Biodegradation of the metal-cyano complex tetracyanonickelate (II) by Klebsiella oxytoca

Klebsiella oxytoca has been shown to be able to grow on 1-8 mM of tetracyanonickelate (II) [K₂Ni(CN)₄] (TCN), the sole nitrogen source. The biotransformation of 1 mM of TCN to ammonia and methane by resting cells of K. oxytoca was confirmed in this study. The utilization of 1 mM of TCN was strikingly enhanced when 0.8% of glucose was added into the phosphate buffer containing the same amount of resting cells. The growth cells under aerobic conditions had the higher capacity of degrading 1 mM of TCN than cells grown on oxygen-limiting conditions. The consumption of 1 mM of TCN by resting cells of K. oxytoca was induced when the pretreatment of these cells with 1 mM of TCN was conducted. However, the production of methane and acetylene by resting cells pretreated with ammonia (≧1 mM) was inhibited. Thus, ammonia concentrations would affect the degradation of TCN by resting cells of K. oxytoca. This might result from the suppression of nitrogenase activity of K. oxytoca by ammonia. In addition, TCN degradation did not occur in presence of nitrite. This suggests that nitrite might have the toxic effect on bacterial growth. Results from this study also show that TCN biodegradation by cell-free extracts was not observed. This might be due to the oxygen exposure, which caused the inactivation of nitrogenase (oxygen-labile enzyme).