Abstract:
A microorganism isolated and identified as Acinetobacter courvalinii was found to be able
to perform sequential free cyanide (CN−) degradation, simultaneous nitrification and aerobic
denitrification (SNaD); this ability was associated with the multiphase growth profile of the
microorganism when provided with multiple nitrogenous sources. The effect of CN− on SNaD
including enzyme expression, activity and protein functionality of Acinetobacter courvalinii was
investigated. It was found that CN− concentration of 1.9 to 5.8 mg CN−/L did not affect the growth
of Acinetobacter courvalinii. Furthermore, the degradation rates of CN− and ammonium-nitrogen
(NH4-N) were found to be 2.2 mg CN−/L/h and 0.40 mg NH4
-N/L/h, respectively. Moreover, five
models’ (Monod, Moser, Generic Rate law, Haldane, and Andrews) ability to predict SNaD under
CN− conditions, indicated that, only the Rate law, Haldane and Andrew’s models, were suited to
predict both SNaD and CN− degradation. The effect of CN− on NH4-N, nitrate-nitrogen (NO3
−)
and nitrite-nitrogen (NO2
−) oxidizing enzymes indicated that the CN− did not affect the expression
and activity of ammonia monooxygenase (AMO); albeit, reduced the expression and activity of
nitrate reductase (NaR) and nitrite reductase (NiR). Nevertheless, a slow decrease in NO2
− was
observed after the supplementation of CN− to the cultures, thus confirming the activity of NaR
and the activation of the denitrification pathway by the CN−. These special characteristics of the
Acinetobacter courvalinii isolate, suggests its suitability for the treatment of wastewater containing
multiple nitrogenous compounds in which CN− is present
