Molybdenum and heavy metals are toxicants that are needed to be removed from the environment as they are non-biodegradable and pose a serious threat to the ecology. A previously isolated keratin-degrading Bacillus sp. strain khayat was shown to be able to reduce molybdenum (sodium molybdate) to molybdenum blue (Mo-blue). Reduction occurred optimally at the pHs of between 5.8 and 6.8 and temperatures of between 25 and 34��C. Glucose was the best electron donor for supporting molybdate reduction followed by sucrose, fructose, glycogen, lactose, meso-inositol and glycerol in descending order. Other requirements include a phosphate concentration between 5.0 and 7.5�mM and a molybdate concentration of between 10 and 20�mM. The absorption spectrum of the Mo-blue produced was similar to previous Mo-reducing bacterium, and closely resembles a reduced phosphomolybdate. Molybdenum reduction was inhibited by Hg (ii), Ag (i), Cu (ii), As (v) and Pb (ii) at 84.7, 78.9, 53.5, 36.8 and 27.7�%, respectively. Analysis using phylogenetic analysis resulted in a tentative identification of the bacterium as Bacillus sp. strain khayat. The bacterium was unable utilize any of the xenobiotics as sources of electron donor for reduction but the bacterium was able to grow on diesel and SDS. The ability of this bacterium to detoxify several toxicants makes this bacterium an important tool for bioremediation of multiple toxicants. � 2016, Accademia Nazionale dei Lincei.

The first purification of the Mo-reducing enzyme from Serratia sp. strain DRY5 that is responsible for molybdenum reduction to molybdenum blue in the bacterium is reported. The monomeric enzyme has an apparent molecular weight of 105 kDalton. The isoelectric point of this enzyme was 7.55. The enzyme has an optimum pH of 6.0 and maximum activity between 25 and 35°C. The Mo-reducing enzyme was extremely sensitive to temperatures above 50°C (between 54 and 70°C). A plot of initial rates against substrate concentrations at 15 mM 12-MP registered a V m a x for NADH at 12.0 nmole Mo blue/min/mg protein. The apparent K m for NADH was 0.79 mM. At 5 mM NADH, the apparent V m a x and apparent K m values for 12-MP of 12.05 nmole/min/mg protein and 3.87 mM, respectively, were obtained. The catalytic efficiency (k c a t / K m) of the Mo-reducing enzyme was 5.47 M - 1 s - 1. The purification of this enzyme could probably help to solve the phenomenon of molybdenum reduction to molybdenum blue first reported in 1896 and would be useful for the understanding of the underlying mechanism in molybdenum bioremediation involving bioreduction.