Q-198. Use of Co-Substrates and Inhibitors to Investigate Anaerobic MTBE Degradation

L. K. G. Youngster1, P. Somsamak2, M. M. Häggblom1;
1Rutgers, The State Univ. of New Jersey, New Brunswick, NJ, 2Kasetsart Univ., Bangkok, THAILAND.

Contamination of aquifers with the synthetic fuel oxygenate, methyl tert butyl ether (MTBE), is widespread in urban areas around the world. Although use of MTBE in gasoline is declining due to bans in many US and European regions, contamination persists. MTBE is resistant to many physical methods of treating fuel-contaminated water, however, biodegradation may be a useful method of remediation. Microorganisms have been identified that are capable of aerobic MTBE degradation; however, since polluted water systems are often depleted in oxygen due to microbial activity, anaerobic MTBE biodegradation will be essential. Currently, information on anaerobic MTBE degradation is scarce. Anaerobic MTBE degradation has been observed in sediments from a variety of locations and under several redox conditions, but the mechanism and responsible organisms are unknown. We have enriched anaerobic consortia from contaminated sediments and maintained these for over a decade. These are the most enriched MTBE-utilizing anaerobic cultures available for more detailed analysis of the degradation process and factors that affect degradation. Through strategic addition of co-substrates and inhibitors to the MTBE-utilizing enrichment cultures, we have uncovered information about anaerobic MTBE degradation. We show light-reversible inhibition of MTBE-degradation by propyl iodide, suggesting that the MTBE degradation process is corrinoid-dependent. The MTBE-degradation process is not directly coupled to methanogensis or sulfidogenesis and is inhibited by the bacterial inhibitor, rifampicin. These results suggest that the MTBE-degrading organisms are bacteria and that the MTBE-degradation pathway may be acetogenic. Further supporting this hypothesis, we find that many aryl O-methyl ethers that are O-demethylated by acetogenic bacteria, are also O-demethylated by the MTBE-utilizing c enrichment cultures. The addition of these compounds as co-substrates can increase the rate of MTBE-degradation, offering a potentially useful method of stimulating the MTBE-degradation rate in situ.