Enrichment and characterization of MTBE-degrading cultures under iron and sulfate reducing conditions

Abstract

The aim of this study was to enrich cultures capable of anaerobic methyl tert-butyl ether (MTBE) biodegradation and to determine their compositions using biomolecular tools. MTBE biodegradation as the sole carbon source was observed under Fe(III) and SO42–reducing conditions and with both electron acceptors present together. The estimated MTBE biodegradation rates ranged from 3.80 to 9.20 mg·L–1·d–1when Fe(III) was the sole electron acceptor, from 1.46 to 1.70 mg·L–1·d–1when Fe(III) and SO42–were present together, and from 1.13 to 1.71 mg·L–1·d–1when SO42–was the sole electron acceptor. Five to eight members were identified in the three consortia, and their characteristics were congruent with the electron acceptor conditions. A clone 99% similar to a recently described MTBE degrader, Ochrobactrum cytisi, was detected in both cultures containing Fe(III). Other 16S rRNA gene sequences detected were highly similar at the species or genus level to additional known MTBE degraders, including Pseudomonas spp. (cometabolic), Sphinogomonas, Achromobacter, and Rhodococcus. Results suggest that the buildup of intermediates and (or) the presence of sulfides had an inhibitory effect on biodegradation. Anaerobic MTBE biodegradation remains poorly understood, and degrading strains still have not been identified to date. This work represents the first detailed 16S rRNA gene profiling of highly enriched iron- and sulfate-reducing MTBE-degrading consortia. These results may provide useful biomarkers to support current efforts for confirming anaerobic MTBE biodegradation in the field.

Anaerobic Methyl tert -Butyl Ether-Degrading Microorganisms Identified in Wastewater Treatment Plant Samples by Stable Isotope Probing

“…Similarly, following continual enrichment of an anaerobic MTBE-degrading consortium, researchers reduced the community to three dominant phylotypes belonging to Deltaproteobacteria, Chloroflexi, and Firmicutes (67). In addition, Clostridia were found in anaerobic MTBE-degrading consortia under sulfate-and iron-reducing conditions (44). These previous studies, combined with the data in the current study, indicate that organisms in the phylum Firmicutes are important for the anaerobic degradation of MTBE.…”

“…Recently, a 16S rRNA gene sequence classifying as a Sphingomonas sp. was found in an MTBE-degrading enrichment culture amended with iron and sulfate as electron acceptors (44). The results of the current study indicate the Sphingopyxis phylotype may be a novel anaerobic MTBE degrader within this family that warrants further investigation for potential anaerobic remediation applications.…”

“…There have been numerous studies on aerobic MTBE biodegradation (29,45,61,62), and microorganisms capable of degrading MTBE under aerobic conditions have been isolated (18,24,36,49). Anaerobic MTBE biodegradation has also been documented (10,19,38,44,(53)(54)(55); however, much less is known about the microorganisms involved and, to date, no MTBE-degrading isolates have been obtained. This knowledge gap is a significant limitation to in situ MTBE bioremediation because many contaminated sites are anaerobic.…”

“…Interestingly, terminal restriction fragment length polymorphism (TRFLP) profiles indicated substantially different community profiles from MTBE-degrading microcosms established from different sediment sources. A third group investigated the microbial community present (using 16S rRNA gene sequencing) when MTBE degradation occurred under sulfate-or iron-reducing conditions or when both electron acceptors were present together and identified five to eight microorganisms in the three consortia (44).…”

Biodegradation of gasoline ether oxygenates

“…The microbial communities in several MTBE-degrading enrichment cultures have been investigated and shown to be dominated by microorganisms from several phylotypes including the Firmicutes phylum that contains acetogens known to O-demethylate aromatic ethers [10 ]. Molecular studies have also been conducted to characterize of microbial communities involved in MTBE biodegradation under Fe-reducing [11] and either sulfatereducing, fumarate-reducing, and antraquinone-2,6-disulfonate-reducing conditions [12].…”