CULTIVATION OF ESCHERICHIA-COLI WITH MIXTURES OF 3-PHENYLPROPIONIC ACID AND GLUCOSE - STEADY-STATE GROWTH-KINETICS

The fate of pollutants in the environment is affected by the presence of easily degradable carbon sources, As a step towards understanding t hese complex interactions, a model system was explored: the degradatio n of mixtures of glucose (i.e., an easily degradable substrate) and 3- phenylpropionic acid (3ppa) (a model pollutant) by Escherichia coli ML 30 was studied systematically in carbon-limited continuous culture, T he two substrates were always consumed simultaneously regardless of th e dilution rate applied, Even at dilution rates higher than the maximu m specific growth rate for 3ppa (0.35 +/- 0.05 h(-1)), the two carbon substrates were utilized together, When cells were grown at a constant dilution rate with different mixtures of 3ppa and glucose, in which 3 ppa contributed between 5 and 90% of carbon substrate in the feed medi um, the steady-state concentrations of 3ppa and glucose were approxima tely proportional to the ratio of the two substrates in the feed mediu m, When cells were cultivated at different dilution rates with a 1:1 m ixture (based on carbon) of glucose and 3ppa, an overall maximum speci fic growth rate of 0.90 +/- 0.05 h(-1) and a Monod substrate saturatio n constant for 3ppa (K-s) of 600 to 700 mu g liter(-1), similar to tha t measured during growth with 3ppa alone, fitted the experimentally de termined steady-state 3ppa concentrations, However, due to the highly differing substrate affinity constants for 3ppa and glucose (K-s simil ar to 30 to 70 mu g liter(-1)), the total steady-state carbon concentr ation in the culture at a constant dilution rate was determined mainly by the steady-state 3ppa carbon concentration, and it increased with increasing proportions of 3ppa in the feed medium.