Transformation of the Streptococcus lactis R Factor to "Folic Acid" by Resting Cell Suspensions of Enterococci.

Although relatively few microorganisms, primarily various lactic acid bacteria, are known to require an exogenous supply of "folic acid" for growth (Snell and Peterson, 1940; Hutchings, Bohonos, and Peterson, 1941; Niven and Sherman, 1944; Stokes, Keresztesy, and Foster, 1944), the presence of this growth factor has been demonstrated in numerous organisms which develop without added folic acid (Hutchings et al., 1941; Thompson, 1942). It appears likely, therefore, that folic acid plays a vital, although as yet unknown, role in the metabolism of all microorganisms. The complex problems of nomenclature, chemistry, and activity for microorganisms and animals of this relatively new growth factor and vitamin and its related forms have been comprehensively reviewed recently by Wieder (1944). For the purposes of the present paper it is sufficient to note that several folic acids, or more correctly Lactobacillus casei factors, have been isolated which vary greatly in activity for Lactobacillus casei and Streptococcus lactis R,1 the two organisms most commonly used in measuring their microbiological activity. Thus the L. casei factor from liver, which is identical, apparently, with the chick antianemia factor, vitamin B¢ (Pfiffner et al., 1943), is highly potent for both bacteria, whereas another factor isolated from yeast is only half as active as the latter for S. lactis R, although fully as active as the latter for L. casei (Stokstad, 1943). A third factor has been isolated (Hutchings, Stokstad, Bohonos, and Slobodkin, 1944) which is almost as potent for L. casei as the liver factor but only 6 per cent as active as the latter for S. lactis R. A fourth factor isolated by Keresztesy, Rickes, and Stokes (1943) and named Streptococcus lactis R factor (SLR factor) differs from the other three in that it does not support growth of L. casei, although it is highly active for S. lactis R. Thus the factors range in potency from little or no growth-promoting activity for one or the other of the two test organisms to high activity for both. That the various growth factors are closely related is clearly evident from their complete interchangeability for the growth of either L. casei or S. lactis R or both. Additional evidence for this close relationship is the fact that streptococci that can utilize the SLR factor invariably convert it during growth into a substance active for L. casei (Stokes, Keresztesy, and Foster, 1944). This was interpreted to mean that growth is due to the ability of those organisms to transform the SLR factor into L. casei activity, and that, therefore, the latter form is the one more directly involved in the metabolism of both types of microorganisms