An explanation for the arithmetic linear growth of mycobacteria.

Arithmetic linear growth has been defined by Fisher et al. (1951) as a prolonged growth phase in which bacterial density increases as a straight line function of time. Fisher and Kirchheimer (1952) found this type of growth in 15 different strains of mycobacteria and proposed that arithmetic linear growth is a characteristic feature of members of the genus Mycobacterium. They suggested this phenomenon might be responsible for the relatively slow growth of mycobacteria and provide a basis for the elucidation of some physiologic properties of mycobacteria that distinguish them from nonacid fast microorganisms. The concept of arithmetic linear growth would involve some pattern of reproduction and growth not readily explained in terms of binary fission. On the contrary, arithmetic linear growth of any organism would be expected if some essential nutrient were provided at a constant limiting rate. Data are presented in the present paper which show that cultures of mycobacteria and two other strict aerobes (Micrococcus lysodeikticus and Sarcina lutea) will grow logarithmically when they are aerated continuously by shaking and that arithmetic linear growth is obtained only when the cultures are not aerated.