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Electrolytic manganese residue (EMR) is a kind of solid waste generated along with the production of electrolytic manganese, with a high content of quartz and metals. The former can be used as silicon fertilizer for crops after activation, while the latter may cause harm to surrounding environment due to their toxicity. The aim of this study was to investigate the effects of bacterial on the activation of silicon and fixation of heavy metals in EMR by using microbe-mineral direct contact and indirect contact methods. Mixed cultures of Bacillus mucilaginosus (BM) and Bacillus circulans (BC) were used to achieve activation of silicon in EMR, and the leaching concentration of Mn, Co and Ni and their chemical forms in the leaching residue were also investigated. The results show that the microbe-mineral direct contact method has better performance for the activation of silicon in EMR with the available silicon in the leaching solution up to 163.27 mg L−1 than the indirect contact method. The metals (Mn, Co and Ni) remaining in the residue mainly exist as the stable state after bioleaching, with lower leaching concentration after bioleaching of 20 d. And the effect of silicon bacteria on activation of silicon and the fixation mechanism of metals including the effect of silicate and silicate bacteria is confirmed, and it is verified by the identification of metabolites and the analysis of chemical reaction process. This study investigates the treatment of EMR by using mixed silicate bacteria, and reveals the mechanisms of bacteria on the activation of silicon and fixaion of heavy metals in EMR. The bioleaching method not only provides silicon source for soil but also can realize the reclamation of EMR.

An open reading frame of 1100 bp in the partially sequenced genome sequence of alkaliphilic Bacillus pseudofirmus OF4 was identified as a putative alanine racemase gene (dadX(OF4)), which was cloned and expressed in Escherichia coli BL21 (DE3). The encoded protein DadX(OF4) was purified to homogeneity by His(6)-tag affinity column, gel filtration and ion-exchange chromatography. The amino acid sequence has highest identity with the known alanine racemase from Oceanobacillus iheyensis HTE831 (48%). The protein was a dimeric, endogenous PLP-dependent enzyme, which was demonstrated by absorption spectra and enzyme activity with or without PLP. The racemization temperature optimum was 40 degrees C and the optimal pH was 10.5. The kinetic parameters K(m) and V(max) at 40 degrees C of alanine racemase, determined by HPLC analysis, were 41.79 mM, 10,500 units/mg for L-alanine and 14.91 mM, 3708 units/mg for D-alanine, respectively.