ANAEROBIC REDUCTIVE DEHALOGENATION: THE LAG PERIOD PRECEEDING HALOAROMATIC DEHALOGENATION, ENRICHMENT OF SEDIMENT ACTIVITY, AND THE PARTIAL CHARACTERIZATION OF A DEHALOGENATING ORGANISM, STRAIN DCB-1 (MICHIGAN)

Anaerobic environments often serve as terminal depositories for the many chemicals released to nature each year. Understanding how localities respond to eliminate these compounds is essential for an appreciation of the total ecology of a region. While certain physical or chemical processes may take place, biological mediation of chemical or pesticide degradation is an integral process in these sites. Since many of these chemicals are haloaromatic molecules, one facet of anaerobic biodegradation involves the dehalogenation of haloaromatic substances.;The lag period preceeding active dehalogenation in sediment is influenced by the number, type and position of the halogen; the concentration of haloaromatic; and the presence of other substituents on the ring. When compared to the corresponding aerobic lag periods, anaerobic adaptation periods are characterized by extreme length followed by rapid dehalogenation. By repeatedly feeding these sediments and diluting with 50% transfers, a consortium was developed that actively dehalogenated 3-bromobenzoate with the benzoate molecule serving as the sole source of carbon and energy.;DCB-1 was identified as a unique, desulfoviridin containing sulfidogenic organism that utilized either sulfite or thiosulfate as an electron acceptor. While thiosulfate, sulfite, and sulfate interfered with dehalogenation, other electron acceptors such as fumarate and nitrate did not. The dehalogenating activity was confined to the substituted benzoates containing one or two meta located halogens. The organism also demethoxylated 3-methoxybenzoate.;My work was divided into four distinct areas: (1) study the lag period proceeding dehalogenation of haloaromatic molecules in anaerobic lake sediments, (2) enrich for the lake sediment dehalogenating activity, (3) further characterize an existing pure culture of "dehalogen" and its unique physiology, and (4) define the positive and negative influences on dehalogenation by the pure culture, strain DCB-1. Hypereutrophic Wintergreen Lake sediments, Kalamazoo County, Michigan, and sewage sludge from the anaerobic digestors at Holt, Michigan, served as natural sources for anaerobic work, while the pure culture (DCB-1) was isolated previously. It is a gram negative rod known to dehalogenate 3-chlorobenzoate in 20% rumen fluid and 0.2% pyruvate.