The Influence of pH upon the Growth-Factor Requirements of Bacteria *

The marked effect which minute amounts of tissue and of yeast extracts have upon the growth of organisms has long been known, but the chemical composition of these organic substances, one or more of which are required by many organisms for growth, has been determined only during the past ten years. The determination of the chemical structure of these substances has made it possible to grow many species of organisms upon chemically defined media and to estimate quantitatively their growth-factor requirements. In all this work little attention was paid to the hydrogen ion concentration of the medium, other than to adjust it to a point near that commonly found to be satisfactory for growth of the organism. Brueckner, in 1943, pointed out that the minimum concentration of nicotinic acid required to support maximum growth of a strain o!f Staphylococcus aureus was about ten times greater at a pH of 7.6 than at a pH of 6.2. A difference of this magnitude is of interest from the standpoint of bacterial nutrition and from that of microbiological assay. The main 'object of this investigation was to study in greater detail the influence of pH upon the growth-factor requirements of bacteria growing in chemically defined media.