## 3 Results and Discussion
### Degradation Kinetics of Cyanide and NH\({}_{4}\)-N  
An experiment was conducted to investigate the growth of _A. courvaliniii_ under CN\({}^{-}\) conditions, subsequent to CN\({}^{-}\) and TN biodegradation studies by the isolate. The growth of _A. courvalinii_ was shown not to be affected by CN\({}^{-}\) concentration of up to 20 mg CN\({}^{-}\)/L; therefore, it was selected for the assessment of its ability to perform SNaD under cyanogenic conditions. The isolate was found to possess a special ability of sequential utilization of CN\({}^{-}\) and TN by exploiting its multi phased growth attributes, by initially utilizing of CN\({}^{-}\) and subsequently, NH\({}_{4}\)-N, which was evident by the appearance of a secondary logarithmic phase as seen in Figure 1A. Figure 1: Biodegradation kinetics of NH\({}_{4}\)-N and CN\({}^{-}\) by _Acinetobacter courvaliniii_. (**A**): Growth of _Acinetobacter courvaliniii_, sequential degradation of CN\({}^{-}\) and NH\({}_{4}\)-N. (**B**): NO\({}_{2}\)-N and NO\({}_{3}\)-N accumulation and degradation. Figure 1A, demonstrates that _A. courvalini_ utilized CN\({}^{-}\) primarily, from a concentration of 20 mg CN\({}^{-}\)/L to 5.8 mg CN\({}^{-}\)/L followed by NH\({}_{4}\)-N. The rate of degradation for both CN\({}^{-}\) and NH\({}_{4}\)-N was 2.2 mg CN\({}^{-}\)/L/h and 0.40 mg NH\({}_{4}\)-N/L/h, respectively. Moreover, a cyanide-degrading consortium was also assessed (Figure S1 Supplementary file A) as it was having similar attributes to the isolate used in this study; albeit, due to a large percentage of organisms within the consortium being identified as unknown (Figure S2 Supplementary file A), the results were not included nor discussed herein. Overall, an increase of CN\({}^{-}\) in the first 24 h was observed, with a subsequent CN\({}^{-}\) decrease from 58.1 mg CN\({}^{-}\)/L to 5.8 mg CN\({}^{-}\)/L, being observed. The initial increase in CN\({}^{-}\) was associated with the activation of the ANR cascade which result in the production of HCN and denitrification enzymes (NAR, NIR, NOR, and N\({}_{2}\)OR) Figure 1A. [PERSON] et al. [14] reported the regulation of ANR cascade for transcription of denitrification enzymes resulting in the production of HCN by _Pseudomonas aeruginosa_. Moreover, the Pseudomonas have been reported to possess the aerobic denitrification capability needed in the aiding and furtherance of SNaD [15]. _A courvalini_ exibited simillar chareceristics to those of _Pseudomonas sp._ [PERSON] et al. [10] also reported an increase in CN\({}^{-}\) concentration during the expression of denitrification enzymes. For this study, a decrease in NH\({}_{4}\)-N from 64.2 to 28.4 mgNH\({}_{4}\)-N/L was observed, indicating an initiation of nitrification from the threshold limit of 5.8 mg CN\({}^{-}\)/L Figure 1A. This indicated that a concentration of 5.8 mg CN\({}^{-}\)/L did not completely inhibit nitrification; albeit, this concentration is above the threshold concentration of CN\({}^{-}\) known to completely inhibit nitrification reaction [6]. [PERSON] et al. [16] reported the complete inhibition of nitrification by 1 mg CN\({}^{-}\)/L. The inhibition is largely associated with enzyme redundancy, non-production and deactivation. The NAR which is activated during the regulation of ANR is a significant enzyme that aid in aerobic respiration; thus, converting NO\({}_{3}\)-N back into NO\({}_{2}\)-N during aerobic denitrification [17]. The increase of CN\({}^{-}\) during the experiment, confirmed the ability of the _A courvalini_ to induce ANR advocated for its ability to carry out SNaD. Minute accumulation of NO\({}_{2}\)-N was observed compared to NO\({}_{3}\)-N which was produced in significant quantities in the first 24 h of the experiments (Figure 1B). This was deemed normal as some studies have reported that NO\({}_{2}\)-N accumulate in insignificant quantities during SNaD [18].