SIMULTANEOUS UTILIZATION OF PYRIDINE AND FRUCTOSE BY RHODOCOCCUS-OPACUS UFZ-B-408 WITHOUT AN EXTERNAL NITROGEN-SOURCE

A bacterium classified as Rhodococcus opacus, which is able to use pyr idine (a potentially growth-inhibiting substrate) as its sole source o f carbon, energy and nitrogen, was isolated. In a carbon-limited chemo stat culture, the kinetics was determined for growth on both pyridine and a mixture of pyridine and fructose (9 mM/22.15 mM). With growth on pyridine, stable steady states were achieved up to dilution rates of about 0.1 h(-1). A further increase in the dilution rate resulted in t he progressive accumulation of pyridine in the culture liquid and the cells were washed out. The maximum specific growth rate (mu(max) = 0.2 3 h(-1)) and the K-s value (0.22 mM) for growth on pyridine were deter mined from the residual pyridine concentrations measured within the ra nge of stable steady states. With growth on the substrate mixture, the specific pyridine consumption rates and the residual pyridine concent rations were lower at similar dilution rates than with growth on pyrid ine alone, and stable steady states were established at dilution rates of up to 0.13 h(-1). The maximum pyridine degradation rate was enhanc ed to 270 mg pyridine 1(-1) h(-1) compared to 210 mg pyridine 1(-1) h( -1) with growth on pyridine as a single substrate. An external nitroge n source did not need to be added in the case of growth on the substra te mixture. Fructose was assimilated by means of ammonium released fro m pyridine. Analysis of the nitrogen balance furnished proof that pyri dine is an energy-deficient substrate; pyridine was assimilated and di ssimilated at a ratio of 1 mo1/0.67 mol respectively, The resulting yi eld coefficient was about 0.55 g dry weight/g pyridine. Moreover, it w as demonstrated that, in regard to the biologically usable energy, 1 m ol pyridine corresponds to 0.43 mol fructose.