Ag. Degermendzhy et al., A NEW EXPERIMENTAL APPROACH TO THE SEARCH FOR CHEMICAL DENSITY FACTORS IN THE REGULATION OF MONOCULTURE GROWTH, Journal of General Microbiology, 139, 1993, pp. 2027-2031
In monocultures of micro-organisms, growth is controlled by feedback m
echanisms involving chemical factors such as limiting substrates and i
nhibitory metabolic products. The role of such feedback in the growth
regulation of Escherichia coli O-124 was investigated by growing cells
in batch culture using a medium containing glucose and mineral salts.
In various phases of growth, portions of the native culture were dilu
ted with culture filtrate, so that although cell density decreased, th
e chemical composition of the growth medium was unaltered. As the dilu
ted cultures grew, variations in growth acceleration were calculated a
nd compared with those of native (undiluted) cultures. Towards the end
of the exponential phase and in the growth deceleration phase, the sp
ecific feedback level (FBL) was between -20 and -200 (h g l-1)-1. The
feedback components resulting from changes in glucose concentration we
re calculated using experimentally determined values of mu(max) (0.55
+/- 0.05 h-1) and K(s) (2.5 +/- 0.7 mg l-1). Only 0.1-40% of FBL could
be accounted for by changes in glucose concentration, indicating the
presence of additional growth regulators. The method developed may bec
ome a new tool for determination of growth-regulating cell-density fac
tors in microbial cultures.