Bacterial Growth at Low Population Densities

Abstract

ACCEPTING Monod's¹ formulation of the relationship between growth-rate (μ) and the concentration of the limiting substrate (s), Herbert et al.² calculated the latter for steady-state conditions in the chemostat as: where D is the dilution-rate (equal to the growth -rate), and K_s and μ_max are growth constants. The concentration of cells produced (x) must be nearly proportional to the consumption of the substrate (s_r – s, s_r being the concentration of the growth-limiting substrate fed into the chemostat), when s is very small as compared with s_r: where y is the yield coefficient which is constant at a given growth-rate. Since s is also constant at a given growth-rate and independent of s_r (ref. 3), x theoretically follows the broken curve in Fig. 1 at low values of s_r. When washout of the population occurs (x = 0), s_r and s become identical and can be taken as the relative threshold concentration of the limiting substrate for growth of a particular organism depending upon the growth-rate given. This was checked experimentally.