Toxicity and biofilm-based selection for methyl tert-butyl ether bioremediation technology.

Extractive membrane biofilm reactor (EMBFR) technology offers productive solutions for volatile and semi-volatile compound removal from water bodies. In this study, the bacterial strains Paenibacillus etheri SH7(T) (CECT 8558), Agrobacterium sp. MS2 (CECT 8557) and Rhodococcus ruber strains A5 (CECT 8556), EE6 (CECT 8612) and EE1 (CECT 8555), previously isolated from fuel-contaminated sites, were tested for adherence on tubular semipermeable membranes in laboratory-scale systems designed for methyl tert-butyl ether (MTBE) bioremediation. Biofilm formation on the membrane surface was evaluated through observation by field-emission scanning electron microscope (FESEM) as well as the acute toxicity (as EC50) of the bacterial growth media. Moreover, extracellular polymeric substance (EPS) production for each strain under different MTBE concentrations was measured. Strains A5 and MS2 were biofilm producers and their adherence increased when the MTBE flowed through the inner tubular semipermeable membrane. No biofilm was formed by Paenibacillus etheri SH7(T), nevertheless, the latter and strain MS2 exhibited the lowest toxicity after growth on the EMBFR. The results obtained from FESEM and toxicity analysis demonstrate that bacterial strains R. ruber EE6, A5, P. etheri SH7(T) and Agrobacterium sp. MS2 could be excellent candidates to be used as selective inocula in EMBFR technology for MTBE bioremediation.