Alkaline extracellular reduction: isolation and characterization of an alkaliphilic and halotolerant bacterium, Bacillus pseudofirmus MC02


Shun Gui Zhou, Guangdong Institute of Eco-environmental and Soil Sciences, No. 808 Tianyuan Road, Guangzhou 510650, China. E-mail:


Aims:  To isolate an alkaliphilic bacterium and to investigate its ability of extracellular reduction.

Methods and Results:  An alkaliphilic and halotolerant humus-reducing anaerobe, Bacillus pseudofirmus MC02, was successfully isolated from a pH 10·0 microbial fuel cell. To examine its ability of extracellular reduction, AQDS (anthraquinone-2, 6-disulfonae), humic acids (HA) and Fe(III) oxides were chosen as representative electron acceptors. All the experiments were conducted in a pH 9·5 carbonate buffer. The results are as follows: (i) Sucrose, lactate, glucose and glycerol were the favourable electron donors for AQDS reduction by the strain MC02; (ii) The strain had the ability of reducing HA in the presence of sucrose; (iii) It could effectively reduce Fe(III) oxides coupled with sucrose fermentation when AQDS was added as electron shuttle and its Fe(III) reducing capacity ranked as: lepidocrocite (γ-FeOOH) > goethite (α-FeOOH) > haematite(α-Fe2O3); (iv) The strain could decolourize azo dye Orange I.

Conclusions: Bacillus pseudofirmus MC02 was capable of extracellular reduction in AQDS, HA and Fe(III) oxides, and it can be used for decolourizing azo dye (Orange I) in alkaline conditions.

Significance and Impact of the Study:  This is the first report of an alkaliphlic strain of B. pseudofirmus capable of extracellular reduction in AQDS, HA, Fe(III) oxides and decolourization of Orange I. This study could provide valuable information on alkaline biotransformation in the printing and dyeing wastewater and saline-alkali soil.