Decolorization of Orange I under alkaline and anaerobic conditions by a newly isolated humus-reducing bacterium, Planococcus sp. MC01

• Planococcus sp. MC01 anaerobically decolorized Orange I in the optimal pH of 9.0.
• Glucose and sucrose were the effective substrates for decolorization.
• The addition of electron mediators stimulated the decolorization process.
• Low Orange I and high glucose concentration were favor for decolorization.

Printing and dyeing wastewater (PDW) normally has a high pH of 9.0–13.0, but alkaliphilic bacteria capable of treating PDW have rarely been isolated. Here we report an alkaliphilic and halotolerant, humus-reducing facultative anaerobe, Planococcus sp. MC01 (CGMCC 4771 = KCTC 33120), which can effectively reduce AQDS (anthraquinone-2, 6-disulphonate, humus analog) and decolorize Orange I (>94.0%) under alkaline and anaerobic conditions. The decolorization process of Orange I fits a pseudo-first-order kinetics well, and the rate constants (k) were 0.12, 0.17, 0.14, and 0.12 h−1 when acetate, glucose, sucrose, and lactate, respectively, served as electron donor. When 0.5 mmol l−1 AQDS and 2.0 mmol l−1 γ-FeOOH were added as electron shuttles, the decolorization process was stimulated by 44.4% and 32.8%, respectively. Additionally, strain MC01 showed high decolorizing activity with low initial concentrations of Orange I (0.01–0.2 mmol l−1), and the optimal glucose concentration for decolorization was 10.0 mmol l−1. Results of UV/vis spectra suggested the cleavage of the double azo bond during decolorization. To the best of our knowledge, this is the first report of an alkaliphilic facultative anaerobe capable of decolorizing Orange I under alkaline conditions.