MEASUREMENT OF GROWTH AT VERY-LOW RATES (MU-GREATER-THAN-OR-EQUAL-TO-0), AN APPROACH TO STUDY THE ENERGY REQUIREMENT FOR THE SURVIVAL OF ALCALIGENES-EUTROPHUS JMP-134

Alcaligenes eutrophus JMP 134 was grown in a recycling-mode fermenter with 100% biomass retention on 2,4-dichlorophenoxyacetic acid (2,4-D), phenol, and fructose, The growth pattern obtained given a constant su pply of substrates exhibited three phases of linear growth on all thre e substrates, The transition from phase 1 to phase 2, considered to co rrespond to the onset of stringent (growth) control as indicated by a significant increase in guanosine 5'-bisphosphate 3'-bisphosphate (ppG pp), took place at 0.016 h(-1) with 2,4-D and at about 0.02 h(-1) with phenol and fructose, In the final phase, phase 4, which was achieved after the growth rate on the respective substrates fell below 0.003 to 0.001 h(-1), a constant level of biomass was obtained irrespective of further feeding of substrate at the same rate, The yield coefficients decreased by 70 to 80% from phase 1 to phase 3 and were 0 in phase 3, The stationary substrate concentrations s(min) in phase 4, calculated from the kinetic constants of the strain, were 1.23, 0.34, and 0.23 m u M for 2,4-D, phenol, and fructose, respectively, These figures chara cterize the minimum stationary substrate concentrations required in a dynamic system to keep A. eutrophus alive, This is caused by a substra te flux which enables growth at a rate greater than or equal to 0 due to the provision of energy to an extent at least satisfying maintenanc e requirements, According to the constant feed rates of the substrates and the final and stable biomass concentrations, this maintenance ene rgy amounts to 14.4, 4.0, and 2.4 mu mol of ATP . mg of dry mass(-1) h (-1) for 2,4-D, phenol, and fructose, respectively, after correction f or the fraction of living cells, The increased energy expenditure in t he case of 2,4-D is discussed with respect to uncoupling.