Increase in the pyridine degradation rate by Rhodococcus opacus UFZ B 408 owing to the simultaneous utilization of a second carbon and energy source

Rhodococcus opacus UFZ B 408 was isolated from soil by its ability to utilize pyridine (a potentially growth-inhibiting substrate) as sole source of carbon, energy and nitrogen. In carbon-substrate-limited chemostat culture, the growth kinetics of R. opacus UFZ B 408 was determined on both pyridine and a mixture of pyridine and fructose (22.15 mM/9 mM). With growth on the substrate mixture the specific pyridine consumption rates as well as the residual pyridine concentrations were lower at similar dilution rates than with growth on pyridine alone. Therefore, with growth on the mixture stable steady states could be established at higher dilution rates and the maximum pyridine degradation rate increased by 28.6% compared to the maximum degradation rate attained with growth on pyridine as single substrate. With growth on the substrate mixture no inorganic nitrogen source had to be added. Fructose was assimilated by means of ammonium released from pyridine. Analysis of the nitrogen balance revealed that pyridine is an energy-deficient substrate; it was assimilated and dissimilated at a ratio of 1 mol/0.67 mol respectively.