has permitted convenient isolation of auxotrophicl mutants of Escherichia coli with specific growth requirements for most of the known water-soluble vitamins, as well as amino acids, purines, and pyrimidines. Accordingly, when crystalline vitamin B12 became available, a search was made for mutants requiring this nutrilite. Several strains of the desired type were promptly recovered. In all cases methionine, but not homocysteine, could be substituted for the vitamin. This paper describes certain biochemical properties of these mutants, as well as of others responding to methionine but not to B,2.

p-Hydroxybenzoic acid; a new bacterial vitamin.

Abstract: MUTANT 83-1 of Escherichia coli, isolated by the penicillin method1, is blocked at an early stage in aromatic synthesis; it responds to a quadruple supplement of tyrosine, phenylalanine, tryptophane and p-aminobenzoic acid. Whereas the quantitative requirements for the three amino-acids are similar to those of mutants with single requirements for these compounds, growth is very slow with 0.005 µgm./ml. of p-aminobenzoic acid, a concentration sufficient for optimal growth of a mutant blocked specifically in p-aminobenzoic acid synthesis. Higher concentrations of the acid, up to 1 µgm./ml., provide more rapid, yet less than normal, growth of mutant 83-1. Normal growth-rate, however, appears with the addition of shikimic acid (a 2,3,4,5-tetrahydrogallic acid).