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 SH7T (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 SH7T, 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 SH7T and Agrobacterium sp. MS2 could be excellent candidates to be used as selective inocula in EMBFR technology for MTBE bioremediation.

An extractive membrane biofilm reactor as alternative technology for the treatment of methyl tert-butyl ether contaminated water.

Among the strategies developed for contaminated groundwater bioremediation, those based on the use of bacteria adhering to inert supports and establishing biofilms have gained great importance in this field. Extractive membrane biofilm reactor (EMBFR) technology offers productive solutions for the removal of volatile and semi-volatile compounds. EMBFR technology is based on the use of extractive semipermeable membranes through which contaminants migrate to the biological compartment in which microorganisms with pollutant biotransformation and/or mineralization capacities can grow, forming an active biofilm on the membrane surface. The objective of this study was to assess the use of three bacterial strains (Paenibacillus sp. SH7 CECT 8558, Agrobacterium sp. MS2 CECT 8557, and Rhodococcus ruber EE6 CECT 8612), as inoculum in a lab-scale EMBFR running for 28 days under aerobic conditions to eliminate methyl tert-butyl ether (MTBE) from water samples. Three different hydraulic retention times (1, 6, and 12 h) were employed. MTBE degradation values were determined daily by a gas GC-MS technique, as well as suspended bacterial growth. The biofilm established by the bacterial strains on the semipermeable membrane was detected by Field-Emission Scanning Electron Microscopy (FESEM) at the end of each experiment. The acute toxicity of the treated effluents and biomedium was determined by Microtox© assay (EC50 ).The results achieved from the MTBE degradation, biofilm formation, and toxicity analysis indicated that bacterial strains MS2 and EE6 were the best options as selective inoculum, although further research is needed, particularly with regard to their possible use as a mixed culture. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1238-1245, 2016.

Characterization of bacterial communities exposed to Cr(III) and Pb(II) in submerged fixed-bed biofilms for groundwater treatment.

Two pilot-scale submerged-bed microbial biofilms were set up for the removal of Cr(III) and Pb(II) from groundwater, and the biological activities and structure of the bacterial communities developed in the presence of the heavy metals were analyzed. Artesian groundwater was polluted with Cr(III) or Pb(II) (15 mg/l) and amended with sucrose (250 mg/l) as carbon source. While Pb(II) was over 99% removed from groundwater during long-term operation (130 days), the efficiency of the removal of Cr(III) significantly decreased in time (95-73% after 60 days). Cr(III)-amended biofilms displayed significant lower sucrose consumption, ATP cell contents and alkaline phosphatase activity, compared to biofilms formed in the presence of Pb(II), while analysis of exopolymers demonstrated significant differences in their composition (content of carbohydrates and acetyl groups) in response to each heavy metal. According to transmission electron microscopy (TEM) and electron-dispersive X-ray analysis (EDX), Cr(III) bioaccumulated in the exopolymeric matrix without entering bacterial cells, while Pb(II) was detected both extra and intracellularly, associated to P and Si. Temperature-gradient gel electrophoresis (TGGE) profiling based on partial amplification of 16S rRNA genes was used to analyze the differences in the structure of the biofilm bacterial communities developed under exposure to each heavy metal. Prevalent populations in the biofilms were further identified by reamplification and sequencing of isolated TGGE bands. 75% of the sequences in the Pb(II) biofilter were evolutively close to the Rhodobacterales, while in the Cr(III) biofilter 43% of the sequences were found affiliated to the Rhizobiales and Sphingomonadales, and 57% to Betaproteobacteria.