Effect of folic acid analogues on growth and cell division of nonexacting microorganisms.

Studies on the action of analogues of folic acid on microbial growth have been limited mainly to species which require an exogenous supply of folic acid or its derivatives for multiplication. They have been designed principally to determine the nature of the relationship between inhibitor and normal metabolite. The pertinent literature may be found in recent reviews (Martin, 1951; Petering, 1952). The effect of analogues of folic acid on microorganisms which do not exhibit a requirement for exogenous folic acid has been studied less frequently. Such forms usually appear to be susceptible to the analogues, but in relatively higher concentrations (Franklin et al., 1949; Nimmo-Smith and Brown, 1953). The changes induced in susceptible microorganisms by the analogues of folic acid have not been investigated in detail, although there is presumptive evidence from experiments witlh higher forms that such changes are analogous to those which result from a deficiency of the normal metabolite. In addition to the many dependent metabolic processes, folic acid, or the coenzyme form of folic acid, appears essential for mitosis in avian and mammalian cells. Recent work by Jacobson (1954a, 1954b) has shown that the addition of aminopterin to osteoblasts or fibroblasts in tissue culture causes a specific arrest of mitosis at metaphase. This inhibition can be counteracted by the citrovorum factor (leucovorin) but not by folic acid. It appeared of interest, therefore, to (letermine whether analogues of folic acid were capable also of inhibiting cell division in cultures of microoiganisms, particularly those which do 1 Supported in part by a grant from the National Institutes of Health, United States Public Health Service. 2 Special Fellow of the National Institute of Microbiology, National Institutes of Health, Bethesda, and Visiting Fellow in Microbiology, Rutgers University. On leave of absence from the Strangeways Research Laboratory, Cambridge, Englan(l. not exhibit a nutritional requirement for folic acid. Tunnicliff (1939) reported that the inhibition of cellular division produced in bacterial cultures by sulfonamides may be readily observed with organisms of simple nutritional requirements. As is well known, miciobial growth (increase of cellular substance, or volume) and cell division may be considered to some extent as separate and independent processes. In some organisms growth in the absence of cell division, with the formation of filamentous cells, may be induced readily by a variety of factors. However, apart from the observations of Nickerson and Mankowski (1953) that aminopterin (5 X 10-4M) induces an extensive formation of filamentous cells in a medium which normally supports the yeast-type of growth of Candida albicans, no description has been given of the ability of the folic acid analogues to inhibit cell division selectively in microorganisms.