Effect of carbon substrate on electron acceptor diauxic lag and anoxic maximum specific growth rate in species with and without periplasmic enzyme

The effect of oxidation state of carbon substrate on the diauxic lag of facultative anaerobic denitrifying bacteria growing aerobically upon switching to anoxic growth was studied. Also studied was the effect on the anoxic maximum specific growth rate. Two pure bacteria cultures were used, Paracoccus pantotrophus, denitrifying bacteria containing a periplasmic nitrate reductase (Nap), and Pseudomonas denitrificans, denitrifying bacteria lacking the periplasmic nitrate reductase. The anoxic maximum specific growth rate of both cultures following a period of aerobic growth with identical dilution up to steady-state was indeed affected by the oxidation state of the carbon, with the most oxidized substrate yielding the highest anoxic maximum specific growth rate. The diauxic lags for Paracoccus pantotrophus were considerably shorter than those for Pseudomonas denitrificans, something expected due to the presence of Nap, an enzyme not affected by aerobiosis. Since the activity of Nap in Paracoccus pantotrophus under aerobic conditions has been shown to increase with the extent of reduction of the carbon substrate, it was also expected that the diauxic lag length for these bacteria would decrease as the reduction state of the carbon substrate increased. This could not be demonstrated, as no significant lags were observed for this species. Pseudomonas denitrificans exhibited a shorter diauxic lag with the more oxidized carbon source.

Keywords:

• Wastewater treatment
• Denitrification.

Notes

^a Trace metal solutions containing 0.5%(w/v) each of CuSO₄, FeCl₃, MnCl₂, and Na₂MoO₄·2H₂O.

*1 h if low initial growth rate is considered a lag.