Oxidative Assimilation of Amino Acids by Salmonellae in Relation to Growth Rates.

Many species of bacteria form variants which grow slowly on agar media and produce small or dwarf colonies that are only a few tenths of a millimeter or less in diameter. These small colony variants may be isolated directly from nature as in the case of Salmonella typhosa (Jacobsen, 1910; Morris, Barnes, and Sellers, 1943), Corynebacterium diphtheriae, and other bacteria (Morton, 1940). They can also be produced in the laboratory by growing normal, large colony type, bacterial strains of Shigella sp., Salmonella sp., Staphylococcus aureus, Escherichia coli, and other genera and species in media containing toxic inorganic salts or toxic organic compounds such as antibiotics, and also by allowing the cultures to age (Clowes and Rowley, 1955; Stokes and Bayne, 1958a). The dwarf colony variant may differ from the large colony, parent strain in inability to ferment some carbohydrates or to synthesize essential growth factors, or in serological and other properties. Wlhere loss of ability to synthesize known growth factors is involved, large colony growth can be obtained by the addition of adequate amounts of the required vitamins or amino acids to the medium (Weinberg, 1950; Stokes and Bayne, 1958a). In other instances the cause of slow growth has not been determined and decreased permeability to nutrients has been postulated, although the possibility of need for unknown stimulatory growth factors has not been entirely excluded (Clowes and Rowley, 1955; Stokes and Bayne, 1957, 1958a). Some species such as S. pullorum, S. abortusovis, and S. typhisuis, normally grow slowly and form small colonies on solid media.. Such species