Physiological and genetic screening methods for the isolation of methyl tert-butyl ether-degrading bacteria for bioremediation purposes

• A screening method for the isolation of MTBE-degrading bacteria was established.
• 5 strains were selected based on physiological, genetic and ecotoxicological results.
• Selected bacterial strains are promising candidates as MTBE bioremediation inocula.

Bioremediation of groundwater contaminated with methyl tert-butyl ether (MTBE) has been widely described since their cost/efficient ratios are lower than other physic-chemical methodologies. The present study focused on the isolation and selection of MTBE degrading microorganisms from contaminated soil and groundwater samples based on results from growth on mineral media amended with MTBE and BTEX, presence or absence of the monooxygenase genes and specific ability to degrade MTBE. Three bacterial strains were selected and identified as Rhodococcus ruber, strains EE1 (CECT 8555), EE6 (CECT 8612) and A5 (CECT 8556), showing the ability to degrade 60.0, 36.0 and 10.0 mg l−1 MTBE, respectively. Moreover, all the R. ruber strains showed the presence of genes encoding MTBE-degrading enzymes. One isolated strain was identified as Paenibacillus sp. SH7 (CECT 8558) and demonstrated the greatest MTBE degradation value (100 mg l−1), but together with the last strain selected and identified as Agrobacterium sp. MS2 (CECT 8557) did not result in positive amplification of any of the monooxygenase primers tested. The lowest toxicity (as EC50) was observed after 4-days growth of R. ruber EE6 on MTBE-supplemented mineral medium. The potential application of these strains in bioremediation processes is discussed.