# 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
[37] proposed that the enrichment of the mixed bacterial cultures DAK11 could effectively degrade PAHs at 500 mg/L, even in the presence of various co-contaminants like petroleum, mono-aromatic hydrocarbons, and heavy metals. [PERSON] [38] illustrated that para-nitrophenol was  
Figure 3: Effect of gasoline organic components on MTBE removal. **(a)** Biodegradation of MTBE in the presence of various gasoline organic components. **(b)** Time course for MTBE degradation and strain growth with or without the addition of BTEX. ** represents \(p<0.01\). degraded co-metabolically by a mixed culture composed of four bacteria, and the mixed culture tolerated and eliminated the negative effects of other co-contaminants. In addition, the effect of BTEX on MTBE degradation rate was further discussed. The trend of residual MTBE concentrations and corresponding biomass as a function of time is present in Figure 3b. It can be seen that MTBE was metabolized in the binary system containing BTEX, but the degradation of substrate was not directly proportional to the increase in biomass. The lag between the increase in biomass and the decrease in concentration may be attributed to the production of intermediates. Moreover, the growth trend and biomass of bacteria were similar before and after BTEX addition. It is supposed that BTEX had no obvious impact on the growth of bacteria. However, it came clear that BTEX delayed the removal of MTBE, and the degradation rate of MTBE in binary mixture was slower than that of MTBE alone. The mechanism of BTEX delaying the degradation of MTBE may be due to the competitive binding between substrates to the active site [39]. In general, toxic intermediates can be metabolized through the synergy between enzymes. However, the coexistence of benzene and toluene with MTBE leads to the accumulation of metabolites with a high toxicity to bacteria, thus inhibiting the removal of MTBE [39]. Similarly, NKNU02 was identified as a MTBE-degrading strain, which could degrade MTBE at a concentration up to 100 mg/L. However, the removal of MTBE by NKNU02 was partially inhibited, decreasing from 60% with MTBE alone to 15% with a mixture of toluene, benzene, o-xylene, and m-xylene [15]. Although MTBE could be degraded by EH831 isolated from oil-contaminated soil without any lag period, the removal of MTBE by EH831 was reduced with the addition of benzene, ethylbenzene, or xylene. In particular, MTBE was not able to be biodegraded in quaternary or quinary mixtures containing ethylbenzene [14]. [PERSON] et al. [35] showed that PM1 could grow on MTBE as carbon source, however, the removal of MTBE by PM1 was completely restrained at toluene concentrations above 60 mg/L or in the presence of 20 mg/L ethylbenzene and xylene. Additionally, the degradation rate of MTBE was significantly slowed down when PM1 was incubated in a mixture of MTBE/benzene or MTBE/toluene. Further, they suggested that although the biodegradation of BTEX and MTBE mainly proceeds through two independent and inducible pathways, the removal of MTBE in groundwater may be delayed until MTBE has migrated outside the BTEX plume. Among BTEX compounds, ethylbenzene and xylene exhibit a greater negative effect on MTBE biodegradation than benzene and toluene [35; 39]. Furthermore, the effect of BTEX on MTBE biodegradation depends on the microbial species and the concentration of contaminants. For example, the diversity of microbial communities' results in a different selectivity and priority for MTBE and BTEX. Moreover, if the concentration of MTBE is high enough or the proportion of BTEX is low, the system will not be disturbed. In a word, the effect of gasoline organic compositions on MTBE degradation deserves extensive attention if the environment is seriously contaminated with gasoline. In addition, the mixture of three pure cultures exhibited a higher adaptability and enhanced MTBE removal in the co-occurrence of other gasoline organic components.