A NEW EXPERIMENTAL APPROACH TO THE SEARCH FOR CHEMICAL DENSITY FACTORS IN THE REGULATION OF MONOCULTURE GROWTH

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.