Comparison of efficiencies and mechanisms of functional flora/strain in degradation of reactive black 5 enhanced by fructose co-metabolism

Abstract:

[Background] Azo dyes and their degradation products are highly toxic and have carcinogenic, teratogenic, and mutagenic effects on organisms. Using co-metabolism to enhance the degradation and removal efficiency of azo dyes by pure cultured bacterial strain or co-cultured flora is environmentally friendly, whereas the comparative study on different efficiencies and mechanisms of bacterial flora/strain under co-substrate regulation needs to be further studied. [Objective] To investigate the efficiencies and mechanisms of functional flora DDMZ1 and strain DDMZ1-1 (identified as Burkholderia sp.) in the degradation and decolorization of reactive black 5 (RB5) enhanced by fructose as a co-substrate. [Methods] The culture conditions of functional flora/strain were optimized, and the decolorization performances and azoreductase activities of functional flora/strain enhanced by fructose co-metabolism were determined. The identification and toxicological assessment of RB5 degradation products were performed by the liquid chromatography/time-of-flight/mass spectrometry (LC-TOF-MS) and phytotoxicity test. The broad-spectrum decolorization performances of functional flora/strain on decolorizing dyes with varied structures were compared and investigated. [Results] The removal efficiencies of RB5 by the functional flora DDMZ1 and Burkholderia sp. DDMZ1-1 under the optimal conditions (pH 5.5, 37 ℃) were 79% and 73%, respectively, and the functional flora exhibited stronger adaptive advantages to the high-salinity environment. The addition of fructose significantly stimulated the decolorization performance of functional flora/strain to RB5 with different initial concentrations. Compared with the flora/strain samples without fructose, those with fructose increased the removal efficiencies of 200 mg/L RB5 by nearly 21% and 27%, respectively. The sample FRU200 (with fructose) significantly stimulated functional flora/strain to secrete extracellular azoreductases after 24 h, thus enhancing the enzyme activity. LC-TOF-MS analysis indicated that RB5 was biodegraded into various metabolites with low molecular weights and simple structures in the fructose co-metabolic system of functional flora DDMZ1. The phytotoxicity of RB5 degradation products in the flora/strain system was significantly reduced via fructose co-metabolism. Compared with Burkholderia sp. DDMZ1-1, the functional flora DDMZ1 exhibited a stronger broad-spectrum degradation ability to dyes with varied structures. [Conclusion] Compared with Burkholderia sp. DDMZ1-1, the functional flora DDMZ1 has better removal efficiency, functional enzyme activity, and product detoxification of RB5 enhanced by fructose co-metabolism. This paper provides a theoretical basis for the application of co-substrate bioaugmentation technology in the treatment of wastewaters containing azo dyes.

Key words:fructose;functional flora/strain;reactive black 5;degradation products;toxicity assessment