Delftia acidovorans MC1 resists high herbicide concentrations--a study of nutristat growth on...

Delftia acidovorans MC1 was continuously cultivated under nutristat conditions with elevated concentrations of the herbicides (RS)-2-(2,4-dichlorophenoxy)propionate [(RS)-2,4-DP] and 2,4-dichlorophenoxyacetate (2,4-D). The presence of 1-5 mM of either of these compounds did not essentially inhibit growth. Moreover, substrate consumption was not essentially affected at pH values of 7.0-9.0 selected by reason of alkaline in situ conditions found e.g. on contaminated building rubble but was decreased at pH 9.3. The adenylate energy charge declined to some degree as the herbicide concentration rose, the extent of this increasing as the pH rose. This was caused by an increase in the concentration of ADP and in particular AMP, in contrast to the fairly constant ATP level of around 4 nmol/mg dry mass with (RS)-2,4-DP and 2 nmol/mg with 2,4-D. Comparison of the individual growth parameters with theoretical data taking into account maintenance coefficients of 0.48 mmol (RS)-2,4-DP/g*h and 0.6 mmol 2,4-D/g*h revealed that the culture followed purely kinetic rules. This excludes the necessity of using substrate to a significant extent to satisfy extra efforts in energy for homeostasic work under these accentuated conditions.