Kinetics of molybdenum reduction to molybdenum blue by Bacillus sp. strain A.rzi

Abstract

Molybdenum is very toxic to agricultural animals. Mo-reducing bacterium can be used to immobilize soluble molybdenum to insoluble forms, reducing its toxicity in the process. In this work the isolation of a novel molybdate-reducing Gram positive bacterium tentatively identified as Bacillus sp. strain A.rzi from a metal-contaminated soil is reported. The cellular reduction of molybdate to molybdenum blue occurred optimally at 4 mM phosphate, using 1% (w/v) glucose, 50 mM molybdate, between 28 and 30 °C and at pH 7.3. The spectrum of the Mo-blue product showed a maximum peak at 865 nm and a shoulder at 700 nm. Inhibitors of bacterial electron transport system (ETS) such as rotenone, sodium azide, antimycin A, and potassium cyanide could not inhibit the molybdenum-reducing activity. At 0.1 mM, mercury, copper, cadmium, arsenic, lead, chromium, cobalt, and zinc showed strong inhibition on molybdate reduction by crude enzyme. The best model that fitted the experimental data well was Luong followed by Haldane and Monod. The calculated value for Luong's constants p max, K(s), S(m), and n was 5.88 μmole Mo-blue hr(-1), 70.36 mM, 108.22 mM, and 0.74, respectively. The characteristics of this bacterium make it an ideal tool for bioremediation of molybdenum pollution.

Figure 1

Phylogram (neighbour-joining method) indicating the 16s rRNA genetic relationship between 20 other related references microorganisms from the GenBank database and strain A.rzi. S. marcescens is the outgroup. Species names of bacteria were followed by the accession numbers of 16s rRNA. The internal labels at the branching points are the bootstrap value. Scale bar represents 100 nucleotides substitution.

Figure 2

Time course profile of Mo-blue production from strain A.rzi.

Figure 3

The effect of molybdate on molybdate reduction by strain A.rzi. Error bars represent mean ± standard error (n = 3).

Figure 4

The effect of phosphate on molybdate reduction by strain A.rzi. Error bars represent mean ± standard error (n = 3).

Figure 5

The effect of temperature on molybdate reduction by strain A.rzi. Error bars represent mean ± standard error (n = 3).

Figure 6

Molybdate reduction using various electron donor sources. Error bars represent mean ± standard error (n = 3).

Figure 7

Scanning spectrum of Mo-blue from Bacillus sp. strain A.rzi after 24 hours of static incubation.

Figure 8

The effect of heavy metals (0.1 mM) on molybdate reduction by strain A.rzi. Error bars represent mean ± standard error (n = 3).

Figure 9

Kinetics of molybdenum blue production by strain A.rzi. Data represents mean ± standard error (n = 3).