# Enhanced Methyl _Tert_-Butyl Ether Removal by Mixed Consortium: Performance and Adaptability
## 3 Result and Discussion
### The Mixture of Three Pure Cultures Enhanced the Removal of MTBE  
After seven generations of continuous subcultivation and domestication, three strains were highly adaptable to MTBE, and showed different growth and degrading characteristic to different concentrations of MTBE. Hence, three strains were mixed and co-cultured to evaluate the degrading ability of the defined mixed consortium. Figure 2a shows the degradation efficiency of MTBE by three strains and their mixtures. Among them, the M3 strain adapted to the low concentration, yielding 1.646 mg/L of MTBE after 72 h of cultivation at an initial concentration of 10 mg/L. At low concentrations (5-10 mg/L), the \(p\)-value was greater than 0.05, indicating that the difference in MTBE removal efficiency between mixed and pure cultures was not significant. As the concentration of MTBE increased to 30 mg/L, the degradation efficiency by the mixed consortium was about 20% higher than that of any individual. However, the MTBE removal was negatively affected at a high dosage of MTBE at 50 mg/L, decreasing the removal efficiency to 30-40%. In comparison, the mixture of three pure cultures enhanced MTBE removal at 30 mg/L. At high concentrations (30-50 mg/L), the \(p\)-value was less than 0.01, suggesting that there was a significant difference in MTBE removal between the mixed and pure cultures. Figure 1: The growth and removal of MTBE with different concentration by three pure strains. The (**a**) biomass (OD\({}_{5995}\)) and (**b**) degradation efficiency of MTBE was determined after incubation for 72 h at 25 \({}^{\circ}\)C under shaking condition (160 rpm). The error bars represented standard deviation of three independent data. * represents \(p<0.05\); ** represents \(p<0.01\). Similarly, a study compared the removal of 500 mg/L pyrene and 1% w/v tetracosane by 15 oil-degrading microorganisms and their mixture and proposed that the mixed culture SMC had the best performance in hydrocarbons' removal, which promoted the degradation of pyrene and tetracosane by about 13% and 15%, respectively, compared with the best pure strain [27]. In a separate study, six strains with a high degrading ability of petroleum hydrocarbon were selected for the mixed consortium cultivation. Since metabolites produced by one strain could be further decomposed by another, a considerable promotion in degradation efficiency (1.6 to 1.85-fold) was attained by mixed consortium composed of all isolates [28]. While toxic metabolites disturbed biodegradation either by being adsorbed to the cell surface or by inducing mutations in catalytic enzymes, the mixed consortium could prevent the accumulation of toxic intermediates and increase the number of catabolic pathways available for pesticide biodegradation, thus showing an improvement in both microbial survival and removal efficiency [29]. In addition, [PERSON] et al. [30] detected that the activities of enzymes in consortium were highly induced, and the expression and accumulation of bioconversion enzymes may also be responsible for the higher efficiency of consortium. Studies have shown that while pure strains can metabolize compounds, the consortium can expand the extent of degradation owing to the varied enzymatic systems in different organisms [31]. To sum up, the cooperative activities in the mixed consortium enhanced the degradation efficiency of MTBE, especially at higher concentrations (30-50 mg/L). In addition, the effect of the MTBE concentration on biodegradation can be encoded in terms of kinetic parameters obtained by fitting the data (Figure 2b). There was no apparent lack of fit, indicating that both the parameters and models could be adequately applied to describe the trends of MTBE degradation. For MTBE removal by mixed consortium, the data were fitted reasonably well by the Logistic model (R\({}^{2}\) = 0.9997) at a MTBE concentration of 10 mg/L, and the Quiroga-Sales-Romero model (R\({}^{2}\) = 0.9993) simulated the data more accurately as the concentration increased to 30 mg/L.