GROWTH-RATE DEPENDENT EXPRESSION OF PHENOL ASSIMILATION PATHWAYS IN ALCALIGENES-EUTROPHUS JMP-134 - THE INFLUENCE OF FORMATE AS AN AUXILIARY ENERGY-SOURCE ON PHENOL CONVERSION CHARACTERISTICS

Alcaligenes eutrophus JMP 134 was continuously (carbon-source-limited) grown on phenol to determine the maximum growth rates (mu(max)) as a function of the phenol assimilation pathways expressed. During growth on phenol as the sole source of carbon and energy, an almost exclusive expression of the ortho cleavage pathway (catechol 1,2-dioxygenase) w as observed at initially low growth rates. This allowed a mu(max) of 0 .28 h(-1). The induction of the meta cleavage pathway (catechol 2,3-di oxygenase), which appeared at around 0.25 h(-1), resulted in a further increase in the growth rate to 0.40 h(-1) after the enzyme activities of this pathway had been correspondingly expressed. Hence, two maximu m growth rates, one for the ortho and one for the meta cleavage pathwa y, exist for the growth of A. eutrophus JMP 134 on phenol. Growth on p henol was stimulated by formate, which served as an auxiliary energy s ource in this strain. The simultaneous utilization of phenol and forma te at a molar ratio of 1:5.2 resulted in an increase of the yield coef ficient from about 0.75 g dry mass/g phenol to 1.25 g/g. Furthermore, formate exerted a pronounced effect on the growth rate. At a molar rat io of phenol to formate of 1:4.2, the growth rate was increased to 0.4 2 h(-1), despite the exclusive induction of the ortho cleavage pathway . The meta cleavage pathway was expressed during growth on this substr ate mixture at about 0.4 h(-1). However, this did not enable a signifi cant increase of the growth rate beyond 0.4 h(-1). This is attributed to an exhaustion of the capacity for formate oxidation at this rate. T he results are discussed with respect to energy production capabilitie s when phenol is assimilated as an energy-deficient heterotrophic subs trate.